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ABCG2/BCRP is an ABC transporter that plays an important role in tissue protection by exporting endogenous substrates and xenobiotics. ABCG2 is of major interest due to its ...involvement in multidrug resistance (MDR), and understanding its complex efflux mechanism is essential to preventing MDR and drug-drug interactions (DDI). ABCG2 export is characterized by two major conformational transitions between inward- and outward-facing states, the structures of which have been resolved. Yet, the entire transport cycle has not been characterized to date. Our study bridges the gap between the two extreme conformations by studying connecting pathways. We developed an innovative approach to enhance molecular dynamics simulations, ‘kinetically excited targeted molecular dynamics’, and successfully simulated the transitions between inward- and outward-facing states in both directions and the transport of the endogenous substrate estrone 3-sulfate. We discovered an additional pocket between the two substrate-binding cavities and found that the presence of the substrate in the first cavity is essential to couple the movements between the nucleotide-binding and transmembrane domains. Our study shed new light on the complex efflux mechanism, and we provided transition pathways that can help to identify novel substrates and inhibitors of ABCG2 and probe new drug candidates for MDR and DDI.
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.
WHAT WE ALREADY KNOW ABOUT THIS TOPICNeuropathic pain, which presents abnormal pain manifestations including allodynia and hyperalgesia, is associated with central sensitization involving ...N-methyl-D-aspartate receptorsIn the freeze-injury hyperalgesia model, a cold burn leads to development of both primary hyperalgesia and secondary hyperalgesia, which develops away from the site of injury without apparent tissue modification, and is associated with central sensitization and activation of N-methyl-D-aspartate receptors in the spinal cordDextromethorphan, which is an N-methyl-D-aspartate receptor antagonist, is antihyperalgesic in preclinical pain models
WHAT THIS ARTICLE TELLS US THAT IS NEWUsing the freeze-injury pain model in a randomized, double-blind, placebo-controlled crossover trial of 30-mg doses of oral dextromethorphan in 20 male volunteers, dextromethorphan was antihyperalgesic and reversed peripheral and central neuronal sensitizationBecause dextromethorphan had no intrinsic antinociceptive effect in acute pain on healthy skin, N-methyl-D-aspartate receptors may need to be sensitized by pain for dextromethorphan to be effective
BACKGROUND:Central pain sensitization is often refractory to drug treatment. Dextromethorphan, an N-methyl-D-aspartate receptor antagonist, is antihyperalgesic in preclinical pain models. The hypothesis is that dextromethorphan is also antihyperalgesic in humans.
METHODS:This randomized, double-blind, placebo-controlled, crossover study explores the antihyperalgesic effect of single and repeated 30-mg dose of oral dextromethorphan in 20 volunteers, using the freeze-injury pain model. This model leads to development of primary and secondary hyperalgesia, which develops away from the site of injury and is associated with central sensitization and activation of N-methyl-D-aspartate receptor in the spinal cord. The primary outcome was antihyperalgesia calculated with the area under the curve of the percentage change in mechanical pain threshold (electronic von Frey) on the area of secondary hyperalgesia. The secondary outcomes were mechanical pain threshold on the area of primary hyperalgesia and cognitive (reaction time) effect.
RESULTS:Single 30-mg results are reported. Antihyperalgesia (% · min) is significantly higher on the area of secondary hyperalgesia with dextromethorphan than placebo (median interquartile range3,029 746; 6,195 vs. 710 –3,248; 4,439, P = 0.009, Hedge’s g = 0.8, 95% CI 0.1; 1.4). On primary hyperalgesia area, mechanical pain threshold 2 h after drug intake is significantly higher with dextromethorphan (P = 0.011, Hedge’s g = 0.63, 95% CI 0.01; 1.25). No difference in antinociception is observed after thermal painful stimuli on healthy skin between groups. Reaction time (ms) is shorter with placebo than with dextromethorphan (median interquartile range21.6 –37.4; 0.1 vs. –1.2 –24.3; 15.4, P = 0.015, Hedge’s g = 0.75, 95% CI 0.12; 1.39). Nonserious adverse events occurrence (15%, 3 of 20 volunteers) was similar in both groups.
CONCLUSIONS:This study shows that low-dose (30-mg) dextromethorphan is antihyperalgesic in humans on the areas of primary and secondary hyperalgesia and reverses peripheral and central neuronal sensitization. Because dextromethorphan had no intrinsic antinociceptive effect in acute pain on healthy skin, N-methyl-D-aspartate receptor may need to be sensitized by pain for dextromethorphan to be effective.
The number of reports on baclofen intoxication has increased in recent years. Here we report the case of a 4-year-old boy in deep coma who was referred to the pediatric intensive care unit. The ...patient was intubated and mechanically ventilated. A computerized tomography scan without contrast showed a collapsed appearance of the ventricular system suggesting diffuse cerebral edema. A multichannel electroencephalogram registered 6 h after admission showed a very slow and ample continuous pattern, without structure, nonreactive to stimulations, expressing diffuse and severe nonspecific cerebral pain. A targeted analysis to determine the baclofen plasma levels was performed. Test results of plasma samples were highly positive for baclofen (2009 ng/mL). Following 36 h of mechanical ventilation, the patient rapidly regained consciousness and recovered normal neurological behavior. The present case demonstrates the importance of considering baclofen overdosage in cases of deep coma with areflexia, and emphasizes the importance of warning parents about the potential toxicity of baclofen when prescribing the drug to a family member. A review of the literature on pediatric baclofen overdose is included.
Abstract Objectives ABC transporters in the human placenta play a major role in protecting the fetus against potential toxic drugs. The glucocorticoid dexamethasone has been shown to induce ABCB1 ...expression in enterocytes and hepatocytes. However, in placental cells, little data exists either for dexamethasone, betamethasone or prednisone while these three glucocorticoids may be used during pregnancy. We investigated the modulation of placental ABC transporter and nuclear receptor expression by these drugs. Methods Cytotrophoblasts were isolated from normal full-term placentas. We first assessed the influence of spontaneous syncytialization on transporter and nuclear receptor gene expression by taking samples of cytotrophoblasts after 24, 48 and 72 h of cell culture ( n = 7 placentas). Incubations were then conducted with dexamethasone (50 nM–1 μM), betamethasone (20–400 nM) and prednisone (50 nM–1 μM) versus no drug for 24 h ( n = 6). mRNA expression was determined by qRT-PCR. Results Influence of syncytialization was observed only for ABCB1 , ABCC2 and ABCC5 gene expression between t = 24 and 48 h ( p < 0.05). Therefore, the following induction studies were conducted between t = 48 h and 72 h. Dexamethasone and betamethasone significantly induced ABCB1 gene expression by around 4-fold ( p < 0.01 and 0.001, respectively). In parallel, 100 nM betamethasone decreased the glucocorticoid receptor gene expression by 22% ( p < 0.01). Prednisone showed no effect on transporter or receptor expression. Conclusions These results suggest that dexamethasone or betamethasone administration may decrease the maternal–fetal transfer of an associated treatment being ABCB1 substrate, which may be either protective or deleterious for the fetus depending on the treatment's therapeutic aim.
Purpose
Lithium (Li), the first-line treatment of bipolar disorder, was first developed as an immediate-release form with a routine therapeutic drug monitoring 12 h after the last dose. In Europe, ...the most commonly prescribed form is a sustained release (srLi). Yet no pharmacokinetics (PK) study has been published of srLi, administered once a day, in adults. The present study describes srLi PK in the serum and erythrocytes of bipolar patients.
Methods
To assess srLi PK, we studied prospectively 17 French bipolar patients on a median dose of 1000 mg (600–1600) for at least 2 years. Serum (S), erythrocyte (E) concentrations, and urinary (U) amount were collected over 8 h after 15 days of morning intake using monitoring electronic medical system (MEMs). Population PK parameters were estimated using the SAEM algorithm (MONOLIX 4.3.3 software).
Results
Using a population approach, we built a PK population model of srLi including one S compartment (
V
S
= 23.0 L, Cl
S
= 1.21 L h
−1
), one E compartment (
V
E
= 64.7 L, Cl
SE
= 3.63 L h
−1
, Cl
ES
= 9.46 L h
−1
), and one U compartment (
F
= 0.62) and estimate the ratio of concentrations to Li in E over S at 0.38 with 27% between-subject variability.
Conclusion
This is a PK model of srLi once a day in bipolar patients using a population approach simultaneously describing Li concentrations in serum, erythrocytes, and urine which provide an estimate of the ratio of concentration in erythrocyte over serum and its between-subject variability (BSV).
The efficacy of drugs acting within lymphocytes depends on their intracellular concentrations, which could be modulated by membrane efflux transporters including P-glycoprotein (P-gp), encoded by the
...MDR1 gene. In particular, P-gp induction may compromise the efficacy of its substrates. Rifampicin and phenobarbital have been shown to induce P-gp in hepatic and intestinal cells through the activation of the nuclear receptors PXR and CAR. However, controversial data exist in human lymphocytes. We investigated the effect of these drugs on P-gp activity and expression in lymphocytes
in vitro and
ex vivo. CCRF-CEM cells and peripheral blood mononuclear cells (PBMCs) from healthy volunteers were incubated in the presence of rifampicin, phenobarbital, or without any drug. P-gp activity was measured by flow cytometry using DiOC
6 efflux.
MDR1,
PXR and
CAR mRNA expression were measured by quantitative RT-PCR. Neither P-gp activity nor
MDR1 mRNA expression were modified by rifampicin or phenobarbital both in CCRF-CEM cells and PBMCs. Moreover, P-gp protein expression at the membrane was neither detectable nor induced. The very weak
PXR and
CAR mRNA expression levels in these cells could partly explain these results. Therefore, P-gp induction by rifampicin and phenobarbital may play a negligible role in drug interactions occurring within lymphocytes.
P‐glycoprotein (P‐gp) is an efflux transporter that controls the intracellular concentrations of drugs. Human development may modulate P‐gp function. We investigated the effect of age on P‐gp ...activity and MDR1 gene expression in lymphocytes. We also assessed the influence of human immunodeficiency virus (HIV) infection. We used 3,3′‐diethyloxacarbocyanin iodide (DiOC6) efflux, estimated by flow cytometry, to quantify P‐gp activity in 94 children (age range, 0–18 years) and 25 adults. MDR1 gene expression was quantified using reverse transcription–PCR (RT‐PCR). In T and natural killer (NK) cell populations, P‐gp activity peaked at birth, decreased between the ages of 0 and 6 months, and stabilized between the ages of 6 months and 2 years (P < 10−6). These maturation profiles were also strongly correlated (r = 0.67, P < 10−6). HIV infection did not affect P‐gp activity in the lymphocytes of children. MDR1 gene expression was not influenced by age, nor was it correlated with P‐gp activity. The high levels of P‐gp activity observed in the lymphocytes of children ~6 months of age may affect the efficacy of intracellular drugs.
Clinical Pharmacology & Therapeutics (2009); 85, 3, 289–295 doi:10.1038/clpt.2008.221
Background: Opioids are widely used in pain management, acting via opioid receptors
and/or Toll-like receptors (TLR) present at the central nervous system (CNS). At the blood-brain
barrier (BBB), ...several influx and efflux transporters, such as the ATP-binding cassette (ABC)
P-glycoprotein (P-gp, ABCB1), Breast Cancer Resistance Protein (BCRP, ABCG2) and multidrug
resistance-associated proteins (MRP, ABCC) transporters, and solute carrier transporters (SLC), are
responsible for the transport of xenobiotics from the brain into the bloodstream or vice versa.
Objective: ABC transporters export several clinically employed opioids, altering their neuropharmacokinetics
and CNS effects. In this review, we explore the interactions between opioids
and ABC transporters, and decipher the molecular mechanisms by which opioids can modify their
expression at the BBB.
Results: P-gp is largely implicated in the brain-to-blood efflux of opioids, namely morphine and
oxycodone. Long-term exposure to morphine and oxycodone has proven to up-regulate the expression
of ABC transporters, such as P-gp, BCRP and MRPs, at the BBB, which may lead to increased
tolerance to the antinociceptive effects of such drugs. Recent studies uncover two mechanisms by
which morphine may up-regulate P-gp and BCRP at the BBB: 1) via a glutamate, NMDA-receptor
and COX-2 signaling cascade, and 2) via TLR4 activation, subsequent development of neuroinflammation,
and activation of NF-kB, presumably via glial cells.
Conclusion: The BBB-opioid interaction can culminate in bilateral consequences, since ABC
transporters condition the brain disposition of opioids, while opioids also affect the expression of
ABC transporters at the BBB, which may result in increased CNS drug pharmacoresistance.
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