Differences in the transport of the antiepileptic drugs phenytoin, levetiracetam and carbamazepine by human and mouse P-glycoprotein

Sex and the Kidney Drug-Metabolizing Enzymes and Transporters: Are Preclinical Drug Disposition Data Translatable to Humans?

Cross-species differences in drug transport and metabolism are linked to poor translation of preclinical pharmacokinetic and toxicology data to humans, often resulting in the failure of new chemical entities (NCEs) during clinical drug development. Specifically, inaccurate prediction of renal clearance and renal accumulation of NCEs due to differential abundance of enzymes and transporters in kidneys can lead to differences in pharmacokinetics and toxicity between experimental animals and humans. We carried out liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based protein quantification of 78 membrane drug-metabolizing enzymes and transporters (DMETs) in the kidney membrane fractions of humans, rats, and mice for characterization of cross-species and sex-dependent differences. In general, majority of DMET proteins were higher in rodents than in humans. Significant cross-species differences were observed in 30 out of 33 membrane DMET proteins quantified in all three species. Although no significant sex-dependent differences were observed in humans, the abundance of 28 and 46 membrane proteins showed significant sex dependence in rats and mice, respectively. These cross-species and sex-dependent quantitative abundance data are valuable for gaining a mechanistic understanding of drug renal disposition and accumulation. Further, these data can also be integrated into systems pharmacology tools, such as physiologically based pharmacokinetic models, to enhance the interpretation of preclinical pharmacokinetic and toxicological data.

Applicability of MDR1 Overexpressing Abcb1KO-MDCKII Cell Lines for Investigating In Vitro Species Differences and Brain Penetration Prediction

Implementing the 3R initiative to reduce animal experiments in brain penetration prediction for CNS-targeting drugs requires more predictive in vitro and in silico models. However, animal studies are still indispensable to obtaining brain concentration and determining the prediction performance of in vitro models. To reveal species differences and provide reliable data for IVIVE, in vitro models are required. Systems overexpressing MDR1 and BCRP are widely used to predict BBB penetration, highlighting the impact of the in vitro system on predictive performance. In this study, endogenous Abcb1 knock-out MDCKII cells overexpressing MDR1 of human, mouse, rat or cynomolgus monkey origin were used. Good correlations between ERs of 83 drugs determined in each cell line suggest limited species specificities. All cell lines differentiated CNS-penetrating compounds based on ERs with high efficiency and sensitivity. The correlation between in vivo and predicted Kp,uu,brain was the highest using total ER of human MDR1 and BCRP and optimized scaling factors. MDR1 interactors were tested on all MDR1 orthologs using digoxin and quinidine as substrates. We found several examples of inhibition dependent on either substrate or transporter abundance. In summary, this assay system has the potential for early-stage brain penetration screening. IC50 comparison between orthologs is complex; correlation with transporter abundance data is not necessarily proportional and requires the understanding of modes of transporter inhibition.

Application of a new MDCKII-MDR1 cell model to measure the extent of drug distribution in vitro at equilibrium for prediction of in vivo unbound brain-to-plasma drug distribution

INTRO

Reliable estimates of drug uptake from blood to brain parenchyma are crucial in CNS drug discovery and development. While in vivo Kp,uu,brain estimates are the gold standard for investigating brain drug disposition, animal usage is a limitation to high throughput application. This study investigates an in vitro model using P-gp expressing MDCKII-MDR1 cells for predicting in vivo brain drug penetration.

METHODS

In vitro equilibrium distribution studies were conducted in apical and basolateral solutions with high protein content to estimate Kp,brain and Kp,uu,brain values. The correlation between in vitro and in vivo Kp,brain values for a set of compounds was examined.

RESULTS

We observed a good correlation between in vitro and in vivo Kp,brain values (R2 = 0.69, Slope: 1.6), indicating that the in vitro model could predict in vivo drug brain penetration. The 'unilateral (Uni-L)' in vitro setup correctly classified 5 out of 5 unrestricted compounds and 3 out of 5 restricted compounds. Possible reasons for the observed disparities for some compounds have been discussed, such as difference in transport areas between in vitro and in vivo settings and effect of pH changes.

CONCLUSION

The in vitro assay setup developed in this study holds promise for predicting in vivo drug brain penetration in CNS drug discovery. The correlation between in vitro and in vivo Kp,brain values, underscores that the model may have potential for early-stage screening. With minor refinements, this in vitro approach could reduce the reliance on in vivo experiments, accelerating the pace of CNS drug discovery and promoting a more ethical research approach.

Characterization of P-glycoprotein orthologs from human, sheep, pig, dog, and cat

The ATP-binding cassette transporter P-glycoprotein (P-gp) limits the oral bioavailability of many drugs. Although P-gp has been well studied in humans and mice, little is known about the substrate specificities of many of its species orthologs. To address this, we performed in vitro analysis of P-gp transporter function using HEK293 cells stably expressing human, ovine, porcine, canine, and feline P-gp. We also employed a human physiologically based pharmacokinetic (PBPK) model to assess variations in digoxin exposure resulting from altered P-gp function. Compared to human P-gp, sheep P-gp had significantly less digoxin efflux (2.3-fold ±0.04 vs. 1.8-fold ±0.03, p < .0001) and all species orthologs had significantly less quinidine efflux compared with human P-gp (p < .05). Human P-gp also had significantly greater efflux of talinolol compared to sheep and dog P-gp (1.9-fold ±0.04 vs. 1.6-fold ±0.06, p = .003 and 1.6-fold ±0.05, p = .0002, respectively). P-gp expression protected all lines against paclitaxel-induced toxicity, with sheep P-gp being significantly less protective. The inhibitor verapamil demonstrated dose-dependent inhibition of all P-gp orthologs. Finally, a PBPK model showed digoxin exposure was sensitive to altered P-gp activity. Overall, our study found that species differences in this major drug transporter exist and that the appropriate species ortholog of P-gp should be evaluated during veterinary drug development.

Comprehensive Physiologically Based Pharmacokinetic Model to Assess Drug-Drug Interactions of Phenytoin

Regulatory agencies worldwide expect that clinical pharmacokinetic drug-drug interactions (DDIs) between an investigational new drug and other drugs should be conducted during drug development as part of an adequate assessment of the drug's safety and efficacy. However, it is neither time nor cost efficient to test all possible DDI scenarios clinically. Phenytoin is classified by the Food and Drug Administration as a strong clinical index inducer of CYP3A4, and a moderate sensitive substrate of CYP2C9. A physiologically based pharmacokinetic (PBPK) platform model was developed using GastroPlus® to assess DDIs with phenytoin acting as the victim (CYP2C9, CYP2C19) or perpetrator (CYP3A4). Pharmacokinetic data were obtained from 15 different studies in healthy subjects. The PBPK model of phenytoin explains the contribution of CYP2C9 and CYP2C19 to the formation of 5-(4'-hydroxyphenyl)-5-phenylhydantoin. Furthermore, it accurately recapitulated phenytoin exposure after single and multiple intravenous and oral doses/formulations ranging from 248 to 900 mg, the dose-dependent nonlinearity and the magnitude of the effect of food on phenytoin pharmacokinetics. Once developed and verified, the model was used to characterize and predict phenytoin DDIs with fluconazole, omeprazole and itraconazole, i.e., simulated/observed DDI AUC ratio ranging from 0.89 to 1.25. This study supports the utility of the PBPK approach in informing drug development.

Implications of BCRP modulation on PTZ-induced seizures in mice: Role of ko143 and metformin as adjuvants to lamotrigine

Blood-brain barrier (BBB) efflux transporters' overexpression hinders antiepileptic drug brain entry. Breast cancer resistance protein (BCRP) is a major BBB efflux transporter. In the present work, BCRP's role as a mechanism that might contribute to drug-resistant epilepsy (DRE) in a mouse model of acute seizures was studied with further assessment of the effect of its inhibition by ko143 and metformin (MET) on lamotrigine (LTG) bioavailability and efficacy. 42 male mice divided into 6 groups: G1: Normal control, G2: LTG-injected healthy mice: LTG 20 mg/kg i.p., G3: Acute seizures (A.S) mice: Pentylenetetrazole (PTZ) 50 mg/kg i.p., G4: LTG-treated A.S mice: LTG 20 mg/kg + PTZ 50 mg/kg i.p., G5: Ko143 + LTG treated A.S mice: Ko143 15 mg/kg i.p. before LTG + PTZ, G6: MET + LTG treated A.S mice: MET 200 mg/kg i.p. before LTG + PTZ. Seizures severity, serum, brain LTG, and brain BCRP were assessed. PTZ group experienced the highest seizure frequency and brain BCRP expression. Ko143 and MET groups showed a significant decrease in brain BCRP with subsequent improvement in brain LTG level and better seizure control. BCRP has a significant role in epilepsy resistance and its inhibition with ko143 or MET adds value to DRE management.

The efficacy of direct oral anticoagulants in patients on concomitant treatment with levetiracetam

Guidelines do not support the combination of direct oral anticoagulants (DOACs) and the antiepileptic drug levetiracetam, due to potential relevant P-glycoprotein (P-gp) mediated interaction that might result in decreased DOACs concentrations and increased thromboembolic risk. However, there is no systematic data on the safety of this combination. The aim of this study was to find patients concurrently treated with levetiracetam and DOAC, assess their plasma concentrations of DOAC, and the incidence of thromboembolic events. From our registry of patients on anticoagulation drugs we identified 21 patients concomitantly treated with levetiracetam and DOAC, 19 patients with atrial fibrillation and two patients with venous thromboembolism. Eight patients received dabigatran, 9 apixaban and 4 rivaroxaban. For each subject blood samples were collected for determination of trough DOAC and trough levetiracetam concentrations. The average age was 75 ± 9 years, 84% were males, HAS-BLED score was 1.8 ± 0.8, and in patients with atrial fibrillation CHA₂DS₂-VASc score was 4.6 ± 2.0. The average trough concentration level of levetiracetam was 31.0 ± 34.5 mg/L. Median trough concentrations of DOACs were for dabigatran 72 (range 25-386) ng/mL, for rivaroxaban 47 (range 19-75) ng/mL, and for apixaban 139 (range 36-302) ng/mL. During the observation period of 1388 ± 994 days none of the patients suffered a thromboembolic event. Our results did not demonstrate a reduction in DOACs plasma levels during levetiracetam treatment, suggesting that levetiracetam could not be an important P-gp inducer in humans. DOAC in combination with levetiracetam remained effective therapy to protect against thromboembolic events.

Differential Expression of ABC Transporter Genes in Brain Vessels vs. Peripheral Tissues and Vessels from Human, Mouse and Rat

BACKGROUND

ATP-binding cassette (ABC) transporters comprise a superfamily of genes encoding membrane proteins with nucleotide-binding domains (NBD). These transporters, including drug efflux across the blood-brain barrier (BBB), carry a variety of substrates through plasma membranes against substrate gradients, fueled by hydrolyzing ATP. The expression patterns/enrichment of ABC transporter genes in brain microvessels compared to peripheral vessels and tissues are largely uncharacterized.

METHODS

In this study, the expression patterns of ABC transporter genes in brain microvessels, peripheral tissues (lung, liver and spleen) and lung vessels were investigated using RNA-seq and Wes^TM analyses in three species: human, mouse and rat.

RESULTS

The study demonstrated that ABC drug efflux transporter genes (including ABCB1, ABCG2, ABCC4 and ABCC5) were highly expressed in isolated brain microvessels in all three species studied; the expression of ABCB1, ABCG2, ABCC1, ABCC4 and ABCC5 was generally higher in rodent brain microvessels compared to those of humans. In contrast, ABCC2 and ABCC3 expression was low in brain microvessels, but high in rodent liver and lung vessels. Overall, most ABC transporters (with the exception of drug efflux transporters) were enriched in peripheral tissues compared to brain microvessels in humans, while in rodent species, additional ABC transporters were found to be enriched in brain microvessels.

CONCLUSIONS

This study furthers the understanding of species similarities and differences in the expression patterns of ABC transporter genes; this is important for translational studies in drug development. In particular, CNS drug delivery and toxicity may vary among species depending on their unique profiles of ABC transporter expression in brain microvessels and BBB.

The role of the efflux transporter, P-glycoprotein, at the blood-brain barrier in drug discovery

The blood-brain barrier (BBB) expresses a high abundance of transporters, particularly P-glycoprotein (P-gp), that regulate endogenous and exogenous molecule uptake and removal of waste. This review discusses key drug metabolism and pharmacokinetic considerations for the efflux transporter P-gp at the BBB in drug discovery and development. We highlight the differences in P-gp expression and protein levels across species but the limited observations of species-specific substrates. Given the impact of age and disease on BBB biology, we summarise the modulation of P-gp for several neurological disorders and ageing and exemplify several disease-specific hurdles or opportunities for drug exposure in the brain. Furthermore, the review includes observations of CNS-related drug-drug interactions due to the inhibition or induction of P-gp at the BBB in animal studies and humans and the need for continued evaluation especially for compounds with a narrow therapeutic window. This review focusses primarily on small molecules but also considers the impact of new chemical entities, particularly beyond Ro5 molecules and their potential to be recognised as P-gp substrates as well as advanced drug delivery systems which offer an alternative approach to achieve and sustain central nervous system exposure.

Central Nervous System Distribution of the Ataxia-Telangiectasia Mutated Kinase Inhibitor AZD1390: Implications for the Treatment of Brain Tumors

Effective drug delivery to the brain is critical for the treatment of glioblastoma (GBM), an aggressive and invasive primary brain tumor that has a dismal prognosis. Radiation therapy, the mainstay of brain tumor treatment, works by inducing DNA damage. Therefore, inhibiting DNA damage response (DDR) pathways can sensitize tumor cells to radiation and enhance cytotoxicity. AZD1390 is an inhibitor of ataxia-telangiectasia mutated kinase, a critical regulator of DDR. Our in vivo studies in the mouse indicate that delivery of AZD1390 to the central nervous system (CNS) is restricted due to active efflux by P-glycoprotein (P-gp). The free fraction of AZD1390 in brain and spinal cord were found to be low, thereby reducing the partitioning of free drug to these organs. Coadministration of an efflux inhibitor significantly increased CNS exposure of AZD1390. No differences were observed in distribution of AZD1390 within different anatomic regions of CNS, and the functional activity of P-gp and breast cancer resistance protein also remained the same across brain regions. In an intracranial GBM patient-derived xenograft model, AZD1390 accumulation was higher in the tumor core and rim compared with surrounding brain. Despite this heterogenous delivery within tumor-bearing brain, AZD1390 concentrations in normal brain, tumor rim, and tumor core were above in vitro effective radiosensitizing concentrations. These results indicate that despite being a substrate of efflux in the mouse brain, sufficient AZD1390 exposure is anticipated even in regions of normal brain. SIGNIFICANCE STATEMENT: Given the invasive nature of glioblastoma (GBM), tumor cells are often protected by an intact blood-brain barrier, requiring the development of brain-penetrant molecules for effective treatment. We show that efflux mediated by P-glycoprotein (P-gp) limits central nervous system (CNS) distribution of AZD1390 and that there are no distributional differences within anatomical regions of CNS. Despite efflux by P-gp, concentrations effective for potent radiosensitization are achieved in GBM tumor-bearing mouse brains, indicating that AZD1390 is an attractive molecule for clinical development of brain tumors.

P-glycoprotein: new insights into structure, physiological function, regulation and alterations in disease

The multidrug resistance phenomenon presents a major threat to the pharmaceutical industry. This resistance is a common occurrence in several diseases and is mediated by multidrug transporters that actively pump substances out of the cell and away from their target regions. The most well-known multidrug transporter is the P-glycoprotein transporter. The binding sites within P-glycoprotein can accommodate a variety of compounds with diverse structures. Hence, numerous drugs are P-glycoprotein substrates, with new ones being identified every day. For many years, the mechanisms of action of P-glycoprotein have been shrouded in mystery, and scientists have only recently been able to elucidate certain structural and functional aspects of this protein. Although P-glycoprotein is highly implicated in multidrug resistant diseases, this transporter also performs various physiological roles in the human body and is expressed in several tissues, including the brain, kidneys, liver, gastrointestinal tract, testis, and placenta. The expression levels of P-glycoprotein are regulated by different enzymes, inflammatory mediators and transcription factors; alterations in which can result in the generation of a disease phenotype. This review details the discovery, the recently proposed structure and the regulatory functions of P-glycoprotein, as well as the crucial role it plays in health and disease.

Role of the Efflux Transporters Abcb1 and Abcg2 in the Brain Distribution of Olaparib in Mice

Olaparib is a first-in-class poly (ADP-ribose) polymerase oral inhibitor used to treat various tumors. In this study, we clarified the roles of ABCB1/Abcb1 and ABCG2/Abcg2 transporters in restricting olaparib distribution to the brain. Olaparib was efficiently transported by human ABCG2, human ABCB1, and mouse Abcg2 in vitro. In the in vivo disposition study of olaparib using single or combination knockout mice, the systemic exposure of olaparib did not differ significantly between the strains over an 8-h period. However, the brain-to-plasma unbound concentration ratio of olaparib increased 5.6- and 8.1-fold in Abcb1a/1b and Abcb1a/1b;Abcg2 knockout mice, respectively, compared with wild-type mice. The Abcg2 single knockout mice exhibited a similar brain-to-plasma unbound concentration ratio to wild-type mice. Moreover, the brain distribution of olaparib could be modulated by the ABCB1/ABCG2 dual inhibitor elacridar to reach a similar degree of inhibition to Abcb1a/1b^-/-. These findings suggest that olaparib is actively transported by both human and mouse ABCB1/Abcb1 and ABCG2/Abcg2; while Abcb1a/1b is a major determinant of olaparib brain penetration in mice, Abcg2 is likely to be a minor contributor. Concomitant treatment with temozolomide slightly increased the brain distribution of olaparib in mouse, but the clinical impact of the interaction was expected to be limited.

Thromboembolic Risks with Concurrent Direct Oral Anticoagulants and Antiseizure Medications: A Population-Based Analysis

BACKGROUND AND OBJECTIVE

Drug-drug interactions between direct oral anticoagulants (DOAC) and antiseizure medications via the cytochrome P450 (CYP) or the P-glycoprotein (P-gp) systems may lead to under-anticoagulation. The clinical relevance of these interactions is unclear. We aimed to elucidate the risk of thromboembolism with concurrent DOAC and CYP/P-gp modulating antiseizure medications.

METHODS

In this propensity score-weighted population-based retrospective cohort study, we used competing risk regression analyses to determine the risks of ischemic stroke, venous thromboembolism, and death in DOAC recipients taking CYP/P-gp-modulating antiseizure medications (phenytoin, valproate, levetiracetam, carbamazepine, or phenobarbital) versus those taking CYP/P-gp-neutral antiseizure medications (pregabalin, gabapentin, or clobazam). We also performed secondary analyses for the epilepsy and atrial fibrillation subgroups.

RESULTS

Among DOAC users, CYP/P-gp-modulating antiseizure medications were collectively associated with an increased risk of ischemic stroke (adjusted hazard ratio 1.28, 95% confidence interval 1.05-1.57, p = 0.017). In addition, phenytoin (adjusted hazard ratio 1.34, 95% confidence interval 1.07-1.68, p = 0.011) and valproate (adjusted hazard ratio 1.38, 95% confidence interval 1.10-1.74, p = 0.006) were associated with increased mortality. In the epilepsy subgroup, the risk of ischemic stroke and venous thromboembolism did not differ between CYP/P-gp-modulating and CYP/P-gp-neutral antiseizure medications.

CONCLUSIONS

Although CYP/P-gp-modulating antiseizure medications were associated with an increased risk of ischemic stroke when paired with DOAC in the primary analysis, such a phenomenon was not found among patients with epilepsy who took phenytoin, valproate, or levetiracetam with DOAC. Therefore, these antiseizure medication options among patients with epilepsy with concurrent DOAC should not be restricted solely based on their potential drug-drug interactions. Yet, the increased mortality during concurrent use of DOAC with phenytoin or valproate might call for caution.

Comparative vulnerability of PET radioligands to partial inhibition of P-glycoprotein at the blood-brain barrier: A criterion of choice?

Only partial deficiency/inhibition of P-glycoprotein (P-gp, ABCB1) function at the blood-brain barrier (BBB) is likely to occur in pathophysiological situations or drug-drug interactions. This raises questions regarding the sensitivity of available PET imaging probes to detect moderate changes in P-gp function at the living BBB. In vitro, the half-maximum inhibitory concentration (IC₅₀) of the potent P-gp inhibitor tariquidar in P-gp-overexpressing cells was significantly different using either [¹¹C]verapamil (44 nM), [¹¹C]N-desmethyl-loperamide (19 nM) or [¹¹C]metoclopramide (4 nM) as substrate probes. In vivo PET imaging in rats showed that the half-maximum inhibition of P-gp-mediated efflux of [¹¹C]metoclopramide, achieved using 1 mg/kg tariquidar (in vivo IC₅₀ = 82 nM in plasma), increased brain exposure by 2.1-fold for [¹¹C]metoclopramide (p < 0.05, n = 4) and 2.4-fold for [¹¹C]verapamil (p < 0.05, n = 4), whereby cerebral uptake of the "avid" substrate [¹¹C]N-desmethyl-loperamide was unaffected (p > 0.05, n = 4). This comparative study points to differences in the "vulnerability" to P-gp inhibition among radiolabeled substrates, which were apparently unrelated to their "avidity" (maximal response to P-gp inhibition). Herein, we advocate that partial inhibition of transporter function, in addition to complete inhibition, should be a primary criterion of evaluation regarding the sensitivity of radiolabeled substrates to detect moderate but physiologically-relevant changes in transporter function in vivo.

Screening novel CNS drug candidates for P-glycoprotein interactions using the cell line iP-gp: In vitro efflux ratios from iP-gp and MDCK-MDR1 monolayers compared to brain distribution data from mice

Drug efflux by P-glycoprotein (P-gp, ABCB1) is considered as a major obstacle for brain drug delivery for small molecules. P-gp-expressing cell monolayers are used for screening of new drug candidates during early states of drug development. It is, however, uncertain how well the in vitro studies can predict the in vivo P-gp mediated efflux at the blood-brain barrier (BBB). We previously developed a novel cell line of porcine origin, the iP-gp cell line, with high transepithelial resistance and functional expression of human P-gp. The aim of the present study was to evaluate the applicability of the cell line for screening of P-gp interactions of novel drug candidates. For this purpose, bidirectional fluxes of 14 drug candidates were measured in iP-gp cells and in MDCK-MDR1 cells, and compared with pharmacokinetic data obtained in male C57BL/6 mice. The iP-gp cells formed extremely tight monolayers (>15 000 Ω∙cm²) as compared to the MDCK- MDR1 cells (>250 Ω∙cm²) and displayed lower P_app,a-b values. The efflux ratios obtained with iP-gp and MDCK-MDR1 monolayers correlated with K_p,uu,brain values from the in vivo studies, where compounds with the lowest K_p,uu,brain generally displayed the highest efflux ratios. 12 of the tested compounds displayed a poor BBB penetration in mice as judged by K_p,uu less than 1. Of these compounds, nine compounds were categorized as P-gp substrates in the iP-gp screening, whereas analysis of data estimated in MDCK-MDR1 cells indicated four compounds as potential substrates. The results suggest that the iP-gp cell model may be a sensitive and useful screening tool for drug screening purposes to identify possible substrates of human P-glycoprotein.

The road (not) taken - Placental transfer and interspecies differences

Species differences are among the main reasons for the high failure rate of preclinical studies. A better awareness and understanding of these differences might help to improve the outcome of preclinical research. In reproduction, the placenta is the central organ regulating fetal exposure to a substance circulating in the maternal organism. Exact information about placental transfer can help to better estimate the toxic potential of a substance. From an evolutionary point of view, the chorioallantoic placenta is the organ with the highest anatomical diversity among species. Moreover, frequently used animal models in reproduction belong to rodents and lagomorphs, two groups that are characterized by the generation of an additional type of placenta, which is crucial for fetal development, but absent from humans: the inverted yolk sac placenta. Taken together, the translatability of placental transfer studies from laboratory animals to humans is challenging, which is supported by the fact that numerous species-dependent toxic effects are described in literature. Thus, reliable human-relevant data are frequently lacking and the toxic potential of chemicals and pharmaceuticals for humans can hardly be estimated, often resulting in recommendations that medical treatments or exposure to chemicals should be avoided for safety reasons. Although species differences of placental anatomy have been described frequently and the need for human-relevant research models has been emphasized, analyses of substances with species-dependent placental transfer have been performed only sporadically. Here, we present examples for species-specific placental transfer, including that of nanoparticles and pharmaceuticals, and discuss potential underlying mechanisms. With respect to the COVID 19-pandemic it might be of interest that some antiviral drugs are reported to feature species-specific placental transfer. Further, differences in placental structure and antibody transfer may affect placental transfer of ZIKA virus.

Chaihu plus Longgu Muli Decoction Alleviated Brain Injury in Pentylenetetrazole-Kindled Epileptic Mice by Regulating Cyclooxygenase-2/Prostaglandin E2/Multidrug Transporter Pathway

Objective. To evaluate the effect of CLMD administration on epileptic seizures and brain injury in pentylenetetrazole- (PZT-) kindled mice. Methods. The effect of pretreatment with CLMD (5, 10, and 20 ml/kg (mg/kg) by gavage) for seven days on PTZ-induced kindling, duration and grade of kindling-induced seizures, and pathological injury in the cortex and hippocampus was evaluated. Male BALB/c mice with adenosine A1 receptor knockout were subjected to intraperitoneal injection of PTZ (35 mg/kg) once every day until kindling was successfully induced. Quantitative reverse transcription polymerase chain reaction, immunofluorescence, and western blot were performed to assess the mRNA and protein levels of p-glycoprotein (PGP), multidrug resistance-associated protein 1 (MRP1), cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2), and adenylate kinase (ADK) in the cortex and hippocampus. Results. PTZ successfully induced kindling in mice after 21 days, wherein CLMD showed an obvious dose-dependent antiepileptic effect. High-dose CLMD significantly increased the latency of epileptic seizures, decreased the sustained time of epileptic seizures and the seizure grade, and ameliorated the histopathological changes in the cortex and hippocampus. Furthermore, PTZ kindling induced significantly higher levels of PGP, MRP1, COX-2, PGE2, and ADK, but this effect was inhibited by pretreatment with CLMD in a dose-dependent manner. Conclusion. Pretreatment with CLMD attenuates PTZ-kindled convulsions and brain injury in mice. The mechanism may be related to the cyclooxygenase-2/prostaglandin E2/multidrug transporter pathway.

Non-vitamin K Oral Anticoagulants and Anti-seizure Medications: A Retrospective Cohort Study

Purpose: Concerns of drug-drug interactions (DDIs) between anti-seizure medications (ASMs) and non-vitamin K oral anticoagulants (NOACs) have emerged in recent case reports and guidelines. Theoretically, the induction of hepatic cytochrome P450 3A4 (CYP3A4) enzyme and permeability glycoprotein (P-GP) efflux transporter protein systems may reduce the effect of NOACs. We aimed to investigate whether such DDIs are clinically relevant in a real-world situation. Methods: We retrospectively reviewed 320 ischemic stroke patients with atrial fibrillation (Af) and grouped them according to different potential interactions with CYP3A4 and P-GP. Ischemic stroke events, transient ischemic attack (TIA) events, follow-up duration, baseline characteristics, concomitant ASMs, and stroke risk factors were collected. Statistical analysis included Kaplan-Meier survival curves and the log-rank test. Results: Overall, 320 ischemic stroke with Af patients received NOACs. Among the NOAC users, 75 also took ASMs, including 56 that have potential DDIs: 43 (13.4%) were categorized as potential CYP and P-GP DDIs and 13 (4.1%) as P-GP-only DDIs. The remaining 264 (82.5%) patients were used as controls including 19 exposed to nonsignificant DDI ASMs and 245 patients without ASM exposure. The incidence rates of recurrent stroke/TIA events in both CYP3A4 and P-GP DDIs, P-GP DDIs only, and no DDIs were 7.5, 2.1, and 8.4/100 person-years, respectively. Kaplan-Meier survival curves and the log-rank test did not show significant differences among the groups. Conclusions: The recurrent stroke rate of NOAC users with potential DDIs was not higher than in those without potential DDIs in this single-institute study. Our results suggest that theoretical interactions between ASMs and NOACs may not be as severe as previously thought in a real-world situation.

Impact of CNS Diseases on Drug Delivery to Brain Extracellular and Intracellular Target Sites in Human: A "WHAT-IF" Simulation Study

The blood-brain barrier (BBB) is equipped with unique physical and functional processes that control central nervous system (CNS) drug transport and the resulting concentration-time profiles (PK). In CNS diseases, the altered BBB and CNS pathophysiology may affect the CNS PK at the drug target sites in the brain extracellular fluid (brainECF) and intracellular fluid (brainICF) that may result in changes in CNS drug effects. Here, we used our human CNS physiologically-based PK model (LeiCNS-PK3.0) to investigate the impact of altered cerebral blood flow (CBF), tight junction paracellular pore radius (pararadius), brainECF volume, and pH of brainECF (pHECF) and of brainICF (pHICF) on brainECF and brainICF PK for 46 small drugs with distinct physicochemical properties. LeiCNS-PK3.0 simulations showed a drug-dependent effect of the pathophysiological changes on the rate and extent of BBB transport and on brainECF and brainICF PK. Altered pararadius, pHECF, and pHICF affected both the rate and extent of BBB drug transport, whereas changes in CBF and brainECF volume modestly affected the rate of BBB drug transport. While the focus is often on BBB paracellular and active transport processes, this study indicates that also changes in pH should be considered for their important implications on brainECF and brainICF target site PK.

Possible interplay between the theories of pharmacoresistant epilepsy

Epilepsy is one of the oldest known neurological disorders and is characterized by recurrent seizure activity. It has a high incidence rate, affecting a broad demographic in both developed and developing countries. Comorbid conditions are frequent in patients with epilepsy and have detrimental effects on their quality of life. Current management options for epilepsy include the use of anti-epileptic drugs, surgery, or a ketogenic diet. However, more than 30% of patients diagnosed with epilepsy exhibit drug resistance to anti-epileptic drugs. Further, surgery and ketogenic diets do little to alleviate the symptoms of patients with pharmacoresistant epilepsy. Thus, there is an urgent need to understand the underlying mechanisms of pharmacoresistant epilepsy to design newer and more effective anti-epileptic drugs. Several theories of pharmacoresistant epilepsy have been suggested over the years, the most common being the gene variant hypothesis, network hypothesis, multidrug transporter hypothesis, and target hypothesis. In our review, we discuss the main theories of pharmacoresistant epilepsy and highlight a possible interconnection between their mechanisms that could lead to the development of novel therapies for pharmacoresistant epilepsy.

Equine Drug Transporters: A Mini-Review and Veterinary Perspective

Xenobiotic transport proteins play an important role in determining drug disposition and pharmacokinetics. Our understanding of the role of these important proteins in humans and pre-clinical animal species has increased substantially over the past few decades, and has had an important impact on human medicine; however, veterinary medicine has not benefitted from the same quantity of research into drug transporters in species of veterinary interest. Differences in transporter expression cause difficulties in extrapolation of drug pharmacokinetic parameters between species, and lack of knowledge of species-specific transporter distribution and function can lead to drug–drug interactions and adverse effects. Horses are one species in which little is known about drug transport and transporter protein expression. The purpose of this mini-review is to stimulate interest in equine drug transport proteins and comparative transporter physiology.

Rapidly (and Successfully) Translating Novel Brain Radiotracers From Animal Research Into Clinical Use

The advent of preclinical research scanners for in vivo imaging of small animals has added confidence into the multi-step decision-making process of radiotracer discovery and development. Furthermore, it has expanded the utility of imaging techniques available to dissect clinical questions, fostering a cyclic interaction between the clinical and the preclinical worlds. Significant efforts from medicinal chemistry have also made available several high-affinity and selective compounds amenable for radiolabeling, that target different receptors, transporters and enzymes in vivo. This substantially increased the range of applications of molecular imaging using positron emission tomography (PET) or single photon emission computed tomography (SPECT). However, the process of developing novel radiotracers for in vivo imaging of the human brain is a multi-step process that has several inherent pitfalls and technical difficulties, which often hampers the successful translation of novel imaging agents from preclinical research into clinical use. In this paper, the process of radiotracer development and its relevance in brain research is discussed; as well as, its pitfalls, technical challenges and future promises. Examples of successful and unsuccessful translation of brain radiotracers will be presented.

A face-to-face comparison of claudin-5 transduced human brain endothelial (hCMEC/D3) cells with porcine brain endothelial cells as blood-brain barrier models for drug transport studies

BACKGROUND

Predictive in vitro models of the human blood-brain barrier (BBB) are essential in early drug discovery and development. Among available immortalized human brain capillary endothelial cell lines (BCECs), the hCMEC/D3 cell line has become the most widely used in vitro BBB model. However, monolayers of hCMEC/D3 cells form only moderately restrictive barriers, most likely because the major tight junction protein, claudin-5, is markedly downregulated. Thus, hCMEC/D3 monolayers cannot be used for vectorial drug transport experiments, which is a major disadvantage of this model.

METHODS

Here we transduced hCMEC/D3 cells with a claudin-5 plasmid and compared the characteristics of these cells with those of hCMEC/D3 wildtype cells and primary cultured porcine BCECs.

RESULTS

The claudin-5 transduced hCMEC/D3 exhibited expression levels (and junctional localization) of claudin-5 similar to those of primary cultured porcine BCECs. The transduced cells exhibited increased TEER values (211 Ω cm²) and reduced paracellular mannitol permeability (8.06%/h), indicating improved BBB properties; however, the barrier properties of porcine BCECs (TEER 1650 Ω cm²; mannitol permeability 3.95%/h) were not reached. Hence, vectorial transport of a selective P-glycoprotein substrate (N-desmethyl-loperamide) was not observed in claudin-5 transduced hCMEC/D3 (or wildtype) cells, whereas such drug transport occurred in porcine BCECs.

CONCLUSIONS

The claudin-5 transduced hCMEC/D3 cells provide a tool to studying the contribution of claudin-5 to barrier tightness and how this can be further enhanced by additional transfections or other manipulations of this widely used in vitro model of the BBB.

IPEC-J2 rMdr1a, a New Cell Line with Functional Expression of Rat P-glycoprotein Encoded by Rat Mdr1a for Drug Screening Purposes

The efflux pump P-glycoprotein (P-gp) affects drug distribution after absorption in humans and animals. P-gp is encoded by the multidrug resistance gene (MDR1) gene in humans, while rodents (the most common preclinical animal model) express the two isoforms Mdr1a and Mdr1b. Differences in substrate selectivity has also been reported. Our aim was to generate an in vitro cell model with tight barrier properties, expressing functional rat Mdr1a P-gp, as an in vitro tool for investigating species differences. The IPEC-J2 cell line forms extremely tight monolayers and was transfected with a plasmid carrying the rat Mdr1a gene sequence. Expression and P-gp localization at the apical membrane was demonstrated with Western blots and immunocytochemistry. Function of P-gp was shown through digoxin transport experiments in the presence and absence of the P-gp inhibitor zosuquidar. Bidirectional transport experiments across monolayers of the IPEC-J2 rMDR1a cell line and the IPEC-J2 MDR1 cell line, expressing human P-gp, showed comparable magnitude of transport in both the absorptive and efflux direction. We conclude that the newly established IPEC-J2 rMdr1a cell line, in combination with our previously established cell line IPEC-J2 MDR1, has the potential to be a strong in vitro tool to compare P-gp substrate profiles of rat and human P-gp.

The effect of cannabidiol on the pharmacokinetics of carbamazepine in rats

Carbamazepine (CBZ) is mainly metabolized by CYP3A4 into carbamazepine-10,11-epoxide (CBZE). Cannabidiol (CBD) is a potent inhibitor of the CYP3A family. The aim of this study is to determine the effect of acute and chronic administration of CBD on the pharmacokinetics of CBZ and CBZE. Male SD rats were assigned into four acute and four chronic groups: control (CBZ only), positive control (ketoconazole), low-dose cannabidiol (l-CBD), and high-dose cannabidiol (h-CBD). Acute CBD groups were administered a single dose of CBD, while chronic CBD groups were given multiple doses of CBD for 14 days (q.d.) before CBZ administration. Plasma samples had been collected and analyzed for CBZ and CBZE, then their noncompartmental pharmacokinetic parameters before and after CBD administration were determined. The co-administration of a single l-CBD has significantly increased CBZ's [Formula: see text] by 53.1%. Furthermore, CBZE kinetics showed a significant decrease in C_max by 31.8%. Acute h-CBD caused similar effects on CBZ's [Formula: see text] with 40.4% significant decrease in CBZE's C_max, when compared to the control. Chronic h-CBD caused a significant decrease in CBZ's C_max and [Formula: see text] by 75.3% and 65.7%, respectively. Besides, [Formula: see text] and C_max of CBZE significantly decreased by 75.3% and 78.3%, respectively. These results demonstrated that the pharmacokinetics of CBZ and CBZE had been significantly affected by CBD. When CBD has been administered as a single dose, the effect is believed to be mainly caused by the inhibition of CBZ metabolism through CYP3A. The effect of chronic administration of CBD probably includes kinetic pathways other than the inhibition of CYP3A-dependent pathways. Graphical abstract.

Activation of adenosine receptors modulates the efflux transporters in brain capillaries and restores the anticonvulsant effect of carbamazepine in carbamazepine resistant rats developed by window-pentylenetetrazole kindling

Up-regulation of efflux transporters in brain capillaries may lead to the decreased therapeutic efficacy of antiepileptic drugs in patients with Drug Resistant Epilepsy. Adenosine receptor activation in brain capillaries can modulate blood-brain barrier permeability by decreasing the protein levels and function of efflux transporters. Therefore, we aimed to investigate whether the activation of adenosine receptors improves convulsions outcome in carbamazepine (CBZ) resistant animals and modulates the protein levels of efflux transporters (P-GP, MRP1, MRP2) in brain capillaries. We employed the window-pentylenetetrazol (PTZ) kindling model to develop CBZ resistant rats by CBZ administration during the post-kindling phase, and tested if these animals displayed subsequent resistance to other antiepileptic drugs. Crucially, we investigated if the administration of a broad-spectrum adenosine agonist (NECA) improves convulsions control in CBZ resistant rats. Of potential therapeutic relevance, in CBZ resistant rats NECA restored the anticonvulsant effect of CBZ. We also evaluated how the resistance to CBZ and the activation of adenosine receptors with NECA affect protein levels of efflux transporters in brain capillaries, as quantified by western blot. While CBZ resistance was associated with the up-regulation of both P-GP/MRP2 in brain capillaries, with the administration of NECA in CBZ resistant rats, we observed a decrease of P-GP and an increase of MRP2 levels, in brain capillaries. Since the activation of adenosine receptors improves the outcome of convulsions probably through the modulation of the efflux transporters protein levels in brain capillaries, adenosine agonists could be useful as an adjunct therapy for the control of Drug Resistant Epilepsy.

Assessing major bleeding risk in atrial fibrillation patients concurrently taking non-vitamin K antagonist oral anticoagulants and antiepileptic drugs

Aims

This study compared the risk of major bleeding between atrial fibrillation (AF) patients who took non-vitamin K antagonist oral anticoagulants (NOACs) and antiepileptic drugs (AEDs) concurrently and those who took only NOACs.

Methods and results

We performed a retrospective cohort study using Taiwan National Health Insurance database and included AF patients who received NOAC prescriptions from 1 June 2012 to 31 December 2017. The major bleeding risks of person-quarters exposed to NOAC and 11 concurrent AEDs (carbamazepine, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, phenobarbital, phenytoin, pregabalin, topiramate, valproic acid, and zonisamide) were compared with person-quarters exposed to NOAC alone. Adjusted incidence rate differences between NOAC with or without concurrent AEDs were estimated using Poisson regression models weighted by the inverse probability of treatment. Among 104 319 patients (age 75.0 ± 10.3 years; men, 56.2%), 8546 major bleeding events occurred during 731 723 person-quarters with NOAC prescriptions. Concurrent AED use was found in 15.3% of NOAC-treated patients. Concurrent use of NOAC with valproic acid, phenytoin, or levetiracetam increased adjusted incidence rates per 1000 person-years of major bleeding more significantly than NOAC alone: 153.49 for NOAC plus valproic acid vs. 55.06 for NOAC alone [difference 98.43, 95% confidence interval (CI) 82.37–114.49]; 135.83 for NOAC plus phenytoin vs. 54.43 for NOAC alone (difference 81.4, 95% CI 60.14–102.66); and 132.96 for NOAC plus levetiracetam vs. 53.08 for NOAC alone (difference 79.88, 95% CI 64.47–95.30).

Conclusion

For AF patients, the concurrent use of NOACs and valproic acid, phenytoin, or levetiracetam was associated with a higher risk of major bleeding.

ABC transporters in drug-resistant epilepsy: mechanisms of upregulation and therapeutic approaches

Drug-resistant epilepsy (DRE) affects approximately one third of epileptic patients. Among various theories that try to explain multidrug resistance, the transporter hypothesis is the most extensively studied. Accordingly, the overexpression of efflux transporters in the blood-brain barrier (BBB), mainly from the ATP binding cassette (ABC) superfamily, may be responsible for hampering the access of antiepileptic drugs into the brain. P-glycoprotein and other efflux transporters are known to be upregulated in endothelial cells, astrocytes and neurons of the neurovascular unit, a functional barrier critically involved in the brain penetration of drugs. Inflammation and oxidative stress involved in the pathophysiology of epilepsy together with uncontrolled recurrent seizures, drug-associated induction and genetic polymorphisms are among the possible causes of ABC transporters overexpression in DRE. The aforementioned pathological mechanisms will be herein discussed together with the multiple strategies to overcome the activity of efflux transporters in the BBB - from direct transporters inhibition to down-regulation of gene expression resorting to RNA interference (RNAi), or by targeting key modulators of inflammation and seizure-mediated signalling.

Humanization of the Blood-Brain Barrier Transporter ABCB1 in Mice Disrupts Genomic Locus - Lessons from Three Unsuccessful Approaches

ATP-binding cassette (ABC) transporters are of major importance for the restricted access of toxins and drugs to the human body. At the body's barrier tissues like the blood-brain barrier, these transporters are highly represented. Especially, ABCB1 (P-glycoprotein) has been a priority target of pharmaceutical research, for instance, to aid chemotherapy of cancers, therapy resistant epilepsy, and lately even neurodegenerative diseases. To improve translational research, the humanization of mouse genes has become a popular tool although, like recently seen for Abcb1, not all approaches were successful. Here, we report the characterization of another unsuccessful commercially available ABCB1 humanized mouse strain. In vivo assessment of transporter activity using positron emission tomography imaging revealed a severe reduction of ABCB1 function in the brain of these mice. Analyses of brain mRNA and protein expression showed that the murine Abcb1a gene is still expressed in homozygous humanized animals while expression of the human gene is minimal. Promoter region analyses underpinned that the introduced human gene might dysregulate normal expression and provided insights into the regulation of both transcription and translation of Abcb1a. We conclude that insertion of the human coding DNA sequence (CDS) into exon 3 instead of exon 2 most probably represents a more promising strategy for Abcb1a humanization.

Interspecies comparison of putative ligand binding sites of human, rat and mouse P-glycoprotein

Prior to the clinical phases of testing, safety, efficacy and pharmacokinetic profiles of lead compounds are evaluated in animal studies. These tests are primarily performed in rodents, such as mouse and rats. In order to reduce the number of animal experiments, computational models that predict the outcome of these studies and thus aid in prioritization of preclinical candidates are heavily needed. However, although computational models for human off-target interactions with decent quality are available, they cannot easily be transferred to rodents due to lack of respective data. In this study, we assess the transferability of human P-glycoprotein activity data for development of in silico models to predict in vivo effects in rats and mouse using a structure-based approach. P-glycoprotein (P-gp) is an ATP-dependent efflux transporter that transports xenobiotic compounds such as toxins and drugs out of cells and has a broad substrate and inhibitor specificity. Being mostly expressed at barriers, it influences the bioavailability of drugs and thus contributes also to toxicity. Comparison of the binding site interaction profiles of human, rat and mouse P-gp derived from docking studies with a set of common inhibitors suggests that the inhibitors share potentially similar binding modes. These findings encourage the use of in vitro human P-gp data for predicting in vivo effects in rodents and thus contributes to the 3Rs (Replace, Reduce and Refine) of animal experiments.

Phenytoin Could Potentially Increase Hepatic Clearance of 99mTc-Sestamibi in Myocardial Perfusion Imaging

Myocardial perfusion imaging (MPI) is one of the most commonly used nuclear medicine imaging modalities for coronary artery disease evaluation and risk stratification. The authors present incidental image findings in a patient who underwent MPI twice because of development of seizures just before the first SPECT-MPI acquisition. The projection images for first MPI done without medication (phenytoin) showed the retention of hepatic tracer activity. After a few days from restarting of phenytoin, the repeat MPI showed complete hepatic clearance of tracer. This case highlights the possible pharmacokinetic interaction between phenytoin intake and Tc-sestamibi, resulting in faster hepatic clearance of the radiotracer.

Characterization of P-Glycoprotein Humanized Mice Generated by Chromosome Engineering Technology: Its Utility for Prediction of Drug Distribution to the Brain in Humans

P-glycoprotein (P-gp), encoded by the MDR1 gene in humans and by the Mdr1a/1b genes in rodents, is expressed in numerous tissues and performs as an efflux pump to limit the distribution and absorption of many drugs. Owing to species differences of P-gp between humans and rodents, it is difficult to predict the impact of P-gp on pharmacokinetics and the tissue distribution of P-gp substrates in humans from the results of animal experiments. Therefore, we generated a novel P-gp humanized mouse model by using a mouse artificial chromosome (MAC) vector [designated human MDR1-MAC (hMDR1-MAC) mice]. The results showed that hMDR1 mRNA was expressed in various tissues of hMDR1-MAC mice. Furthermore, the expression of human P-gp was detected in the brain capillary fraction and plasma membrane fraction of intestinal epithelial cells isolated from hMDR1-MAC mice, although the expression levels of intestinal P-gp were extremely low. Thus, we evaluated the function of human P-gp at the blood-brain barrier of hMDR1-MAC mice. The brain-to-plasma ratios of P-gp substrates in hMDR1-MAC mice were much lower than those in Mdr1a/1b-knockout mice, and the brain-to-plasma ratio of paclitaxel was significantly increased by pretreatment with a P-gp inhibitor in hMDR1-MAC mice. These results indicated that the hMDR1-MAC mice are the first P-gp humanized mice expressing functional human P-gp at the blood-brain barrier. This mouse is a promising model with which to evaluate species differences of P-gp between humans and mice in vivo and to estimate the brain distribution of drugs in humans while taking into account species differences of P-gp.

Nanoparticle-based delivery of carbamazepine: A promising approach for the treatment of refractory epilepsy

Resistance to antiepileptic drugs (AEDs) is a major clinical problem. The overexpression of P-glycoprotein (Pgp), one of the main transporters limiting the entry of xenobiotics into the brain, is among the factors contributing to the AED resistance. Presently, there is no consensus on the interaction of carbamazepine (CBZ) with the Pgp. This study investigates the effect of the Pgp inhibitor verapamil on the anticonvulsant effect of CBZ and its nanoparticulate formulation in the rat model of isoniazid-induced epilepsy. Verapamil significantly increased the anticonvulsant effect of CBZ and reduced its effective dose by at least 30% (from 30 mg/kg to 20 mg/kg). Binding of carbamazepine to the poloxamer 188-coated PLGA nanoparticles enabled a 30-fold increase of its anticonvulsive effect, as compared to the free drug. The inhibition of Pgp did not influence the effectivity of carbamazepine encapsulated in nanoparticles.

Imaging techniques to study drug transporter function in vivo

Transporter systems involved in the permeation of drugs and solutes across biological membranes are recognized as key determinants of pharmacokinetics. Typically, the action of membrane transporters on drug exposure to tissues in living organisms is inferred from invasive procedures, which cannot be applied in humans. In recent years, imaging methods have greatly progressed in terms of instruments, synthesis of novel imaging probes as well as tools for data analysis. Imaging allows pharmacokinetic parameters in different tissues and organs to be obtained in a non-invasive or minimally invasive way. The aim of this overview is to summarize the current status in the field of molecular imaging of drug transporters. The overview is focused on human studies, both for the characterization of transport systems for imaging agents as well as for the determination of drug pharmacokinetics, and makes reference to animal studies where necessary. We conclude that despite certain methodological limitations, imaging has a great potential to study transporters at work in humans and that imaging will become an important tool, not only in drug development but also in medicine. Imaging allows the mechanistic aspects of transport proteins to be studied, as well as elucidating the influence of genetic background, pathophysiological states and drug-drug interactions on the function of transporters involved in the disposition of drugs.

Population Pharmacokinetic Modeling of Levetiracetam in Pediatric and Adult Patients With Epilepsy by Using Routinely Monitored Data

BACKGROUND

Levetiracetam, a second-generation antiepileptic drug, is frequently used for managing partial-onset seizures. About 70% of the administered dose is excreted in urine unchanged, and dosage adjustment is recommended based on the individual's renal function. In this study, a population pharmacokinetic model of levetiracetam was developed using routinely monitored serum concentration data for individualized levetiracetam therapy.

METHODS

Patients whose serum concentrations of levetiracetam at steady-state were routinely monitored at Kyoto University Hospital from April 2012 to March 2013 were enrolled. The influence of patient characteristics on levetiracetam pharmacokinetics was evaluated using the nonlinear mixed-effects modeling (NONMEM) program.

RESULTS

A total of 583 steady-state concentrations from 225 patients were used for the analysis. The median patient age and estimated glomerular filtration rate (eGFR) were 38 (range: 1-89) years and 98 (15-189) mL·min·1.73 m, respectively. Serum concentration-time data of levetiracetam were well described by a 1-compartment model with first-order absorption. Oral clearance was allometrically related to the individual body weight and eGFR. An increase in the dose significantly increased oral clearance. No improvement in model fit was observed by including the covariate of any concomitant antiepileptic drugs. The population mean clearance for an adult weighing 70 kg and with a normal renal function was 4.8 and 5.9 L/h for 500 mg bis in die (bid) and 1500 mg bid, respectively.

CONCLUSIONS

Oral clearance allometrically related with body weight and eGFR can well predict the routine therapeutic drug monitoring data from pediatric to aged patients with varying renal function. Dosage adjustments based on renal function are effective in controlling the trough and peak concentrations in similar ranges.

Renal Drug Transporters and Drug Interactions

Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.

Drug-Resistant Epilepsy: Multiple Hypotheses, Few Answers

Epilepsy is a common neurological disorder that affects over 70 million people worldwide. Despite the recent introduction of new antiseizure drugs (ASDs), about one-third of patients with epilepsy have seizures refractory to pharmacotherapy. Early identification of patients who will become refractory to ASDs could help direct such patients to appropriate non-pharmacological treatment, but the complexity in the temporal patterns of epilepsy could make such identification difficult. The target hypothesis and transporter hypothesis are the most cited theories trying to explain refractory epilepsy, but neither theory alone fully explains the neurobiological basis of pharmacoresistance. This review summarizes evidence for and against several major theories, including the pharmacokinetic hypothesis, neural network hypothesis, intrinsic severity hypothesis, gene variant hypothesis, target hypothesis, and transporter hypothesis. The discussion is mainly focused on the transporter hypothesis, where clinical and experimental data are discussed on multidrug transporter overexpression, substrate profiles of ASDs, mechanism of transporter upregulation, polymorphisms of transporters, and the use of transporter inhibitors. Finally, future perspectives are presented for the improvement of current hypotheses and the development of treatment strategies as guided by the current understanding of refractory epilepsy.

In vitro antineoplastic effects of brivaracetam and lacosamide on human glioma cells

Background

Epilepsy is a frequent symptom in patients with glioma. Although treatment with antiepileptic drugs is generally effective in controlling seizures, drug-resistant patients are not uncommon. Multidrug resistance proteins (MRPs) and P-gp are over-represented in brain tissue of patients with drug-resistant epilepsy, suggesting their involvement in the clearance of antiepileptic medications. In addition to their anticonvulsant action, some drugs have been documented for cytotoxic effects. Aim of this study was to evaluate possible in vitro cytotoxic effects of two new-generation antiepileptic drugs on a human glioma cell line U87MG.

Methods

Cytotoxicity of brivaracetam and lacosamide was tested on U87MG, SW1783 and T98G by MTS assay. Expression of chemoresistance molecules was evaluated using flow cytometry in U87MG and human umbilical vein endothelial cells (HUVECs). To investigate the putative anti-proliferative effect, apoptosis assay, microRNA expression profile and study of cell cycle were performed.

Results

Brivaracetam and lacosamide showed a dose-dependent cytotoxic and anti-migratory effects. Cytotoxicity was not related to apoptosis. The exposure of glioma cells to brivaracetam and lacosamide resulted in the modulation of several microRNAs; particularly, the effect of miR-195-5p modulation seemed to affect cell cycle, while miR-107 seemed to be implicated in the inhibition of cells migration. Moreover, brivaracetam and lacosamide treatment did not modulate the expression of chemoresistance-related molecules MRPs1-3-5, GSTπ, P-gp on U87MG and HUVECs.

Conclusion

Based on antineoplastic effect of brivaracetam and lacosamide on glioma cells, we assume that patients with glioma could benefit by the treatment with these two molecules, in addition to standard therapeutic options.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-017-0546-9) contains supplementary material, which is available to authorized users.

Inhibition of mTOR Pathway by Rapamycin Decreases P-glycoprotein Expression and Spontaneous Seizures in Pharmacoresistant Epilepsy

The mammalian target of rapamycin (mTOR) has been demonstrated to mediate multidrug resistance in various tumors by inducing P-glycoprotein (P-gp) overexpression. Here, we investigated the correlation between the mTOR pathway and P-gp expression in pharmacoresistant epilepsy. Temporal cortex specimens were obtained from patients with refractory mesial temporal lobe epilepsy (mTLE) and age-matched controls who underwent surgeries at West China Hospital of Sichuan University between June 2014 and May 2015. We established a rat model of epilepsy kindled by coriaria lactone (CL) and screened pharmacoresistant rats (non-responders) using phenytoin. Non-responders were treated for 4 weeks with vehicle only or with the mTOR pathway inhibitor rapamycin at doses of 1, 3, and 6 mg/kg. Western blotting and immunohistochemistry were used to detect the expression of phospho-S6 (P-S6) and P-gp at different time points (1 h, 8 h, 1 day, 3 days, 1 weeks, 2 weeks, and 4 weeks) after the onset of treatment. Overexpression of P-S6 and P-gp was detected in both refractory mTLE patients and non-responder rats. Rapamycin showed an inhibitory effect on P-S6 and P-gp expression 1 week after treatment in rats. In addition, the expression levels of P-S6 and P-gp in the 6 mg/kg group were significantly lower than those in the 1 mg/kg or the 3 mg/kg group at the same time points (all P < 0.05). Moreover, rapamycin decreased the duration and number of CL-induced seizures, as well as the stage of non-responders (all P < 0.05). The current study indicates that the mTOR signaling pathway plays a critical role in P-gp expression in drug-resistant epilepsy. Inhibition of the mTOR pathway by rapamycin may be a potential therapeutic approach for pharmacoresistant epilepsy.

Cardiovascular Ion Channel Inhibitor Drug-Drug Interactions with P-glycoprotein

P-glycoprotein (Pgp) is an ATP-binding cassette (ABC) transporter that plays a major role in cardiovascular drug disposition by effluxing a chemically and structurally diverse range of cardiovascular therapeutics. Unfortunately, drug-drug interactions (DDIs) with the transporter have become a major roadblock to effective cardiovascular drug administration because they can cause adverse drug reactions (ADRs) or reduce the efficacy of drugs. Cardiovascular ion channel inhibitors are particularly susceptible to DDIs and ADRs with Pgp because they often have low therapeutic indexes and are commonly coadministered with other drugs that are also Pgp substrates. DDIs from cardiovascular ion channel inhibitors with the transporter occur because of inhibition or induction of the transporter and the transporter's tissue and cellular localization. Inhibiting Pgp can increase absorption and reduce excretion of drugs, leading to elevated drug plasma concentrations and drug toxicity. In contrast, inducing Pgp can have the opposite effect by reducing the drug plasma concentration and its efficacy. A number of in vitro and in vivo studies have already demonstrated DDIs from several cardiovascular ion channel inhibitors with human Pgp and its animal analogs, including verapamil, digoxin, and amiodarone. In this review, Pgp-mediated DDIs and their effects on pharmacokinetics for different categories of cardiovascular ion channel inhibitors are discussed. This information is essential for improving pharmacokinetic predictions of cardiovascular therapeutics, for safer cardiovascular drug administration and for mitigating ADRs emanating from Pgp.

Factors influencing the fabrication of albumin-bound drug nanoparticles (ABDns): Part II. Albumin-bound carbamazepine nanoparticles (ABCns)

Carbamazepine (CBZ) is a BCS Class II drug with poor solubility profile. In order to improve the physicochemical properties of CBZ, albumin (HSA)-bound CBZ nanoparticles (ABCns) were prepared. Drug-loading studies indicated that monomeric ABCns can be fabricated by self-assembly of anhydrous form III of CBZ and HSA in molar ratios of 1:1 or 2:1 within 0.5 h in phosphate buffer pH 7.4 with particle size in the range of 10-20 nm. Approximately 73-76% of the CBZ was encapsulated within HSA and 20-40% CBZ was released from the ABCns over 8 days. In conclusion, novel ABCns can be fabricated with sustained-release of CBZ for over 8 days which can significantly improve the physicochemical profile of CBZ.

Role of Human Breast Cancer Related Protein versus P-Glycoprotein as an Efflux Transporter for Benzylpenicillin: Potential Importance at the Blood-Brain Barrier

While the blood-brain barrier (BBB) protects the brain by controlling the access of solutes and toxic substances to brain, it also limits drug entry to treat central nervous system disorders. Many drugs are substrates for ATP-binding cassette (ABC) transporters at the BBB that limit their entry into the brain. The role of those transporters in limiting the entry of the widely prescribed therapeutic, benzylpenicillin, has produced conflicting results. This study investigated the possible potential involvement of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), two ABC transporters, in benzylpenicillin transport at BBB in human using MDCKII cells overexpressing those transporters as well as pharmacological inhibition. MDCKII cells overexpressing human BCRP (MDCKII-BCRP) but not those overexpressing human P-gp (MDCKII-MDR cells) had reduced [3H]benzylpenicillin uptake. Similarly, inhibiting BCRP increased [3H]benzylpenicillin uptake in MDCKII-BCRP cells, while inhibiting P-gp in MDCKII-MDR cells had no effect on uptake although there was evidence that benzylpenicillin is a substrate for canine P-gp. While inhibiting BCRP affected [3H]benzylpenicillin cell concentrations it did not affect transepithelial flux in MDCKII-BCRP cells. In summary, the results indicate that human BCRP and not human P-gp is involved in benzylpenicillin transport. However, targeting BCRP alone was not sufficient to alter transepithelial flux in MDCKII cells. Whether it would be sufficient to alter blood-to-brain flux at the human BBB remains to be investigated.

Knockout of P-glycoprotein does not alter antiepileptic drug efficacy in the intrahippocampal kainate model of mesial temporal lobe epilepsy in mice

Pharmacoresistance to antiepileptic drugs (AEDs) is a major challenge in epilepsy therapy, affecting at least 30% of patients. Thus, there is considerable interest in the mechanisms responsible for such pharmacoresistance, with particular attention on the specific cellular and molecular factors that lead to reduced drug sensitivity. Current hypotheses of refractory epilepsy include the multidrug transporter hypothesis, which posits that increased expression or function of drug efflux transporters, such as P-glycoprotein (Pgp), in brain capillaries reduces the local concentration of AEDs in epileptic brain regions to subtherapeutic levels. In the present study, this hypothesis was addressed by evaluating the efficacy of six AEDs in wildtype and Pgp deficient Mdr1a/b(-/-) mice in the intrahippocampal kainate model of mesial temporal lobe epilepsy. In this model, frequent focal electrographic seizures develop after an initial kainate-induced status epilepticus. These seizures are resistant to major AEDs, but the mechanisms of this resistance are unknown. In the present experiments, the focal nonconvulsive seizures were resistant to carbamazepine and phenytoin, whereas high doses of valproate and levetiracetam exerted moderate and phenobarbital and diazepam marked anti-seizure effects. All AEDs suppressed generalized convulsive seizures. No significant differences between wildtype and Pgp-deficient mice were observed in anti-seizure drug efficacies. Also, the individual responder and nonresponder rates in each experiment did not differ between mouse genotypes. This does not argue against the multidrug transporter hypothesis in general, but indicates that Pgp is not involved in the mechanisms explaining that focal electrographic seizures are resistant to some AEDs in the intrahippocampal mouse model of partial epilepsy. This was substantiated by the finding that epileptic wildtype mice do not exhibit increased Pgp expression in this model.

Impact of Genetic Polymorphisms of ABCB1 (MDR1, P-Glycoprotein) on Drug Disposition and Potential Clinical Implications: Update of the Literature

ATP-binding cassette transporter B1 (ABCB1; P-glycoprotein; multidrug resistance protein 1) is an adenosine triphosphate (ATP)-dependent efflux transporter located in the plasma membrane of many different cell types. Numerous structurally unrelated compounds, including drugs and environmental toxins, have been identified as substrates. ABCB1 limits the absorption of xenobiotics from the gut lumen, protects sensitive tissues (e.g. the brain, fetus and testes) from xenobiotics and is involved in biliary and renal secretion of its substrates. In recent years, a large number of polymorphisms of the ABCB1 [ATP-binding cassette, sub-family B (MDR/TAP), member 1] gene have been described. The variants 1236C>T (rs1128503, p.G412G), 2677G>T/A (rs2032582, p.A893S/T) and 3435C>T (rs1045642, p.I1145I) occur at high allele frequencies and create a common haplotype; therefore, they have been most widely studied. This review provides an overview of clinical studies published between 2002 and March 2015. In summary, the effect of ABCB1 variation on P-glycoprotein expression (messenger RNA and protein expression) and/or activity in various tissues (e.g. the liver, gut and heart) appears to be small. Although polymorphisms and haplotypes of ABCB1 have been associated with alterations in drug disposition and drug response, including adverse events with various ABCB1 substrates in different ethnic populations, the results have been majorly conflicting, with limited clinical relevance. Future research activities are warranted, considering a deep-sequencing approach, as well as well-designed clinical studies with appropriate sample sizes to elucidate the impact of rare ABCB1 variants and their potential consequences for effect sizes.

Imaging the Impact of the P-Glycoprotein (ABCB1) Function on the Brain Kinetics of Metoclopramide

The effects of metoclopramide on the central nervous system (CNS) in patients suggest substantial brain distribution. Previous data suggest that metoclopramide brain kinetics may nonetheless be controlled by ATP-binding cassette (ABC) transporters expressed at the blood-brain barrier. We used (11)C-metoclopramide PET imaging to elucidate the kinetic impact of transporter function on metoclopramide exposure to the brain.

METHODS

(11)C-metoclopramide transport by P-glycoprotein (P-gp; ABCB1) and the breast cancer resistance protein (BCRP; ABCG2) was tested using uptake assays in cells overexpressing P-gp and BCRP. (11)C-metoclopramide brain kinetics were compared using PET in rats (n = 4-5) in the absence and presence of a pharmacologic dose of metoclopramide (3 mg/kg), with or without P-gp inhibition using intravenous tariquidar (8 mg/kg). The (11)C-metoclopramide brain distribution (VT based on Logan plot analysis) and brain kinetics (2-tissue-compartment model) were characterized with either a measured or an imaged-derived input function. Plasma and brain radiometabolites were studied using radio-high-performance liquid chromatography analysis.

RESULTS

(11)C-metoclopramide transport was selective for P-gp over BCRP. Pharmacologic dose did not affect baseline (11)C-metoclopramide brain kinetics (VT = 2.28 ± 0.32 and 2.04 ± 0.19 mL⋅cm(-3) using microdose and pharmacologic dose, respectively). Tariquidar significantly enhanced microdose (11)C-metoclopramide VT (7.80 ± 1.43 mL⋅cm(-3)) with a 4.4-fold increase in K1 (influx rate constant) and a 2.3-fold increase in binding potential (k3/k4) in the 2-tissue-compartment model. In the pharmacologic situation, P-gp inhibition significantly increased metoclopramide brain distribution (VT = 6.28 ± 0.48 mL⋅cm(-3)) with a 2.0-fold increase in K1 and a 2.2-fold decrease in k2 (efflux rate), with no significant impact on binding potential. In this situation, only parent (11)C-metoclopramide could be detected in the brains of P-gp-inhibited rats.

CONCLUSION

(11)C-metoclopramide benefits from favorable pharmacokinetic properties that offer reliable quantification of P-gp function at the blood-brain barrier in a pharmacologic situation. Using metoclopramide as a model of CNS drug, we demonstrated that P-gp function not only reduces influx but also mediates the efflux from the brain back to the blood compartment, with additional impact on brain distribution. This PET-based strategy of P-gp function investigation may provide new insight on the contribution of P-gp to the variability of response to CNS drugs between patients.