Functional and targeted proteomics characterization of a human primary endothelial cell model of the blood-brain barrier (BBB) for drug permeability studies

The blood-brain barrier (BBB) protects the brain from toxins but hinders the penetration of neurotherapeutic drugs. Therefore, the blood-to-brain permeability of chemotherapeutics must be carefully evaluated. Here, we aimed to establish a workflow to generate primary cultures of human brain microvascular endothelial cells (BMVECs) to study drug brain permeability and bioavailability. Furthermore, we characterized and validated this BBB model in terms of quantitative expression of junction and drug-transport proteins, and drug permeability. We isolated brain microvessels (MVs) and cultured BMVECs from glioma patient biopsies. Then, we employed targeted LC-MS proteomics for absolute protein quantification and immunostaining to characterize protein localization and radiolabeled drugs to predict drug behavior at the Human BBB. The abundance levels of ABC transporters, junction proteins, and cell markers in the cultured BMVECs were similar to the MVs and correctly localized to the cell membrane. Permeability values (entrance and exit) and efflux ratios tested in vitro using the primary BMVECs were within the expected in vivo values. They correctly reflected the transport mechanism for 20 drugs (carbamazepine, diazepam, imipramine, ketoprofen, paracetamol, propranolol, sulfasalazine, terbutaline, warfarin, cimetidine, ciprofloxacin, digoxin, indinavir, methotrexate, ofloxacin, azidothymidine (AZT), indomethacin, verapamil, quinidine, and prazosin). We established a human primary in vitro model suitable for studying blood-to-brain drug permeability with a characterized quantitative abundance of transport and junction proteins, and drug permeability profiles, mimicking the human BBB. Our results indicate that this approach could be employed to generate patient-specific BMVEC cultures to evaluate BBB drug permeability and develop personalized therapeutic strategies.

Is Curfew Effective in Limiting SARS-CoV-2 Progression? An Evaluation in France Based on Epidemiokinetic Analyses

BACKGROUND

Since late summer 2020, the French authorities implemented a curfew/lightened lockdown-alternating strategy instead of strict lockdown, to improve acceptability and limit socioeconomic consequences. However, data on curfew-related efficacy to control the epidemic are scarce.

OBJECTIVE

To investigate the effects on COVID-19 spread in France of curfew combined to local and/or nationwide restrictions from late summer 2020 to mid-February 2021.

DESIGN

We conducted a comparative evaluation using a susceptible-infected-recovered (SIR)-based model completed with epidemiokinetic tools.

MAIN MEASURES

We analyzed the time-course of epidemic progression rate under curfew in French Guyana and five metropolitan regions where additional restrictions were implemented at different times. Using linear regressions of the decay/increase rates in daily contaminations, we calculated the epidemic regression half-lives (t_1/2β) for each identified period.

KEY RESULTS

In French Guyana, two decay periods with rapid regression (t_1/2β of ~10 days) were observed under curfew, with slowing (t_1/2β of ~43 days) when curfew was lightened. During the 2-week pre-lockdown curfew (2020/10/17-2020/11/02) in Provence-Alpes-Côte-d'Azur, Auvergne-Rhône-Alpes, and Ile-de-France, the epidemic progression was unchanged. During the post-lockdown curfew (2020/12/15-2020/02/14), the epidemic slowly regressed in Grand-Est (t_1/2β of ~37 days), whereas its progression rate plateaued in Auvergne-Rhône-Alpes and increased immediately in Provence-Alpes-Côte-d'Azur, Ile-de-France, and Nouvelle-Aquitaine, whatever the curfew starting time was (06:00 or 08:00 pm). Interestingly, a delayed slow decay (17 days < t_1/2β < 64 days) occurred under curfew in all regions except Ile-de-France.

CONCLUSIONS

Curfew allowed the temporary control of SARS-CoV-2 epidemic, however variably in the French regions, without preventing lockdown necessity. To accelerate the epidemic regression such as observed in French Guyana, curfew should be implemented timely with additional restrictions.

Is Lockdown Effective in Limiting SARS-CoV-2 Epidemic Progression?-a Cross-Country Comparative Evaluation Using Epidemiokinetic Tools

BACKGROUND

To date, the risk/benefit balance of lockdown in controlling severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) epidemic is controversial.

OBJECTIVE

We aimed to investigate the effectiveness of lockdown on SARS-CoV-2 epidemic progression in nine different countries (New Zealand, France, Spain, Germany, the Netherlands, Italy, the UK, Sweden, and the USA).

DESIGN

We conducted a cross-country comparative evaluation using a susceptible-infected-recovered (SIR)-based model completed with pharmacokinetic approaches.

MAIN MEASURES

The rate of new daily SARS-CoV-2 cases in the nine countries was calculated from the World Health Organization's published data. Using a SIR-based model, we determined the infection (β) and recovery (γ) rate constants; their corresponding half-lives (t1/2β and t1/2γ); the basic reproduction numbers (R0 as β/γ); the rates of susceptible S(t), infected I(t), and recovered R(t) compartments; and the effectiveness of lockdown. Since this approach requires the epidemic termination to build the (I) compartment, we determined S(t) at an early epidemic stage using simple linear regressions.

KEY RESULTS

In New Zealand, France, Spain, Germany, the Netherlands, Italy, and the UK, early-onset stay-at-home orders and restrictions followed by gradual deconfinement allowed rapid reduction in SARS-CoV-2-infected individuals (t1/2β ≤ 14 days) with R0 ≤ 1.5 and rapid recovery (t1/2γ ≤ 18 days). By contrast, in Sweden (no lockdown) and the USA (heterogeneous state-dependent lockdown followed by abrupt deconfinement scenarios), a prolonged plateau of SARS-CoV-2-infected individuals (terminal t1/2β of 23 and 40 days, respectively) with elevated R0 (4.9 and 4.4, respectively) and non-ending recovery (terminal t1/2γ of 112 and 179 days, respectively) was observed.

CONCLUSIONS

Early-onset lockdown with gradual deconfinement allowed shortening the SARS-CoV-2 epidemic and reducing contaminations. Lockdown should be considered as an effective public health intervention to halt epidemic progression.

Brain Distribution of Drugs: Brain Morphology, Delivery Routes, and Species Differences

Neuropharmacokinetics considers cerebral drug distribution as a critical process for central nervous system drug action as well as for drug penetration through the CNS barriers. Brain distribution of small molecules obeys classical rules of drug partition, permeability, binding to fluid proteins or tissue components, and tissue perfusion. The biodistribution of all drugs, including both small molecules and biologics, may also be influenced by specific brain properties related to brain anatomy and physiological barriers, fluid dynamics, and cellular and biochemical composition, each of which can exhibit significant interspecies differences. All of these properties contribute to select optimal dosing paradigms and routes of drug delivery to reach brain targets for classical small molecule drugs as well as for biologics. The importance of these properties for brain delivery and exposure also highlights the need for efficient new analytical technologies to more comprehensively investigate drug distribution in the CNS, a complex multi-compartmentalized organ system.

Intracellular ABCB1 as a Possible Mechanism to Explain the Synergistic Effect of Hydroxychloroquine-Azithromycin Combination in COVID-19 Therapy

The co-administration of hydroxychloroquine with azithromycin is proposed in COVID-19 therapy. We hypothesize a new mechanism supporting the synergistic interaction between these drugs. Azithromycin is a substrate of ABCB1 (P-glycoprotein) which is localized in endosomes and lysosomes with a polarized substrate transport from the cell cytosol into the vesicle interior. SARS-CoV-2 and drugs meet in these acidic organelles and both basic drugs, which are potent lysosomotropic compounds, will become protonated and trapped within these vesicles. Consequently, their intra-vesicular concentrations can attain low micromolar effective cytotoxic concentrations on SARS-CoV-2 while concomitantly increase the intra-vesicular pH up to around neutrality. This last effect inhibits lysosomal enzyme activities responsible in virus entry and replication cycle. Based on these considerations, we hypothesize that ABCB1 could be a possible enhancer by confining azithromycin more extensively than expected when the trapping is solely dependent on the passive diffusion. This additional mechanism may therefore explain the synergistic effect when azithromycin is added to hydroxychloroquine, leading to apparently more rapid virus clearance and better clinical benefit, when compared to monotherapy with hydroxychloroquine alone.

ABC Transporters at the Blood-Brain Interfaces, Their Study Models, and Drug Delivery Implications in Gliomas

Drug delivery into the brain is regulated by the blood-brain interfaces. The blood-brain barrier (BBB), the blood-cerebrospinal fluid barrier (BCSFB), and the blood-arachnoid barrier (BAB) regulate the exchange of substances between the blood and brain parenchyma. These selective barriers present a high impermeability to most substances, with the selective transport of nutrients and transporters preventing the entry and accumulation of possibly toxic molecules, comprising many therapeutic drugs. Transporters of the ATP-binding cassette (ABC) superfamily have an important role in drug delivery, because they extrude a broad molecular diversity of xenobiotics, including several anticancer drugs, preventing their entry into the brain. Gliomas are the most common primary tumors diagnosed in adults, which are often characterized by a poor prognosis, notably in the case of high-grade gliomas. Therapeutic treatments frequently fail due to the difficulty of delivering drugs through the brain barriers, adding to diverse mechanisms developed by the cancer, including the overexpression or expression de novo of ABC transporters in tumoral cells and/or in the endothelial cells forming the blood-brain tumor barrier (BBTB). Many models have been developed to study the phenotype, molecular characteristics, and function of the blood-brain interfaces as well as to evaluate drug permeability into the brain. These include in vitro, in vivo, and in silico models, which together can help us to better understand their implication in drug resistance and to develop new therapeutics or delivery strategies to improve the treatment of pathologies of the central nervous system (CNS). In this review, we present the principal characteristics of the blood-brain interfaces; then, we focus on the ABC transporters present on them and their implication in drug delivery; next, we present some of the most important models used for the study of drug transport; finally, we summarize the implication of ABC transporters in glioma and the BBTB in drug resistance and the strategies to improve the delivery of CNS anticancer drugs.

Integrated Pharmacokinetic/Pharmacodynamic Model of a Bispecific CD3xCD123 DART Molecule in Nonhuman Primates: Evaluation of Activity and Impact of Immunogenicity

Purpose: Flotetuzumab (MGD006 or S80880) is a bispecific molecule that recognizes CD3 and CD123 membrane proteins, redirecting T cells to kill CD123-expressing cells for the treatment of acute myeloid leukemia. In this study, we developed a mathematical model to characterize MGD006 exposure-response relationships and to assess the impact of its immunogenicity in cynomolgus monkeys.Experimental Design: Thirty-two animals received multiple escalating doses (100-300-600-1,000 ng/kg/day) via intravenous infusion continuously 4 days a week. The model reflects sequential binding of MGD006 to CD3 and CD123 receptors. Formation of the MGD006/CD3 complex was connected to total T cells undergoing trafficking, whereas the formation of the trimolecular complex results in T-cell activation and clonal expansion. Activated T cells were used to drive the peripheral depletion of CD123-positive cells. Anti-drug antibody development was linked to MGD006 disposition as an elimination pathway. Model validation was tested by predicting the activity of MGD006 in eight monkeys receiving continuous 7-day infusions.Results: MGD006 disposition and total T-cell and CD123-positive cell profiles were well characterized. Anti-drug antibody development led to the suppression of T-cell trafficking but did not systematically abolish CD123-positive cell depletion. Target cell depletion could persist after drug elimination owing to the self-proliferation of activated T cells generated during the first cycles. The model was externally validated with the 7-day infusion dosing schedule.Conclusions: A translational model was developed for MGD006 that features T-cell activation and expansion as a key driver of pharmacologic activity and provides a mechanistic quantitative platform to inform dosing strategies in ongoing clinical studies. Clin Cancer Res; 24(11); 2631-41. ©2018 AACR.

Age-Dependent Regulation of the Blood-Brain Barrier Influx/Efflux Equilibrium of Amyloid-β Peptide in a Mouse Model of Alzheimer's Disease (3xTg-AD)

The involvement of transporters located at the blood-brain barrier (BBB) has been suggested in the control of cerebral Aβ levels, and thereby in Alzheimer's disease (AD). However, little is known about the regulation of these transporters at the BBB in animal models of AD. In this study, we investigated the BBB expression of Aβ influx (Rage) and efflux (Abcb1-Abcg2-Abcg4-Lrp-1) transporters and cholesterol transporter (Abca1) in 3-18-month-old 3xTg-AD and control mice. The age-dependent effect of BBB transporters regulation on the brain uptake clearance (Clup) of [3H]cholesterol and [3H]Aβ1 - 40 was then evaluated in these mice, using the in situ brain perfusion technique. Our data suggest that transgenes expression led to the BBB increase in Aβ influx receptor (Rage) and decrease in efflux receptor (Lrp-1). Our data also indicate that mice have mechanisms counteracting this increased net influx. Indeed, Abcg4 and Abca1 are up regulated in 3- and 3/6-month-old 3xTg-AD mice, respectively. Our data show that the balance between the BBB influx and efflux of Aβ is maintained in 3 and 6-month-old 3xTg-AD mice, suggesting that Abcg4 and Abca1 control the efflux of Aβ through the BBB by a direct (Abcg4) or indirect (Abca1) mechanism. At 18 months, the BBB Aβ efflux is significantly increased in 3xTg-AD mice compared to controls. This could result from the significant up-regulation of both Abcg2 and Abcb1 in 3xTg-AD mice compared to control mice. Thus, age-dependent regulation of several Aβ and cholesterol transporters at the BBB could ultimately limit the brain accumulation of Aβ.

Toxicokinetics of Colchicine in Humans: Analysis of Tissue, Plasma and Urine Data in Ten Cases

1 A specific and sensitive radioimmunoassay was used to study the toxicokinetics of colchicine in seven cases of acute human poisoning. Post-mortem tissue concentrations of colchicine were measured in three further cases.

Depending on the time of patient admission, two disposition processes could be observed. The first, in three patients, admitted early, showed a bi-exponential plasma colchicine decrease, with distribution half-lives of 30, 45 and 90 min. The second, in four patients, admitted late, showed a mono-exponential decrease. Plasma terminal half-lives ranged from 10.6 to 31.7 h for both groups.

2 Pharmacokinetic analysis of urine colchicine data was performed for two patients. The fraction of unchanged colchicine excreted in urine was about 30%, renal clearance was about 131 h-1 and three-fold less than total body clearance (391 h-1). The apparent volume of distribution was 211 kg-1.

3 Post-mortem tissue analysis showed an ubiquitous colchicine distribution. Colchicine accumulated at high concentrations in the bone marrow (more than 600 ng g-1), testicle (400 ng g-1), spleen (250 ng g-1), kidney (200 ng g-1), lung (200 ng g-1) and heart (95 ng g -1); it was also found in the brain (125 ng g-1).

4 This toxicokinetic study shows that after massive ingestion, the disposition parameters and kinetics of colchicine are not markedly modified from those occuring in healthy volunteers. The absorption process was not delayed and the distribution and elimination half-lives were in the range known to occur with therapeutic doses.

Methadone dose in heroin-dependent patients: role of clinical factors, comedications, genetic polymorphisms and enzyme activity

AIMS

Methadone is characterized by wide intersubject variability regarding the dose needed to obtain full therapeutic response. We assessed the influence of sociodemographic, ethnic, clinical, metabolic and genotypic variables on methadone maintenance dose requirement in opioid-dependent responder patients.

METHODS

Eighty-one stable patients (60 men and 21 women, 43.7 ± 8.1 years old, 63.1 ± 50.9 mg day(-1) methadone), divided into quartiles with respect to the median daily dose, were enrolled and underwent clinical examination, treatment history and determination of liver/intestinal cytochrome P450 (CYP) 3A4 activity measured by the midazolam test, R,S-methadone trough concentration and clinically significant polymorphisms of the OPRM1, DRD2, COMT, ABCB1, CYP2B6, CYP3A5, CYP2C19 and CYP2D6 genes.

RESULTS

Methadone maintenance dose was correlated to the highest dose ever used (r(2) = 0.57, P < 0.0001). Fractioned methadone intake (odds ratio 4.87, 95% confidence interval 1.27-18.6, P = 0.02), bodyweight (odds ratio 1.57, 95% confidence interval 1.01-2.44, P = 0.04), history of cocaine dependence (80 vs. 44 mg day(-1) in never-addict patients, P = 0.005) and ethnicity (Asian > Caucasian > African, P = 0.04) were independently associated with high-dose methadone in multiple regression analysis. A modest correlation was observed between liver/intestinal CYP3A4 activity and methadone dose at steady state (Spearman rank correlation coefficient [rs ] = 0.21, P = 0.06) but not with highest dose ever used (rs = 0.15, P = 0.18) or dose-normalized R,S-methadone trough concentrations (rs = -0.05, P = 0.64). Concomitant CYP3A4 inhibitors only affected the relationship between methadone dose and R,S-methadone trough concentration. None of the genetic polymorphisms explored was predictive of the methadone maintenance dose.

CONCLUSIONS

Methadone maintenance dose was predicted by sociodemographic and clinical variables rather than genetic polymorphisms or liver/intestinal CYP3A4 activity in stable patients.

Blood-brain and retinal barriers show dissimilar ABC transporter impacts and concealed effect of P-glycoprotein on a novel verapamil influx carrier

BACKGROUND AND PURPOSE

The respective impact and interplay between ABC (P-glycoprotein/P-gp/Abcb1a, BCRP/ABCG2, MRP/ABCC) and SLC transporter functions at the blood-brain barrier (BBB) and blood-retinal barriers (BRB) are incompletely understood.

EXPERIMENTAL APPROACH

We measured the initial cerebral and retinal distribution of selected ABC substrates by in situ carotid perfusion using P-gp/Bcrp knockout mice and chemical ABC/SLC modulation strategies. P-gp, Bcrp, Mrp1 and Mrp4 were studied by confocal retina imaging.

KEY RESULTS

Chemical or physical disruption of P-gp increased [(3) H]-verapamil transport by ~10-fold at the BBB and ~1.5-fold at the BRB. [(3) H]-Verapamil transport involved influx-mediated by an organic cation clonidine-sensitive/diphenhydramine-sensitive proton antiporter at both barriers; this effect was unmasked when P-gp was partially or fully inhibited/disrupted at the BBB. Studies of [(3) H]-mitoxantrone and [(3) H]-zidovudine transport suggested, respectively, that Bcrp efflux was less involved at the BRB than BBB, whereas Mrps were significantly and similarly involved at both barriers. Confocal imaging showed that P-gp and Bcrp were expressed in intra-retinal vessels (inner BRB/iBRB) but absent from the blood/basal membrane of cells of the retinal pigment epithelium (outer BRB/oBRB/RPE) where, in contrast, Mrp1 and Mrp4 were localized.

CONCLUSIONS AND IMPLICATIONS

P-gp, Bcrp, Mrp1 and Mrp4 are differentially expressed at the outer and inner BRB, resulting in an altered ability to limit substrate distribution at the retina as compared with the BBB. [(3) H]-Verapamil distribution is not P-gp-specific and involves a proton antiporter at both the BBB and BRB. However, this transport is concealed by P-gp at the BBB, but not at the BRB, where P-gp activity is reduced.

Pharmacophore-based discovery of inhibitors of a novel drug/proton antiporter in human brain endothelial hCMEC/D3 cell line

BACKGROUND AND PURPOSE

An influx drug/proton antiporter of unknown structure has been functionally demonstrated at the blood-brain barrier. This transporter, which handles some psychoactive drugs like diphenhydramine, clonidine, oxycodone, nicotine and cocaine, could represent a new pharmacological target in drug addiction therapy. However, at present there are no known drugs/inhibitors that effectively inhibit/modulate this transporter in vivo.

EXPERIMENTAL APPROACH

The FLAPpharm approach was used to establish a pharmacophore model for inhibitors of this transporter. The inhibitory potency of 44 selected compounds was determined against the specific substrate, [(3)H]-clonidine, in the human cerebral endothelial cell line hCMEC/D3 and ranked as good, medium, weak or non-inhibitor.

KEY RESULTS

The pharmacophore model obtained was used as a template to screen xenobiotic and endogenous compounds from databases [Specs, Recon2, Human Metabolome Database (HMDB), human intestinal transporter database], and hypothetical candidates were tested in vitro to determine their inhibitory capacity with [(3)H]-clonidine. According to the transporter database, 80% of the proton antiporter inhibitor candidates could inhibit P-glycoprotein/MDR1/ABCB1 and specificity is improved by reducing inhibitor size/shape and increasing water solubility. Virtual screening results using HMDB and Recon2 for endogenous compounds appropriately scored tryptamine as an inhibitor.

CONCLUSIONS AND IMPLICATIONS

The pharmacophore model for the proton-antiporter inhibitors was a good predictor of known inhibitors and allowed us to identify new good inhibitors. This model marks a new step towards the discovery of this drug/proton antiporter and will be of great use for the discovery and design of potent inhibitors that could potentially help to assess and validate its pharmacological role in drug addiction in vivo.

A polyspecific drug/proton antiporter mediates diphenhydramine and clonidine transport at the mouse blood-retinal barrier

BACKGROUND AND PURPOSE

Transporters at the blood-retinal barrier (BRB), as at the blood-brain barrier (BBB), regulate the distribution of compounds into the neural parenchyma. However, the expression of BRB transporters and their quantitative impact in vivo are still poorly understood.

EXPERIMENTAL APPROACH

Clonidine and diphenhydramine are substrates of a novel BBB drug/proton-antiporter. We evaluated their transport at the BRB by in situ carotid perfusion in wild-type or knocked-out mice for Oct1-3 (Slc22a1-3).

KEY RESULTS

At pharmacological exposure levels, carrier-mediated BRB influx was 2 and 12 times greater than the passive diffusion rate for clonidine and diphenhydramine, respectively. Functional identification demonstrated the involvement of a high-capacity potassium- and sodium-independent proton-antiporter that shared the features of the previously characterized clonidine, diphenhydramine and cocaine BBB transporter. The functional characterization suggests that SLC transporters Oct1-3, Mate1 (Slc47a1) and Octn1-2 (Slc22a4-5) are not involved. Melanin/retinal toxic drugs like antimalarials (amodiaquine, quinine), quinidine and tricyclic antidepressants (imipramine) acted as inhibitors of this proton-antiporter. The endogenous indole derivative tryptamine inhibited the transporter, unlike 5-HT (serotonin), dopamine or L-DOPA. Trans-stimulation experiments with [(3) H]-clonidine at the BRB indicated that diphenhydramine, nicotine, oxycodone, naloxone, tramadol, 3,4-methylenedioxyamphetamine (MDMA, ecstasy), heroin, methadone and verapamil are common substrates.

CONCLUSIONS AND IMPLICATIONS

A proton-antiporter is physiologically involved in the transport of clonidine and diphenhydramine and is quantitatively more important than their passive diffusion flux at the mouse BRB. The features of this molecularly unidentified transporter highlight its importance in regulating drug delivery at the retina and suggest that it has the capacity to handle several drugs.

Influence of P-Glycoprotein Inhibition or Deficiency at the Blood-Brain Barrier on (18)F-2-Fluoro-2-Deoxy-D-glucose ( (18)F-FDG) Brain Kinetics

The fluorinated D-glucose analog (18)F-2-fluoro-2-deoxy-D-glucose ((18)F-FDG) is the most prevalent radiopharmaceutical for positron emission tomography (PET) imaging. P-Glycoprotein's (P-gp, MDR1, and ABCB1) function in various cancer cell lines and tumors was shown to impact (18)F-FDG incorporation, suggesting that P-gp function at the blood-brain barrier may also modulate (18)F-FDG brain kinetics. We tested the influence of P-gp inhibition using the cyclosporine analog valspodar (PSC833; 5 μM) on the uptake of (18)F-FDG in standardized human P-gp-overexpressing cells (MDCKII-MDR1). Consequences for (18)F-FDG brain kinetics were then assessed using (i) (18)F-FDG PET imaging and suitable kinetic modelling in baboons without or with P-gp inhibition by intravenous cyclosporine infusion (15 mg kg(-1) h(-1)) and (ii) in situ brain perfusion in wild-type and P-gp/Bcrp (breast cancer resistance protein) knockout mice and controlled D-glucose exposure to the brain. In vitro, the time course of (18)F-FDG uptake in MDR1 cells was influenced by the presence of valspodar in the absence of D-glucose but not in the presence of high D-glucose concentration. PET analysis revealed that P-gp inhibition had no significant impact on estimated brain kinetics parameters K 1, k 2, k 3, V T , and CMRGlc. The lack of P-gp effect on in vivo (18)F-FDG brain distribution was confirmed in P-gp/Bcrp-deficient mice. P-gp inhibition indirectly modulates (18)F-FDG uptake into P-gp-overexpressing cells, possibly through differences in the energetic cell level state. (18)F-FDG is not a P-gp substrate at the BBB and (18)F-FDG brain kinetics as well as estimated brain glucose metabolism are influenced by neither P-gp inhibition nor P-gp/Bcrp deficiencies in baboon and mice, respectively.

Carrier-mediated cocaine transport at the blood-brain barrier as a putative mechanism in addiction liability

BACKGROUND

The rate of entry of cocaine into the brain is a critical factor that influences neuronal plasticity and the development of cocaine addiction. Until now, passive diffusion has been considered the unique mechanism known by which cocaine crosses the blood-brain barrier.

METHODS

We reassessed mechanisms of transport of cocaine at the blood-brain barrier using a human cerebral capillary endothelial cell line (hCMEC/D3) and in situ mouse carotid perfusion.

RESULTS

Both in vivo and in vitro cocaine transport studies demonstrated the coexistence of a carrier-mediated process with passive diffusion. At pharmacological exposure level, passive diffusion of cocaine accounted for only 22.5% of the total cocaine influx in mice and 5.9% in hCMEC/D3 cells, whereas the carrier-mediated influx rate was 3.4 times greater than its passive diffusion rate in vivo. The functional identification of this carrier-mediated transport demonstrated the involvement of a proton antiporter that shared the properties of the previously characterized clonidine and nicotine transporter. The functionnal characterization suggests that the solute carrier (SLC) transporters Oct (Slc22a1-3), Mate (Slc47a1) and Octn (Slc22a4-5) are not involved in the cocaine transport in vivo and in vitro. Diphenhydramine, heroin, tramadol, cocaethylene, and norcocaine all strongly inhibited cocaine transport, unlike benzoylecgonine. Trans-stimulation studies indicated that diphenhydramine, nicotine, 3,4-methylenedioxyamphetamine (ecstasy) and the cathinone compound 3,4-methylenedioxypyrovalerone (MDPV) were also substrates of the cocaine transporter.

CONCLUSIONS

Cocaine transport at the BBB involves a proton-antiporter flux that is quantitatively much more important than its passive diffusion. The molecular identification and characterization of this transporter will provide new tools to understand its role in addictive mechanisms.

Human ABC transporters at blood-CNS interfaces as determinants of CNS drug penetration

Since the discovery of P-glycoprotein (P-gp) in brain microvessels composing the human blood-brain barrier (BBB), ATP-binding cassette (ABC) transporters have been recognized as bottlenecks in the development and delivery of neuropharmaceuticals. ABC transporters are expressed predominately at the plasma luminal membrane of brain capillary endothelial cells. These ABC transporters are responsible for the efflux of their substrates from the endothelial cells to the bloodstream against the concentration gradient and thus limit the entry of some drugs within the central nervous system (CNS). Advanced quantitative molecular biology tools allowed gene and protein quantification of the components of microvessels isolated from different species including human. Recently, positron emission tomography using radiolabelled probes that are substrates of ABC transporters allowed the determination of their functional activity at the human BBB. Here, we summarized new information regarding the relative expression, substrate recognition pattern for CNS drugs and functional activity of ABC transporters that are quantitatively expressed at the human BBB.

Hypoxia interferes with aryl hydrocarbon receptor pathway in hCMEC/D3 human cerebral microvascular endothelial cells

The expression of aryl hydrocarbon receptor (AhR) transcription factor was detected at transcript level in freshly isolated human brain microvessels and in the hCMEC/D3 human cerebral microvascular endothelial cell line. Recent studies have demonstrated that AhR pathway is able to crosstalk with other pathways such as hypoxia signaling pathway. Therefore, we used the hCMEC/D3 cell line to investigate the potential crosstalk between AhR and hypoxia signaling pathways. First, we performed two different hypoxia-like procedures in hCMEC/D3 cells; namely, exposition of cells to 150 μM deferoxamine or to glucose and oxygen deprivation for 6 h. These two procedures led to hypoxia-inducible factor (HIF)-1α and HIF-2α proteins accumulation together with a significant induction of the two well-known hypoxia-inducible genes VEGF and GLUT-1. Both HIF-1α and -2α functionally mediated hypoxia response in the hCMEC/D3 cells. Then, we observed that a 6 h exposure to 25 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin, a strong AhR ligand, up-regulated CYP1A1 and CYP1B1 expression, and that this effect was AhR dependent. Regarding AhR and hypoxia crosstalk, our experiments revealed that an asymmetric interference between these two pathways effectively occurred in hCMEC/D3 cells: hypoxia pathway interfered with AhR signaling but not the other way around. We studied the putative crosstalk of AhR and hypoxia pathways in hCMEC/D3 human cerebral microvascular endothelial cells. While hypoxia decreased the expression of the two AhR target genes CYP1A1 and CYP1B1, AhR activation results in no change in hypoxia target gene expression. This is the first sign of AhR and hypoxia pathway crosstalk in an in vitro model of the human cerebral endothelium.

Comparing translational population-PBPK modelling of brain microdialysis with bottom-up prediction of brain-to-plasma distribution in rat and human

The prediction of brain extracellular fluid (ECF) concentrations in human is a potentially valuable asset during drug development as it can provide the pharmacokinetic input for pharmacokinetic-pharmacodynamic models. This study aimed to compare two translational modelling approaches that can be applied at the preclinical stage of development in order to simulate human brain ECF concentrations. A population-PBPK model of the central nervous system was developed based on brain microdialysis data, and the model parameters were translated to their corresponding human values to simulate ECF and brain tissue concentration profiles. In parallel, the PBPK modelling software Simcyp was used to simulate human brain tissue concentrations, via the bottom-up prediction of brain tissue distribution using two different sets of mechanistic tissue composition-based equations. The population-PBPK and bottom-up approaches gave similar predictions of total brain concentrations in both rat and human, while only the population-PBPK model was capable of accurately simulating the rat ECF concentrations. The choice of PBPK model must therefore depend on the purpose of the modelling exercise, the in vitro and in vivo data available and knowledge of the mechanisms governing the membrane permeability and distribution of the drug.

KCNH2 polymorphism and methadone dosage interact to enhance QT duration

BACKGROUND

Many drugs increase the duration of the QT interval of patients, potentially leading to harmful effects such as polymorphic ventricular arrhythmias. Most of these drugs do so by inhibiting the rapid component IKr of the delayed rectifier potassium current IK. Methadone is the most prescribed heroin maintenance treatment and is known to inhibit the cardiac potassium channel hERG, which recapitulates IKr. In order to evaluate if any polymorphism of potassium channels' genes could explain some of the "idiosyncratic" QT prolongations observed in patients treated with methadone, we tested the association between KCNE1, KCNE2, and KCNH2 polymorphism and the QT interval prolongation in those patients, controlling for other variables associated with a decrease of the repolarizing reserve.

METHODS

A cohort of 82 patients treated with stable dosage of methadone (mean dosage 65 mg/d) for at least three months was genotyped for five polymorphisms in KCNE1, KCNE2 and KCNH2 genes and had their corrected QT (QTc) assessed.

RESULTS

The mean QTc interval was 415±34ms. In a linear regression model, longer QTc interval was associated with methadone dosage and with one genetic factor. Each copy of a Lys allele at codon 897 of KCNH2, the gene that encodes the cardiac potassium voltage-gated channel hERG, was associated with a 15.4ms longer QTc (95% CI [4.6-26.2]; p=0.001).

CONCLUSION

KCNH2 genotyping may be relevant in the analysis of cumulative risk factors for QT prolongation in patients on methadone maintenance treatment.

Altered cerebral vascular volumes and solute transport at the blood-brain barriers of two transgenic mouse models of Alzheimer's disease

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.

Oatp1a4 and an L-thyroxine-sensitive transporter mediate the mouse blood-brain barrier transport of amyloid-β peptide

The influx of amyloid-β peptide (Aβ) across the blood-brain barrier is partly mediated by the receptor for advanced glycation end products (RAGE). 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.

[¹¹C]befloxatone brain kinetics is not influenced by Bcrp function at the blood-brain barrier: a PET study using Bcrp TGEM knockout rats

Knockout (KO) animals are useful tools with which to assess the interplay between P-glycoprotein (P-gp; Abcb1) and the breast cancer resistance protein (Bcrp, Abcg2), two major ABC-transporters expressed at the blood-brain barrier (BBB). However, one major drawback of such deficient models is the possible involvement of compensation between transporters. In the present study, P-gp and Bcrp distribution in the brain as well as P-gp expression levels at the BBB were compared between the Bcrp TGEM KO rat model and the wild-type (WT) strain. Therefore, we used confocal microscopy of brain slices and western blot analysis of the isolated brain microvessels forming the BBB. This deficient rat model was used to assess the influence of Bcrp on the brain and peripheral kinetics of its substrate [(11)C]befloxatone using positron emission tomography (PET). The influence of additional P-gp inhibition was tested using elacridar (GF120918) 2 mg/kg in Bcrp KO rats. The distribution pattern of P-gp in the brain as well as P-gp expression levels at the BBB was similar in Bcrp-deficient and WT rats. Brain and peripheral kinetics of [(11)C]befloxatone were not influenced by the lack of Bcrp. Neither was the brain uptake of [(11)C]befloxatone in Bcrp-deficient rats influenced by the inhibition of P-gp. In conclusion, the Bcrp-deficient rat strain, in which we detected no compensatory mechanism or modification of P-gp expression as compared to WT rats, is a suitable model to study Bcrp function separately from that of P-gp at the BBB. However, although selectively transported by BCRP in vitro, our results suggest that [(11)C]befloxatone PET imaging might not be biased by impaired function of this transporter in vivo.

Effects of selected OATP and/or ABC transporter inhibitors on the brain and whole-body distribution of glyburide

Glyburide (glibenclamide, GLB) is a widely prescribed antidiabetic with potential beneficial effects in central nervous system injury and diseases. In vitro studies show that GLB is a substrate of organic anion transporting polypeptide (OATP) and ATP-binding cassette (ABC) transporter families, which may influence GLB distribution and pharmacokinetics in vivo. In the present study, we used [(11)C]GLB positron emission tomography (PET) imaging to non-invasively observe the distribution of GLB at a non-saturating tracer dose in baboons. The role of OATP and P-glycoprotein (P-gp) in [(11)C]GLB whole-body distribution, plasma kinetics, and metabolism was assessed using the OATP inhibitor rifampicin and the dual OATP/P-gp inhibitor cyclosporine. Finally, we used in situ brain perfusion in mice to pinpoint the effect of ABC transporters on GLB transport at the blood-brain barrier (BBB). PET revealed the critical role of OATP on liver [(11)C]GLB uptake and its subsequent impact on [(11)C]GLB metabolism and plasma clearance. OATP-mediated uptake also occurred in the myocardium and kidney parenchyma but not the brain. The inhibition of P-gp in addition to OATP did not further influence [(11)C]GLB tissue and plasma kinetics. At the BBB, the inhibition of both P-gp and breast cancer resistance protein (BCRP) was necessary to demonstrate the role of ABC transporters in limiting GLB brain uptake. This study demonstrates that GLB distribution, metabolism, and elimination are greatly dependent on OATP activity, the first step in GLB hepatic clearance. Conversely, P-gp, BCRP, and probably multidrug resistance protein 4 work in synergy to limit GLB brain uptake.

Physiologically based pharmacokinetic modelling of drug penetration across the blood-brain barrier--towards a mechanistic IVIVE-based approach

Predicting the penetration of drugs across the human blood-brain barrier (BBB) is a significant challenge during their development. A variety of in vitro systems representing the BBB have been described, but the optimal use of these data in terms of extrapolation to human unbound brain concentration profiles remains to be fully exploited. Physiologically based pharmacokinetic (PBPK) modelling of drug disposition in the central nervous system (CNS) currently consists of fitting preclinical in vivo data to compartmental models in order to estimate the permeability and efflux of drugs across the BBB. The increasingly popular approach of using in vitro-in vivo extrapolation (IVIVE) to generate PBPK model input parameters could provide a more mechanistic basis for the interspecies translation of preclinical models of the CNS. However, a major hurdle exists in verifying these predictions with observed data, since human brain concentrations can't be directly measured. Therefore a combination of IVIVE-based and empirical modelling approaches based on preclinical data are currently required. In this review, we summarise the existing PBPK models of the CNS in the literature, and we evaluate the current opportunities and limitations of potential IVIVE strategies for PBPK modelling of BBB penetration.

Hurdles with using in vitro models to predict human blood-brain barrier drug permeability: a special focus on transporters and metabolizing enzymes

The penetration of drugs into the human brain through the blood-brain barrier (BBB) is a major obstacle limiting the development of successful neuropharmaceuticals. This restricted permeability is due to the delicate intercellular junctions, efflux transporters and metabolizing enzymes present at the BBB. The pharmaceutical industry and academic research relies heavily on permeability studies conducted in animals and in vitro models of the BBB. This text reviews the available animal and in vitro BBB models with special emphasis on the situation in freshly isolated human brain microvessels and the unique tightness between brain endothelial cells, drug transport pathways and metabolic capacity. We first outline the delicate structure of the intercellular junctions and the particular interaction between the brain endothelial cells and other components of the neurovascular unit. We then examine the differences in transporters and metabolizing enzymes between species and in vitro systems and those found in isolated brain microvessels. Finally, we review the possibilities of benchmarking in vitro models of the BBB in terms of gene and protein expression.

Quantitative targeted absolute proteomic analysis of transporters, receptors and junction proteins for validation of human cerebral microvascular endothelial cell line hCMEC/D3 as a human blood-brain barrier model

Human cerebral microvascular endothelial cell line hCMEC/D3 is an established model of the human blood-brain barrier (BBB). The purpose of the present study was to determine, by means of quantitative targeted absolute proteomics, the protein expression levels in hCMEC/D3 cells of multiple transporters, receptors and junction proteins for comparison with our previously reported findings in isolated human brain microvessels. Among 91 target molecules, 12 transporters, 2 receptors, 1 junction protein and 1 membrane marker were present at quantifiable levels in plasma membrane fraction of hCMEC/D3 cells. ABCA2, MDR1, MRP4, BCRP, GLUT1, 4F2hc, MCT1, ENT1, transferrin and insulin receptors and claudin-5 were detected in both hCMEC/D3 cells and human brain microvessels. After normalization based on Na(+)/K(+) ATPase expression, the differences in protein expression levels between hCMEC/D3 cells and human brain microvessels were within 4-fold for these proteins, with the exceptions of ENT1, transferrin receptor and claudin-5. ABCA8, LAT1, LRP1 and γ-GTP were below the limit of quantification in the cells, but were found in human brain microvessels. ABCA3, ABCA6, MRP1 and ATA1 were found only in hCMEC/D3 cells. Furthermore, compared with human umbilical vein endothelial cells (HUVECs) as reference nonbrain endothelial cells, MDR1 was found only in hCMEC/D3 cells, and GLUT1 expression was 15-fold higher in hCMEC/D3 cells than in HUVECs. In conclusion, this is the first study to examine the suitability and limitations of the hCMEC/D3 cell line as a BBB functional model in terms of quantitative expression levels of transporters, receptors and tight junction proteins.

Coexistence of passive and proton antiporter-mediated processes in nicotine transport at the mouse blood-brain barrier

Nicotine, the main tobacco alkaloid leading to smoking dependence, rapidly crosses the blood-brain barrier (BBB) to become concentrated in the brain. Recently, it has been shown that nicotine interacts with some organic cation transporters (OCT), but their influence at the BBB has not yet been assessed in vivo. In this study, we characterized the transport of nicotine at the mouse luminal BBB by in situ brain perfusion. Its influx was saturable and followed the Michaelis-Menten kinetics (K(m)=2.60 mM, V(max)=37.60 nmol/s/g at pH 7.40). At its usual micromolar concentrations in the plasma, most (79%) of the net transport of nicotine at the BBB was carrier-mediated, while passive diffusion accounted for 21%. Studies on knockout mice showed that the OCT Oct1-3, P-gp, and Bcrp did not alter [(3)H]-nicotine transport at the BBB. Neither did inhibiting the transporters Mate1, Octn, or Pmat. The in vivo manipulation of intracellular and/or extracellular pH, the chemical inhibition profile, and the trans-stimulation experiments demonstrated that the nicotine transporter at the BBB shared the properties of the clonidine/proton antiporter. The molecular features of this proton-coupled antiporter have not yet been identified, but it also transports diphenhydramine and tramadol and helps nicotine cross the BBB at a faster rate and to a greater extent. The pharmacological inhibition of this nicotine/proton antiporter could represent a new strategy to reduce nicotine uptake by the brain and thus help curb addiction to smoking.

Expression and induction by dexamethasone of ABC transporters and nuclear receptors in a human T-lymphocyte cell line

The efficacy of drugs acting within lymphocytes, like antiretroviral drugs in the treatment of HIV infection, depends on their intracellular concentrations modulated by efflux proteins like ABCB1 (P-glycoprotein). In lymphocytes, two glucocorticoids, prednisone and prednisolone, have been shown to induce ABCB1 activity. Yet, no data exist regarding dexamethasone (DEX). We report the modulation of ABC transporters and nuclear receptors' expression by DEX in a commonly used model of human lymphocytes. CCRF-CEM cells were exposed to DEX (100 nM, 2 μM) for 24 to 72 hours. ABCB1 activity was measured using DiOC(6) efflux in flow cytometry. Gene expression levels were quantified by qRT-PCR. ABCB1 activity and mRNA expression increased with DEX concentrations and incubation times. DEX (1 μM, 24 h) increased significantly ABCB1 and GR mRNA expression levels by around 8- and 3.5-fold, respectively (P<10(-6)). ABCB1 induction by DEX in CCRF-CEM cells suggests a potential risk of interaction in lymphocytes when associating DEX to ABCB1 substrates in antiretroviral multitherapies in vivo.

[Recent advances in quantitative proteomics as a sensitive tool to quantify drug transporters and drug metabolizing enzymes at the human blood-brain barrier]

Since its discovery at the beginning of the 20th century, the blood-brain barrier (BBB) has been considered for a long time as a "physical barrier" able to limit brain distribution of highly molecular weight and/or polar compounds. This early concept of an anatomical barrier between the blood and the brain was supported by the finding of unique tight junctions between the brain endothelial cells so that they formed a continuous wall preventing the paracellular diffusion of solutes. In the middle of the 50's, BBB has been proposed as a "biochemical barrier" able to control the supply of brain to essential nutriments. More recently, BBB was evidenced as a key element in controlling effects of central nervous system drugs, since it plays a critical role in the uptake and efflux of drugs from the blood to the brain, or vice versa, hence affecting their concentrations and effects in the central nervous system (CNS). The BBB has therefore been more recently defined as a "pharmacological barrier" since the endothelial cells were found to contain a range of metabolizing enzymes and transporters that control the rate and extent of drugs reaching the brain parenchyma via transcellular pathway. The emergence of new quantitative proteomic approaches allows quantifying these transporters and enzymes at the BBB, opening the way to identify new drugs that may be targeted to the brain.

Induction of P-glycoprotein and Bcrp at the rat blood-brain barrier following a subchronic morphine treatment is mediated through NMDA/COX-2 activation

Subchronic morphine treatment induces P-glycoprotein (P-gp) up-regulation at the blood-brain barrier. This study investigates the rate and extent to which P-gp and breast cancer-resistance protein (Bcrp) increase at the rat blood-brain barrier following subchronic morphine treatment. Rats were given increasing doses of morphine (10-40 mg/kg) or saline i.p. twice daily for 5 days. The brain cortex large vessels and microvessels were then mechanical isolated 6, 9, 12, 24, and 36 h after the last injection. The gene and protein expression of P-gp and Bcrp in morphine-treated and control rats were compared by qRT-PCR and western blotting. The levels of Mdr1a and Bcrp mRNAs were not significantly modified 6 h post morphine, but the Mdr1a mRNA increased 1.4-fold and Bcrp mRNA 2.4-fold at 24 h. P-gp and Bcrp protein expression in brain microvessels was unchanged 6 h post morphine and increased 1.5-fold at 24 h. This effect was more pronounced in large vessels than in microvessels. However, extracellular morphine concentrations of 0.01-10 μM did not modify the expressions of the MDR1 and BCRP genes in hCMEC/D3 human endothelial brain cells in vitro. MK-801 (NMDA antagonist) and meloxicam (cyclo-oxygenase-2 inhibitor) given after morphine treatment completely blocked P-gp and Bcrp up-regulation. Interestingly, misoprostol and iloprost, two well-known agonists of prostaglandin E2 receptors induced both MDR1 and BCRP mRNA levels in hCMEC/D3. Thus, morphine does not directly stimulate P-gp and Bcrp expression by the brain endothelium, but glutamate released during morphine withdrawal may do so by activating the NMDA/cyclo-oxygenase-2 cascade.

Opioid transport by ATP-binding cassette transporters at the blood-brain barrier: implications for neuropsychopharmacology

Some of the ATP-binding cassette (ABC) transporters like P-glycoprotein (P-gp; ABCB1, MDR1), BCRP (ABCG2) and MRPs (ABCCs) that are present at the blood-brain barrier (BBB) influence the brain pharmacokinetics (PK) of their substrates by restricting their uptake or enhancing their clearance from the brain into the blood, which has consequences for their CNS pharmacodynamics (PD). Opioid drugs have been invaluable tools for understanding the PK-PD relationships of these ABC-transporters. The effects of morphine, methadone and loperamide on the CNS are modulated by P-gp. This review examines the ways in which other opioid drugs and some of their active metabolites interact with ABC transporters and suggests new mechanisms that may be involved in the variability of the response of the CNS to these drugs like carrier-mediated system belonging to the solute carrier (SLC) superfamily. Exposure to opioids may also alter the expression of ABC transporters. P-gp can be overproduced during morphine treatment, suggesting that the drug has a direct or, more likely, an indirect action. Variations in cerebral neurotransmitters during exposure to opioids and the release of cytokines during pain could be new endogenous stimuli affecting transporter synthesis. This review concludes with an analysis of the pharmacotherapeutic and clinical impacts of the interactions between ABC transporters and opioids.

Aryl hydrocarbon receptor-dependent upregulation of Cyp1b1 by TCDD and diesel exhaust particles in rat brain microvessels

Background

AhR activates the transcription of several target genes including CYP1B1. Recently, we showed CYP1B1 as the major cytochrome P450 (CYP) enzyme expressed in human brain microvessels. Here, we studied the effect of AhR activation by environmental pollutants on the expression of Cyp1b1 in rat brain microvessels.

Methods

Expression of AhR and Cyp1b1 was detected in isolated rat brain microvessels. AhR was immunovisualised in brain microvessel endothelial cells. The effect of AhR ligands on Cyp1b1 expression was studied using isolated brain microvessels after ex vivo and/or in vivo exposure to TCDD, heavy hydrocarbons containing diesel exhaust particles (DEP) or Δ⁹-tetrahydrocannabinol (Δ⁹-THC).

Results

After ex vivo exposure to TCDD (a highly potent AhR ligand) for 3 h, Cyp1b1 expression was significantly increased by 2.3-fold in brain microvessels. A single i.p. dose of TCDD also increased Cyp1b1 transcripts (22-fold) and Cyp1b1 protein (2-fold) in rat brain microvessels at 72 h after TCDD. Likewise, DEP treatment (in vivo and ex vivo) strongly induced Cyp1b1 protein in brain microvessels. DEP-mediated Cyp1b1 induction was inhibited by actinomycin D, cycloheximide, or by an AhR antagonist. In contrast, a sub-chronic in vivo treatment with Δ⁹-THC once daily for 7 seven days had no effect on Cyp1b1 expression

Conclusions

Our results show that TCDD and DEP strongly induced Cyp1b1 in rat brain microvessels, likely through AhR activation.