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

Resveratrol metabolism in a non-human primate, the grey mouse lemur (Microcebus murinus), using ultra-high-performance liquid chromatography-quadrupole time of flight.

The grey mouse lemur (Microcebus murinus) is a non-human primate used to study the ageing process. Resveratrol is a polyphenol that may increase lifespan by delaying age-associated pathologies. However, no information about resveratrol absorption and metabolism is available for this primate. Resveratrol and its metabolites were qualitatively and quantitatively analyzed in male mouse-lemur plasma (after 200 mg.kg-1 of oral resveratrol) by ultra-high performance liquid chromatography (UHPLC), coupled to a quadrupole-time-of-flight (Q-TOF) mass spectrometer used in full-scan mode. Data analyses showed, in MSE mode, an ion common to resveratrol and all its metabolites: m/z 227.072, and an ion common to dihydro-resveratrol metabolites: m/z 229.08. A semi-targeted study enabled us to identify six hydrophilic resveratrol metabolites (one diglucurono-conjugated, two monoglucurono-conjugated, one monosulfo-conjugated and two both sulfo- and glucurono-conjugated derivatives) and three hydrophilic metabolites of dihydro-resveratrol (one monoglucurono-conjugated, one monosulfo-conjugated, and one both sulfo- and glucurono-conjugated derivatives). The presence of such metabolites has been already detected in the mouse, rat, pig, and humans. Free resveratrol was measurable for several hours in mouse-lemur plasma, and its two main metabolites were trans-resveratrol-3-O-glucuronide and trans-resveratrol-3-sulfate. Free dihydro-resveratrol was not measurable whatever the time of plasma collection, while its hydrophilic metabolites were present at 24 h after intake. These data will help us interpret the effect of resveratrol in mouse lemurs and provide further information on the inter-species characteristics of resveratrol metabolism

LC–MS/MS-based quantification of efflux transporter proteins at the BBB

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Targeted unlabeled multiple reaction monitoring analysis of cell markers for the study of sample heterogeneity in isolated rat brain cortical microvessels

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Chemical structure of A: <i>Trans</i>-resveratrol; B: <i>trans</i>-resveratrol-¹³C₆; C: <i>trans</i>-resveratrol-3-sulfate (R1 = R2 = R3 = R4 = H) or <i>trans</i>-resveratrol-3-sulfate-D4 (R1 = R2 = R3 = R4 = D); D: <i>trans</i>-resveratrol-3-O-ß-D-glucuronide (R1 = R2 = R3 = R4 = H) or <i>trans</i>-resveratrol-3-O-ß-D-glucuronide-D₄ (R1 = R2 = R3 = R4 = D); E: <i>trans</i>-resveratrol-4′-O-ß-D-glucuronide (R1 = R2 = R3 = R4 = H) or <i>trans</i>-resveratrol-4′-O-ß-D-glucuronide-D₄ (R1 = R2 = R3 = R4 = D).

<p>Chemical structure of A: <i>Trans</i>-resveratrol; B: <i>trans</i>-resveratrol-¹³C₆; C: <i>trans</i>-resveratrol-3-sulfate (R1 = R2 = R3 = R4 = H) or <i>trans</i>-resveratrol-3-sulfate-D4 (R1 = R2 = R3 = R4 = D); D: <i>trans</i>-resveratrol-3-O-ß-D-glucuronide (R1 = R2 = R3 = R4 = H) or <i>trans</i>-resveratrol-3-O-ß-D-glucuronide-D₄ (R1 = R2 = R3 = R4 = D); E: <i>trans</i>-resveratrol-4′-O-ß-D-glucuronide (R1 = R2 = R3 = R4 = H) or <i>trans</i>-resveratrol-4′-O-ß-D-glucuronide-D₄ (R1 = R2 = R3 = R4 = D).</p

Low- and high-collision energy spectra of ions specific to resveratrol-glucuronide, <i>m/z</i> 403.102.

<p>Low- and high-collision energy spectra of ions specific to resveratrol-glucuronide, <i>m/z</i> 403.102.</p

Concentrations of <i>trans</i>-resveratrol and its hydrophilic metabolites and hydrophilic metabolites of dihydro-resveratrol (DHR).

<p>Mean values in µmol.L⁻¹. Values expressed as “<i>trans</i>-resveratrol-4′-O-ß-glucuronide equivalent” for <i>trans</i>-resveratrol glucuronide sulfate and DHR-glucuronide sulfate; as “<i>trans</i>-resveratrol-3-O-ß-glucuronide equivalent” for the DHR-glucuronide and as “<i>trans</i>-resveratrol-3-sulfate equivalent” for the DHR-sulfate. CV% between mouse lemurs (round brackets), range [square brackets]. There were three determinations for each concentration. <i>n</i>: sample size.</p><p>LLOQ: lower limit of quantification.</p

<i>m/z</i> average and accuracy (ppm) for precursor and daughter ions of resveratrol and their metabolites.

<p>RGS = <i>trans</i>-resveratrol-glucuronide-sulfate; 4′RG = <i>trans</i>-resveratrol-4′-O-ß-glucuronide; 3RG = <i>trans</i>-resveratrol-3-O-ß-glucuronide; RS = <i>trans</i>-resveratrol-sulfate, R = resveratrol; DHRGS = DHR-glucuronide-sulfate; DHRG = DHR-glucuronide; DHRS = DHR-sulfate.</p><p>Standard samples: 3×5 injections; plasma samples: 17×2 injections.</p><p><i>n</i>: Number of injections where an ion was found.</p

High-collision energy spectrum of ions specific to resveratrol, <i>m/z</i> 227.072, showing the daughter ions formed.

<p>High-collision energy spectrum of ions specific to resveratrol, <i>m/z</i> 227.072, showing the daughter ions formed.</p

Chromatograms: variations in the intensity of <i>m/z</i> 227.07 (a) and <i>m/z</i> 229.087 (b) vs. time.

<p><b>a</b>: Time 2 h after intake of resveratrol. High-collision energy spectrum at 2.05 min. <b>b</b>: Time 24 h after intake of resveratrol. High-collision energy spectrum at 2.11 min.</p