Combined effects of epileptic seizure and phenobarbital induced overexpression of P-glycoprotein in brain of chemically kindled rats

SEW2871 reduces seizures via the sphingosine 1-phosphate receptor-1 pathway in the pentylenetetrazol and phenobarbitone kindling model of drug-refractory epilepsy

Epilepsy is a prevalent neurological disorder characterized by neuronal hypersynchronous discharge in the brain, leading to central nervous system (CNS) dysfunction. Despite the availability of anti-epileptic drugs (AEDs), resistance to AEDs is the greatest challenge in treating epilepsy. The role of sphingosine-1-phosphate-receptor 1 (S1PR1) in drug-resistant epilepsy is unexplored. This study investigated the effects of SEW2871, a potent S1PR1 agonist, on a phenobarbitone (PHB)-resistant pentylenetetrazol (PTZ)-kindled Wistar rat model. We measured the messenger ribonucleic acid (mRNA) expression of multi-drug resistance 1 (MDR1) and multi-drug resistance protein 5 (MRP5) as indicators for drug resistance. Rats received PHB + PTZ for 62 days to develop a drug-resistant epilepsy model. From day 48, SEW2871 (0.25, 0.5, 0.75 mg/kg, intraperitoneally [i.p.]) was administered for 14 days. Seizure scoring, behaviour, oxidative markers like reduced glutathione, catalase, superoxide dismutase, inflammatory markers like interleukin 1 beta tumour necrosis factor alpha, interferon gamma and mRNA expression (MDR1 and MRP5) were assessed, and histopathological assessments were conducted. SEW2871 demonstrated dose-dependent improvements in seizure scoring and neurobehavioral parameters with a reduction in oxidative and inflammation-induced neuronal damage. The S1PR1 agonist also downregulated MDR1 and MRP5 gene expression and significantly decreased the number of dark-stained pyknotic nuclei and increased cell density with neuronal rearrangement in the rat brain hippocampus. These findings suggest that SEW2871 might ameliorate epileptic symptoms by modulating drug resistance through downregulation of MDR1 and MRP5 gene expression.

Study of fingolimod, nitric oxide inhibitor, and P-glycoprotein inhibitor in modulating the P-glycoprotein expression via an endothelin-sphingolipid pathway in an animal model of pharmacoresistant epilepsy

BACKGROUND

The overexpression of P-glycoprotein (P-gp) contributes to drug resistance in patients with epilepsy, and the change of P-gp expression located at the blood-brain barrier alienates the anti-seizure effects of P-gp substrates. Thus, the present study explored the effect of fingolimod (FTY720) acting through an endothelin-sphingolipid pathway on P-gp-induced pentylenetetrazol (PTZ)-kindled phenobarbital (PB)-resistant rats.

MATERIALS AND METHODS

PTZ kindling (30 mg/kg; i.p.) and PB (40 mg/kg; orally) were used to develop an animal model of refractory epilepsy. The effect of Fingolimod on seizure score (Racine scale), plasma and brain levels of PB (high-performance liquid chromatography), and blood-brain barrier permeability (Evans blue dye) was determined. Further, Fingolimod's neuroprotective effect was determined by measuring the levels of various inflammatory cytokines, oxidative stress parameters, and neurotrophic factors in rat brain homogenate. The Fingolimod's effect on P-gp expression was estimated by reverse transcriptase-polymerase chain reaction and immunohistochemistry in rat brain. The H and E staining was done to determine the neuronal injury.

RESULTS

Fingolimod significantly (P < 0.001) reduced the seizure score in a dose-dependent manner and alleviated the blood-brain barrier permeability. It decreased the P-gp expression, which further increased the brain PB concentration. Fingolimod significantly (P < 0.01) reduced oxidative stress as well as inflammation. Moreover, it attenuated the raised neuronal injury score in a resistant model of epilepsy.

CONCLUSION

The modulation of the P-gp expression by Fingolimod improved drug delivery to the brain in an animal model of refractory epilepsy. Therefore, S1P signaling could serve as an additional therapeutic target to overcome refractoriness.

Pentylenetetrazole Induced Kindling Model of Refractory Epilepsy: A Proof-of-concept Study to Explore Dose and Time Range of Phenobarbital in Rats

Introduction

Drug-resistant epilepsy is an unmet medical condition that impacts 30% of epileptic patients. Numerous antiseizure drugs have already been developed but they provide only symptomatic relief and do not target the underlying pathogenesis. Preclinical models provide opportunities to gain insights into obscure mechanisms of drug-resistant epilepsy. Current animal models possess lacunae that need rectification and validation to discover novel antiepileptic drugs. The present study aims to validate 3 different doses of phenobarbital at 2 different periods.

Methods

Pentylenetetrazole was given at a sub-convulsive dose (30 mg/kg/day/intraperitoneal [IP]) for 28 days to develop kindling in male Wistar rats. Further, kindled rats were divided into the following four groups: Pentylenetetrazole control, pentylenetetrazole and phenobarbital (20 mg/kg), pentylenetetrazole and phenobarbital 40 mg/kg, and pentylenetetrazole and phenobarbital (60 mg/kg). They were assessed on days 14 and 28 post-kindling. Seizure scoring, oxidative stress, phenobarbital plasma levels, and histopathology of hippocampal neurons were analyzed.

Results

The results showed that the combination of pentylenetetrazole and phenobarbital (40 and 60 mg/kg) remarkably decreased seizure score, elucidated higher antioxidant effect, and prevented neuronal injury on day 14, whereas increased seizure score, oxidative stress, and neuronal death was observed with chronic administration of pentylenetetrazole and phenobarbital in kindled rats at day 28. Moreover, phenobarbital levels in blood were significantly increased at day 28 of phenobarbital treatment compared to day 14.

Conclusion

The adapted protocol with phenobarbital 40 mg/kg dose could be of great potential in screening antiseizure drugs in refractory epilepsy.

Intestinal Flora Composition Determines Microglia Activation and Improves Epileptic Episode Progress

In response to environmental stimuli, immune memory mediates the plasticity of myeloid cells. Immune training and immune tolerance are two aspects of plasticity. Microglia that are immunologically trained or immunologically tolerant are endowed with a tendency to differentiate into alternative dominant phenotypes (M1/M2). Male C57BL/6 mice (immune-training group, immune-tolerant group, and control group) were used to establish the kainic acid epilepsy model. The seizure grade, duration, latency, hippocampal potential, and energy density were used to evaluate seizures, and the changes in the polarization of microglia were detected by western blot. 16S rDNA sequencing showed that the abundance of Ruminococcus in the immune-tolerant group was the dominant flora. Our research connections Intestinal microorganisms, brain immune status, and epilepsy behavior together. Pro-inflammatory M1 phenotype and anti-inflammatory M2 phenotype mediate and enhance and suppress subsequent inflammation, respectively. We conclude that intestinal microorganisms influence the occurrence and development of epilepsy by regulating the polarization of microglia.

Edoxaban and the Issue of Drug-Drug Interactions: From Pharmacology to Clinical Practice

Edoxaban, a direct factor Xa inhibitor, is the latest of the non-vitamin K antagonist oral anticoagulants (NOACs). Despite being marketed later than other NOACs, its use is now spreading in current clinical practice, being indicated for both thromboprophylaxis in patients with non-valvular atrial fibrillation (NVAF) and for the treatment and prevention of venous thromboembolism (VTE). In patients with multiple conditions, the contemporary administration of several drugs can cause relevant drug-drug interactions (DDIs), which can affect drugs' pharmacokinetics and pharmacodynamics. Usually, all the NOACs are considered to have significantly fewer DDIs than vitamin K antagonists; notwithstanding, this is actually not true, all of them are affected by DDIs with drugs that can influence the activity (induction or inhibition) of P-glycoprotein (P-gp) and cytochrome P450 3A4, both responsible for the disposition and metabolism of NOACs to a different extent. In this review/expert opinion, we focused on an extensive report of edoxaban DDIs. All the relevant drugs categories have been examined to report on significant DDIs, discussing the impact on edoxaban pharmacokinetics and pharmacodynamics, and the evidence for dose adjustment. Our analysis found that, despite a restrained number of interactions, some strong inhibitors/inducers of P-gp and drug-metabolising enzymes can affect edoxaban concentration, just as it happens with other NOACs, implying the need for a dose adjustment. However, our analysis of edoxaban DDIs suggests that given the small propensity for interactions of this agent, its use represents an acceptable clinical decision. Still, DDIs can be significant in certain clinical situations and a careful evaluation is always needed when prescribing NOACs.

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.

Concomitant Use of Direct Oral Anticoagulants and Antiepileptic Drugs: A Prospective Cohort Study in Patients with Atrial Fibrillation

BACKGROUND

European guidelines do not recommend the use of carbamazepine, levetiracetam, phenobarbital, phenytoin, topiramate and valproic acid in patients taking direct oral anticoagulants (DOACs). Little is known regarding the clinical relevance of the interaction between DOACs and antiepileptic drugs.

OBJECTIVES

To evaluate the incidence of thromboembolic and bleeding events in patients with non-valvular atrial fibrillation (AF) concurrently treated with DOACs and antiepileptic drugs.

METHODS

This is a prospective multicentre cohort study of patients with non-valvular AF concurrently treated with DOACs and antiepileptic drugs. The primary outcome was ischaemic stroke/transient ischaemic attack (TIA)/systemic embolism (SE). Secondary outcome was major bleeding (MB). Incidence rates (% patient-year) were evaluated for the study outcomes.

RESULTS

Overall, 91 patients were included. Mean age was 78 ± 9.5 years, 49.5% were female. Mean CHA₂DS₂-VASc score was 4.76 ± 1.59 and mean HAS-BLED was 2.67 ± 1.26. Overall, 41, 20, 11, 10 and 9 out of 91 patients were treated with levetiracetam, valproic acid, phenobarbital, carbamazepine and other antiepileptic drugs, respectively. During a median follow-up of 17.5 ± 14.5 months, stroke/TIA/SE occurred in 9 patients (5.7% patient-year) and MB in 3 patients (1.9% patient-year). Ischaemic stroke was fatal in 3 patients (1.9% patient-year) and MB in one patient (0.6% patient-year).

CONCLUSION

In this cohort, patients with non-valvular AF treated with DOACs and antiepileptic drugs appear to have a relatively high rate of thromboembolic events.

Effects of Carbamazepine and Phenytoin on Pharmacokinetics and Pharmacodynamics of Rivaroxaban

Rivaroxaban (RIV) is commonly prescribed with carbamazepine or phenytoin (CBZ/PHT) in post-stroke seizure or post-stroke epilepsy patients. Although adverse events have been reported in several previous studies when they are coadministered, there are no studies of the interactions between these drugs. Therefore, our study was conducted to solve this lack of information. The potential effects of CBZ/PHT were investigated by comparing the pharmacokinetic (PK) and pharmacodynamic (PD) parameters of RIV between the control group (RIV alone) and the test groups (RIV administered with CBZ/PHT) in rats using the noncompartmental analysis (NCA) and the compartmental model approach. The NCA results indicate that AUC_t of RIV decreased by 57.9% or 89.7% and C_max of RIV decreased by 43.3% or 70.0% after administration of CBZ/PHT, respectively. In addition, both CBZ and PHT generally reduced the effects of RIV on the prothrombin times of the blood samples. PK profiles of RIV were most properly described by a two-compartment disposition model with a mixed first- and zero-order absorption kinetics and a first-order elimination kinetics. The compartmental model approach showed that a 211% or 1030% increase in CL/F of RIV and a 33.9% or 43.4% increase in D2 of RIV were observed in the test groups by the effects of CBZ/PHT, respectively. In conclusion, CBZ and PHT significantly reduced RIV exposure and therefore reduced the therapeutic effects of RIV. Consequently, this might result in adverse events due to insufficient RIV concentration to attain its therapeutic effects. Further studies are needed to validate this finding.

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.

Interaction of cyclosporine with phenobarbital in cats: a preliminary study

Phenobarbital (PB) decreases the cyclosporine (CsA) blood level in humans. However, the interaction of PB with CsA has not been reported in cats. This study investigated the effects of multiple doses of PB on the pharmacokinetics of CsA in three healthy cats. The treatments included oral CsA 5 mg/kg alone and oral CsA 5 mg/kg plus PB 5 mg/kg for 4 weeks. Co-administration of PB with CsA resulted in significant decreases in the oral bioavailability of CsA though both the first pass and elimination phases. These preliminary results suggest that oral administration of multiple doses of PB increases the required CsA dosage in CsA-based immunosuppressive therapy in cats.

Drug-Drug Interactions of P-gp Substrates Unrelated to CYP Metabolism

BACKGROUND

Recent US Food and Drug Administration (FDA) draft guidance on pharmacokinetic drugdrug interactions (DDIs) has highlighted the clinical importance of ABC transporters B1 or P-glycoprotein (P-gp), hepatic organic anion-transporting polypeptide transporters and breast cancer resistant protein because of their broad substrate specificity and the potential to be involved in DDIs. This guidance has indicated that digoxin, dabigatran etexilate and fexofenadine are P-gp substrate drugs and has defined P-gp inhibitors as those that increase the AUC of digoxin by ≧1.25-fold in clinical DDI studies. However, when substrate drugs of both CYPs and P-gp are involved in DDIs, it remains that the mechanisms of DDIs will be quite ambiguous in assessing how much the CYPs and/or drug transporters partially contribute to DDIs.

OBJECTIVE

Since there are no detailed manuscripts that summarizes P-gp interactions unrelated to CYP metabolism, this article reviews the effects of potent P-gp inhibitors and P-gp inducers on the pharmacokinetics of P-gp substrate drugs, including digoxin, talinolol, dabigatran etexilate, and fexofenadine in human studies. In addition, the present outcome were to determine the PK changes caused by DDIs among P-gp substrate drugs without CYP metabolism in human DDI studies.

CONCLUSION

Our manuscript concludes that the PK changes of the DDIs among P-gp drugs unrelated to CYP metabolism are less likely to be serious, and it appears to be convincing that the absences of clinical effects caused to the PK changes by the P-gp inducers is predominant compared with the excessive effects caused to those by the P-gp inhibitors.

Contributions of Drug Transporters to Blood-Brain Barriers

Blood-brain interfaces comprise the cerebral microvessel endothelium forming the blood-brain barrier (BBB) and the epithelium of the choroid plexuses forming the blood-cerebrospinal fluid barrier (BCSFB). Their main functions are to impede free diffusion between brain fluids and blood; to provide transport processes for essential nutrients, ions, and metabolic waste products; and to regulate the homeostasis of central nervous system (CNS), all of which are attributed to absent fenestrations, high expression of tight junction proteins at cell-cell contacts, and expression of multiple transporters, receptors, and enzymes. Existence of BBB is an important reason that systemic drug administration is not suitable for the treatment of CNS diseases. Some diseases, such epilepsy, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and diabetes, alter BBB function via affecting tight junction proteins or altering expression and function of these transporters. This chapter will illustrate function of BBB, expression of transporters, as well as their alterations under disease status.

Overview: Role of Drug Transporters in Drug Disposition and Its Clinical Significance

Absorption, distribution, and excretion of drugs are involved in drug transport across plasma membrane, most of which are mediated by drug transporters. These drug transporters are generally divided into solute carrier (SLC) family and ATP-binding cassette (ABC) family. These transporters not only mediate transport of therapeutic drugs across membrane but also transport various kinds of endogenous compounds. Thus besides being participated in disposal of drug and its clinical efficacy/toxicity, these transporters also play vital roles in maintaining cell homeostasis via regulating transport of endogenous compounds. This chapter will outline classification of drug transporters, their roles in drug disposal/drug response, and remote communication between tissues/organs.

ABC Family Transporters

The transport of specific molecules across lipid membranes is an essential function of all living organisms. The processes are usually mediated by specific transporters. One of the largest transporter families is the ATP-binding cassette (ABC) family. More than 40 ABC transporters have been identified in human, which are divided into 7 subfamilies (ABCA to ABCG) based on their gene structure, amino acid sequence, domain organization, and phylogenetic analysis. Of them, at least 11 ABC transporters including P-glycoprotein (P-GP/ABCB1), multidrug resistance-associated proteins (MRPs/ABCCs), and breast cancer resistance protein (BCRP/ABCG2) are involved in multidrug resistance (MDR) development. These ABC transporters are expressed in various tissues such as the liver, intestine, kidney, and brain, playing important roles in absorption, distribution, and excretion of drugs. Some ABC transporters are also involved in diverse cellular processes such as maintenance of osmotic homeostasis, antigen processing, cell division, immunity, cholesterol, and lipid trafficking. Several human diseases such as cystic fibrosis, sitosterolemia, Tangier disease, intrahepatic cholestasis, and retinal degeneration are associated with mutations in corresponding transporters. This chapter will describe function and expression of several ABC transporters (such as P-GP, BCRP, and MRPs), their substrates and inhibitors, as well as their clinical significance.

Pharmacokinetic Interactions of Clinical Interest Between Direct Oral Anticoagulants and Antiepileptic Drugs

Direct oral anticoagulants (DOACs), namely apixaban, dabigatran, edoxaban, and rivaroxaban are being increasingly prescribed among the general population, as they are considered to be associated to lower bleeding risk than classical anticoagulants, and do not require coagulation monitoring. Likewise, DOACs are increasingly concomitantly prescribed in patients with epilepsy taking, therefore, antiepileptic drugs (AEDs), above all among the elderly. As a result, potential interactions may cause an increased risk of DOAC-related bleeding or a reduced antithrombotic efficacy. The objective of the present review is to describe the pharmacokinetic interactions between AEDs and DOACs of clinical relevance. We observed that there are only few clinical reports in which such interactions have been described in patients. More data are available on the pharmacokinetics of both drugs classes which allow speculating on their potential interactions. Older AEDs, acting on cytochrome P450 isoenzymes, and especially on CYP3A4, such as phenobarbital, phenytoin, and carbamazepine are more likely to significantly reduce the anticoagulant effect of DOACs (especially rivaroxaban, apixaban, and edoxaban). Newer AEDs not affecting significantly CYP or P-gp, such as lamotrigine, or pregabalin are not likely to affect DOACs efficacy. Zonisamide and lacosamide, which do not affect significantly CYP activity in vitro, might have a quite safe profile, even though their effects on P-gp are not well-known, yet. Levetiracetam exerts only a potential effect on P-gp activity, and thus it might be safe, as well. In conclusion, there are only few case reports and limited evidence on interactions between DOACs and AEDs in patients. However, the overall evidence suggests that the interaction between these drug classes might be of high clinical relevance and therefore further studies in larger patients' cohorts are warranted for the future in order to better clarify their pharmacokinetic and define the most appropriate clinical behavior.

Alterations in Expression and Function of ABC Family Transporters at Blood-Brain Barrier under Liver Failure and Their Clinical Significances

Liver failure is often associated with hepatic encephalopathy, due to dyshomeostasis of the central nervous system (CNS). Under physiological conditions, the CNS homeostasis is precisely regulated by the blood-brain barrier (BBB). The BBB consists of brain microvessel endothelial cells connected with a junctional complex by the adherens junctions and tight junctions. Its main function is to maintain brain homoeostasis via limiting the entry of drugs/toxins to brain. The brain microvessel endothelial cells are characterized by minimal pinocytotic activity, absent fenestrations, and highly expressions of ATP-binding cassette (ABC) family transporters (such as P-glycoprotein, breast cancer resistance protein and multidrug resistance-associated proteins). These ABC transporters prevent brain from toxin accumulation by pumping toxins out of brain. Accumulating evidences demonstrates that liver failure diseases altered the expression and function of ABC transporters at The BBB, indicating that the alterations subsequently affect drugs’ brain distribution and CNS activity/neurotoxicity. ABC transporters also mediate the transport of endogenous substrates across the BBB, inferring that ABC transporters are also implicated in some physiological processes and the development of hepatic encephalopathy. This paper focuses on the alteration in the BBB permeability, the expression and function of ABC transporters at the BBB under liver failure status and their clinical significances.

Altered Function and Expression of ABC Transporters at the Blood-Brain Barrier and Increased Brain Distribution of Phenobarbital in Acute Liver Failure Mice

This study investigated alterations in the function and expression of P-glycoprotein (P-GP), breast cancer resistance protein (BCRP), and multidrug resistance-associated protein 2 (MRP2) at the blood–brain barrier (BBB) of acute liver failure (ALF) mice and its clinical significance. ALF mice were developed using intraperitoneal injection of thioacetamide. P-GP, BCRP, and MRP2 functions were determined by measuring the ratios of brain-to-plasma concentration of rhodamine 123, prazosin, and dinitrophenyl-S-glutathione, respectively. The mRNA and proteins expression levels of P-GP, BCRP, and MRP2 were evaluated with quantitative real-time PCR and western blot, respectively. MDCK-MDR1 and HCMEC/D3 cells were used to document the effects of the abnormally altered components in serum of ALF mice on the function and expression of P-GP. The clinical significance of alteration in P-GP function and expression was investigated by determining the distribution of the P-GP substrate phenobarbital (60 mg/kg, intravenous administration) in the brain and loss of righting reflex (LORR) induced by the drug (100 mg/kg). The results showed that ALF significantly downregulated the function and expression of both P-GP and BCRP, but increased the function and expression of MRP2 in the brain of mice. Cell study showed that increased chenodeoxycholic acid may be a reason behind the downregulated P-GP function and expression. Compared with control mice, ALF mice showed a significantly higher brain concentration of phenobarbital and higher brain-to-plasma concentration ratios. In accordance, ALF mice showed a significantly larger duration of LORR and shorter latency time of LORR by phenobarbital, inferring the enhanced pharmacological effect of phenobarbital on the central nervous system (CNS). In conclusion, the function and expression of P-GP and BCRP decreased, while the function and expression of MRP2 increased in the brain of ALF mice. The attenuated function and expression of P-GP at the BBB might enhance phenobarbital distribution in the brain and increase phenobarbital efficacy on the CNS of ALF mice.

The Alterations in the Expression and Function of P-Glycoprotein in Vitamin A-Deficient Rats as well as the Effect of Drug Disposition in Vivo

This study was aimed to investigate whether vitamin A deficiency could alter P-GP expression and function in tissues of rats and whether such effects affected the drug distribution in vivo of vitamin A-deficient rats. We induced vitamin A-deficient rats by giving them a vitamin A-free diet for 12 weeks. Then, Abcb1/P-GP expression was evaluated by qRT-PCR and Western blot. qRT-PCR analysis revealed that Abcb1a mRNA levels were increased in hippocampus and liver. In kidney, it only showed an upward trend. Abcb1b mRNA levels were increased in hippocampus, but decreased in cerebral cortex, liver and kidney. Western blot results were in good accordance with the alterations of Abcb1b mRNA levels. P-GP function was investigated through tissue distribution and body fluid excretion of rhodamine 123 (Rho123), and the results proclaimed that P-GP activities were also in good accordance with P-GP expression in cerebral cortex, liver and kidney. The change of drug distribution was also investigated through the tissue distribution of vincristine, and the results showed a significantly upward trend in all indicated tissues of vitamin A-deficient rats. In conclusion, vitamin A deficiency may alter Abcb1/P-GP expression and function in rat tissues, and the alterations may increase drug activity/toxicity through the increase of tissue accumulation.

Intractable epilepsy and the P-glycoprotein hypothesis

Epilepsy is a serious neurological disorder that affects more than 60 million people worldwide. Intractable epilepsy (IE) refers to approximately 20%-30% of epileptic patients who fail to achieve seizure control with antiepileptic drug (AED) treatment. Although the mechanisms underlying IE are not well understood, it has been hypothesized that multidrug transporters such as P-glycoprotein (P-gp) play a major role in drug efflux at the blood-brain barrier, and may be the underlying factor in the variable responses of patients to AEDs. The main goal of the present review is to show evidence from different areas that support the idea that the overexpression of P-gp is associated with IE. We discuss here evidence from animal studies, pharmacology, clinical cases and genetic studies.

Hyperammonemia enhances the function and expression of P-glycoprotein and Mrp2 at the blood-brain barrier through NF-κB

Ammonia is considered to be the main neurotoxin responsible for hepatic encephalopathy resulting from liver failure. Liver failure has been reported to alter expression and activity of P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (Mrp2) at the blood-brain barrier (BBB). The aim of this study was to investigate whether ammonia is involved in abnormalities of expression and activity of P-gp and Mrp2 at the BBB. Hyperammonemic rats were developed by an intraperitoneal injection of ammonium acetate (NH4 Ac, 4.5 mmol/kg). Results showed that Mrp2 function markedly increased in cortex and hippocampus of rats at 6 h following NH4 Ac administration. Significant increase in function of P-gp was observed in hippocampus of rats. Meanwhile, such alterations were in line with the increase in mRNA and protein levels of P-gp and Mrp2. Significant increase in levels of nuclear amount of nuclear factor-κB (NF-κB) p65 was also observed. Primarily cultured rat brain microvessel endothelial cells (rBMECs) were used for in vitro study. Data indicated that 24 h exposure to ammonia significantly increased function and expression of P-gp and Mrp2 in rBMECs, accompanied with activation of NF-κB. Furthermore, such alterations induced by ammonia were reversed by NF-κB inhibitor. In conclusion, this study demonstrates that hyperammonemia increases the function and expression of P-gp and Mrp2 at the BBB via activating NF-κB pathway. Hyperammonemia, a proverbial main factor responsible for neurocognitive disorder and blood-brain barrier (BBB) dysfunction resulting from liver failure, could increase the expression and activity of P-glycoprotein and multidrug resistance-associated protein 2 (Mrp2) at the BBB both in vivo and in vitro. Furthermore, the NF-κB activation stimulated by hyperammonemia may be the potential mechanism underlying such abnormalities induced by hyperammonemia.

Polymorphism of ABCB1/MDR1 C3435T in children and adolescents with partial epilepsy is due to different criteria for drug resistance - preliminary results

Background

The diagnosis of “drug resistance” in epilepsy can be defined and interpreted in various ways. This may be due to discrepant definitions of drug resistance to pharmacotherapy.

The aim of our study was to investigate the relationship between C3435T polymorphism of the MDR1 gene and drug resistance in epilepsy with the consideration of 4 different criteria for qualification to groups sensitive and resistant to applied pharmacotherapy.

Material/Methods

Evaluation of C3435T polymorphism of MDR1/ABCB1 gene was conducted on a group of 82 white children and young adolescents up to 18 years old. While qualifying the patients to the group of sensitive or drug resistant, the following 4 definitions of drug resistance were applied: the ILAE’s, Appleton’s, Siddiqui’s, and Berg’s.

Results

A detailed analysis of genotypes of the MDR1 gene did not show any significant discrepancies between the groups of patients resistant and sensitive to antiepileptic drugs (AEDs) in 4 consecutive comparisons taking into consideration various criteria of sensitivity and resistance to pharmacotherapy.

Conclusions

The obtained results clearly confirm the lack of a connection between the occurrence of drug-resistant epilepsy and C435T polymorphism of the MDR1 gene irrespective of the definition of drug resistance applied to the patient.

P-glycoprotein and multidrug resistance-associated protein 2 are oppositely altered in brain of rats with thioacetamide-induced acute liver failure

BACKGROUND

P-glycoprotein (P-GP) and multidrug resistance-associated protein 2 (MRP2) are involved in transport of many drugs across blood-brain barrier (BBB). The function and expression of P-GP and MRP2 may be modulated by different pathologies. Acute liver failure (ALF) was reported to impair BBB function, resulting in the increased BBB permeability.

AIMS

We investigated whether ALF altered function and expression of P-GP and MRP2 in brain of thioacetamide-induced ALF rats.

METHODS

ALF was induced by intraperitoneal injection of thioacetamide (300 mg/kg) for 2 days with a 24-h interval. The rats were used for experiments at 6, 12 and 24 h after the second administration. P-GP and MRP2 function in brain were determined using the brain-to-plasma ratios of corresponding substrates (rhodamine 123 and vincristine for P-GP; sulfobromophthalein and dinitrophenyl-S-glutathione for MRP2). Evans blue was used for examining the BBB integrity. Western blot was accomplished to determine P-GP and MRP2 protein expression.

RESULTS

The brain-to-plasma ratios of rhodamine 123 and vincristine were significantly increased in ALF-6 h rats and almost returned to normal levels in ALF-24 h rats, whereas those of sulfobromophthalein and dinitrophenyl-S-glutathione were decreased in all ALF rats. Western blot results showed that ALF decreased brain P-GP levels at 6 and 12 h, whereas increased MRP2 levels at 6, 12 and 24 h. No significant difference of Evans blue concentrations in brain was found among the four groups.

CONCLUSIONS

Function and expression of P-GP and MRP2 in brain of thioacetamide-induced ALF rats were oppositely altered.

Psychotropic drug-drug interactions involving P-glycoprotein

Multidrug resistance P-glycoprotein (P-gp; also known as MDR1 and ABCB1) is expressed in the luminal membrane of the small intestine and blood-brain barrier, and the apical membranes of excretory cells such as hepatocytes and kidney proximal tubule epithelia. P-gp regulates the absorption and elimination of a wide range of compounds, such as digoxin, paclitaxel, HIV protease inhibitors and psychotropic drugs. Its substrate specificity is as broad as that of cytochrome P450 (CYP) 3A4, which encompasses up to 50 % of the currently marketed drugs. There has been considerable interest in variations in the ABCB1 gene as predictors of the pharmacokinetics and/or treatment outcomes of several drug classes, including antidepressants and antipsychotics. Moreover, P-gp-mediated transport activity is saturable, and is subject to modulation by inhibition and induction, which can affect the pharmacokinetics, efficacy or safety of P-gp substrates. In addition, many of the P-gp substrates overlap with CYP3A4 substrates, and several psychotropic drugs that are P-gp substrates are also CYP3A4 substrates. Therefore, psychotropic drugs that are P-gp substrates may cause a drug interaction when P-gp inhibitors and inducers are coadministered, or when psychotropic drugs or other medicines that are P-gp substrates are added to a prescription. Hence, it is clinically important to accumulate data about drug interactions through studies on P-gp, in addition to CYP3A4, to assist in the selection of appropriate psychotropic medications and in avoiding inappropriate combinations of therapeutic agents. There is currently insufficient information available on the psychotropic drug interactions related to P-gp, and therefore we summarize the recent clinical data in this review.

Overexpression of multidrug resistance-associated protein 2 in the brain of pentylenetetrazole-kindled rats

Clinical studies and animal models have shown that pharmacoresistant epilepsy is partly due to the overexpression of ATP-binding cassette transporters at the brain. The purposes of the study were to investigate the function and expression of multidrug resistance-associated protein 2 (Mrp2) in the brain of pentylenetetrazole (PTZ)-kindled rats, and the effect of the altered Mrp2 function and expression on phenytoin (PHT) distribution in the brain. Kindled rats were developed by sub-convulsive dose of PTZ (33 mg/kg, every day, intraperitoneal (i.p.)) for 28 days. Mrp2 expression and function were measured by western blot and bromosulfophthalein (BSP) distribution in the brain. PHT concentrations in the brain of PTZ-kindled rats were measured alone or with co-administration of probenecid (50mg/kg). Further experiment was designed to investigate whether PHT treatment prevented the up-regulated brain Mrp2 expression and function induced by PTZ-kindling. The results showed that PTZ-kindling resulted in an increase of Mrp2 level in the hippocampus and cortex of rats, accompanied by significant decreases in the brain-to-plasma concentration ratio of BSP. PTZ-kindling also decreased PHT levels in the hippocampus and cortex without altering PHT concentrations in plasma, resulting in a lower brain-to-plasma concentration ratio of PHT. Co-administration of probenecid increased the brain-to-plasma ratio of BSP and PHT in the brain of both normal and PTZ-kindled rats. A 14-day PHT treatment prevented the up-regulation of Mrp2 expression and function induced by PTZ-kindling, accompanied by increases of PHT concentrations in the brain and good anticonvulsive effects. The present study demonstrated that chronic PTZ-kindling increased Mrp2 expression and function in the rat brain, and the up-regulation partly came from epileptic seizure.

Role of CNS efflux drug transporters in antiepileptic drug delivery: overcoming CNS efflux drug transport

Experimental support for the transporter hypothesis of drug resistance in epilepsies has triggered efforts developing and validating approaches to overcome enhanced blood-brain barrier efflux transport. Testing in rodent models has rendered proof-of-concept for an add-on therapy with antiepileptic drugs. However, further development of the approach would require tolerability considerations as efflux transporters serve an important protective function throughout the body limiting distribution of harmful xenobiotics. Relevant progress has been made in the elucidation of mechanisms driving up-regulation of the multidrug transporter P-glycoprotein in response to seizure activity. Based on this knowledge, novel strategies have been evaluated targeting the signaling cascade that regulates P-glycoprotein in the epileptic brain. Further concepts might include by-passing blood-brain barrier transporters by intracerebral administration or by encapsulation of antiepileptic drugs in nano-sized carrier systems. It is important to note that the future perspectives of respective approaches are still questionable based on the limited evidence for a clinical relevance of transporter expression. Thus, techniques are urgently needed for non-invasive assessment of blood-brain barrier transporter function. Respective techniques would allow testing for a clinical correlation between pharmacosensitivity and transporter function, validating therapeutic strategies targeting efflux transporters and selecting patients with transporter over-expression for respective clinical trials. Provided that further clinical data render support for the transporter hypothesis, the main question remains whether patients exist in which transporter over-expression is the predominant mechanism of drug resistance and in which overcoming drug efflux is equivalent with overcoming drug resistance. Imaging techniques might provide a tool to address these questions in clinical epileptology. However, the complex pharmacological interactions between antiepileptic drugs, radiotracers, and transporter modulators used in these approaches as well as interindividual differences in the brain pathology might hamper clear-cut conclusions and limit the diagnostic significance.

Tissue-specific alterations in expression and function of P-glycoprotein in streptozotocin-induced diabetic rats

AIM

To investigate the changes of expression and function of P-glycoprotein (P-GP) in cerebral cortex, hippocampus, liver, intestinal mucosa and kidney of streptozocin-induced diabetic rats.

METHODS

Diabetic rats were prepared via a single dose of streptozocin (65 mg/kg, ip). Abcb1/P-GP mRNA and protein expression levels in tissues were evaluated using quantitative real time polymerase chain reaction (QRT-PCR) analysis and Western blot, respectively. P-GP function was investigated via measuring tissue-to-plasma concentration ratios and body fluid excretion percentages of rhodamine 123.

RESULTS

In 5- and 8-week diabetic rats, Abcb1a mRNA levels were significantly decreased in cerebral cortices and intestinal mucosa, but dramatically increased in hippocampus and kidney. In liver, the level was increased in 5-week diabetic rats, and decreased in 8-week diabetic rats. Abcb1b mRNA levels were increased in cerebral cortex, hippocampus and kidney, but reduced in liver and intestinal mucosa in the diabetic rats. Western blot results were in accordance with the alterations of Abcb1a mRNA levels in most tissues examined. P-GP activity was markedly decreased in most tissues of diabetic rats, except kidney tissues.

CONCLUSION

Alterations in the expression and function of Abcb1/P-GP under diabetic conditions are tissue specific, Abcb1 specific and diabetic duration-dependent.