Cyclosporine A (CsA) affects the pharmacodynamics and pharmacokinetics of the atypical antipsychotic amisulpride probably via inhibition of P-glycoprotein (P-gp)

The Impact of P-Glycoprotein on CNS Drug Efflux and Variability in Response

Resistance against CNS drugs may arise from various mechanisms, with limited drug penetration across the blood-brain barrier (BBB) being a significant contributing factor. The BBB employs efflux transporters like P-glycoprotein (P-gp) to safeguard the brain by removing toxins and xenobiotics, however, P-gp also pumps out therapeutic drugs, and its upregulation in disease states can contribute to variability in drug response. While inhibiting P-gp to prevent drug efflux seems appealing, it could lead to toxicity since P-gp is also important for expulsion of toxins from the brain. This necessitates the incorporation of P-gp substrate liability assessment into early drug discovery stages using appropriate experimental approaches. Therefore, this review aims to draw interest in this crucial area by analyzing the existing research on P-gp's impact on brain distribution of major CNS drugs and exploring the detection methods for identifying P-gp substrates. By identifying confirmed P-gp substrates and evaluating effective detection methods, this work emphasizes the continued importance of monitoring P-gp-mediated CNS drug efflux out of the brain tissue. This knowledge can empower clinicians to anticipate potential treatment inefficacy and guide therapeutic decision-making, ultimately leading to improved patient treatment outcomes.

Age, Sex, and Comedication Effects on the Steady-State Plasma Concentrations of Amisulpride in Chinese Patients with Schizophrenia

BACKGROUND

Amisulpride, a second-generation atypical antipsychotic drug, was first marketed in Europe in the 1990s. This study aimed to provide a reference for the clinical application of amisulpride. The effects of age, sex, or specific comedications on amisulpride concentrations in Chinese patients with schizophrenia in the real world were investigated.

METHODS

A retrospective study was conducted of data on amisulpride based on the therapeutic drug monitoring service database at the Zigong Affiliated Hospital of Southwest Medical University.

RESULTS

Based on the inclusion criteria, 195 plasma samples from 173 patients (67.05% female and 32.95% male patients) were included for in-depth analysis. The median daily dose of amisulpride was 400 mg/d, median plasma concentration was 457.50 ng/mL, and median concentration/dose (C/D) ratio was 1.04 ng/mL/mg/d. The daily dose of amisulpride positively correlated with measured steady-state plasma concentrations. A significant difference was observed in the subgroup analysis of the combination with valproic acid, zopiclone, or aripiprazole on plasma concentrations. Combining amisulpride with these drugs increased the C/D ratios by 0.56-, 2.31-, and 0.77-fold, respectively. After adjusting for age, the median C/D ratio was found to be significantly different between female and male patients. However, no significant differences in daily dose, plasma concentration, and C/D ratio were noted with respect to sex and age of the patients.

CONCLUSIONS

Sex differences were inferred for the first time in this study, with differential effects on daily dose, steady-state plasma concentration, and C/D ratio associated with the population. In the included study samples, blood concentrations were distributed in the range of 223.25-823.55 ng/mL, which perhaps needs to be evaluated in line with the reference range of ammonia-sulfur ratios in the Chinese population.

Joint population pharmacokinetic modeling of venlafaxine and O-desmethyl venlafaxine in healthy volunteers and patients to evaluate the impact of morbidity and concomitant medication

Introduction: Venlafaxine (VEN) is a widely used dual selective serotonin/noradrenaline reuptake inhibitor indicated for depression and anxiety. It undergoes first-pass metabolism to its active metabolite, O-desmethyl venlafaxine (ODV). The aim of the present study was to develop a joint population pharmacokinetic (PPK) model to characterize their pharmacokinetic characters simultaneously. Methods: Plasma concentrations with demographic and clinical data were derived from a bioequivalence study in 24 healthy subjects and a naturalistic TDM setting containing 127 psychiatric patients. A parent-metabolite PPK modeling was performed with NONMEM software using a non-linear mixed effect modeling approach. Goodness of fit plots and normalized prediction distribution error method were used for model validation. Results and conclusion: Concentrations of VEN and ODV were well described with a one-compartment model incorporating first-pass metabolism. The first-pass metabolism was modeled as a first-order conversion. The morbid state and concomitant amisulpride were identified as two significant covariates affecting the clearance of VEN and ODV, which may account for some of the variations in exposure. This model may contribute to the precision medication in clinical practice and may inspire other drugs with pre-system metabolism.

Increased amisulpride serum concentration in a patient treated with concomitant pregabalin and trazodone: a case report

We report on the case of a 46-year-old woman with generalized anxiety disorder, paranoid personality disorder, and mild reduction in glomerular filtration rate (GFR). She was treated with pregabalin, trazodone, hydroxyzine, and clonazepam before hospital admission. Pharmacotherapy for the patient was changed during her first week in the hospital. Dosing of hydroxyzine and clonazepam was gradually decreased, and then these two drugs were withdrawn. Treatment with amisulpride was started on the fourth day after admission, and amisulpride serum levels were then measured three times as a part of therapeutic drug monitoring (TDM). The serum concentration of amisulpride detected during concurrent use of trazodone and pregabalin was approximately twice the therapeutic range for amisulpride. When the dose of pregabalin was reduced by half, the serum concentration of amisulpride decreased to therapeutic serum levels. We hypothesize that an interaction between amisulpride and pregabalin was responsible for the increased amisulpride concentration since both drugs are almost exclusively excreted from the body by the renal route. Pregabalin-amisulpride interaction might also be influenced by concomitant therapy with trazodone or a mild reduction in GFR. However, we only have clinical evidence for an interaction between amisulpride and pregabalin because after we halved the dose of pregabalin, the amisulpride concentration decreased, and the C/D ratio normalized. This could be helpful information for psychiatrists in order to avoid drug-drug interactions between amisulpride and pregabalin. We recommend TDM of amisulpride in patients treated concomitantly with other drugs eliminated mainly by the kidneys.

Modeling and Simulation for Individualized Therapy of Amisulpride in Chinese Patients with Schizophrenia: Focus on Interindividual Variability, Therapeutic Reference Range and the Laboratory Alert Level

PURPOSE

To explain the high inter-individual variability (IIV) and the frequency of exceeding the therapeutic reference range and the laboratory alert level of amisulpride, a population pharmacokinetic (PPK) model in Chinese patients with schizophrenia was built based on therapeutic drug monitoring (TDM) data to guide individualized therapy.

PATIENTS AND METHODS

Plasma concentration data (330 measurements from 121 patients) were analyzed using a nonlinear mixed-effects modeling (NONMEM) approach with first-order conditional estimation with interaction (FOCE I). The concentrations of amisulpride were detected by HPLC-MS/MS. Age, weight, sex, combination medication history and renal function status were evaluated as main covariates. The model was internally validated using goodness-of-fit, bootstrap and normalized prediction distribution error (NPDE). Recommended dosage regimens for patients with key covariates were estimated on the basis of Monte Carlo simulations and the established model.

RESULTS

A one-compartment model with first-order absorption and elimination was found to adequately characterize amisulpride concentration in Chinese patients with schizophrenia. The population estimates of the apparent volume of distribution (V/F) and apparent clearance (CL/F) were 12.7 L and 1.12 L/h, respectively. Age significantly affected the clearance of amisulpride and the final model was as follows: CL/F=1.04×(AGE/32)-0.624 (L/h). To avoid exceeding the laboratory alert level (640 ng/mL), the model-based simulation results showed that the recommended dose of amisulpride was no more than 600 mg/d for patients aged 60 years, 800 mg/d for those aged 40 years and 1200 mg/d for those aged 20 years, respectively.

CONCLUSION

Dosage optimization of amisulpride can be carried out according to age to reduce the risk of adverse reactions. The model can be used as a suitable tool for designing individualized therapy for Chinese patients with schizophrenia.

Active Transport of Hepatotoxic Pyrrolizidine Alkaloids in HepaRG Cells

1,2-unsaturated pyrrolizidine alkaloids (PAs) are secondary plant metabolites occurring as food contaminants that can cause severe liver damage upon metabolic activation in hepatocytes. However, it is yet unknown how these contaminants enter the cells. The role of hepatic transporters is only at the beginning of being recognized as a key determinant of PA toxicity. Therefore, this study concentrated on assessing the general mode of action of PA transport in the human hepatoma cell line HepaRG using seven structurally different PAs. Furthermore, several hepatic uptake and efflux transporters were targeted with pharmacological inhibitors to identify their role in the uptake of the PAs retrorsine and senecionine and in the disposition of their N-oxides (PANO). For this purpose, PA and PANO content was measured in the supernatant using LC-MS/MS. Also, PA-mediated cytotoxicity was analyzed after transport inhibition. It was found that PAs are taken up into HepaRG cells in a predominantly active and structure-dependent manner. This pattern correlates with other experimental endpoints such as cytotoxicity. Pharmacological inhibition of the influx transporters Na⁺/taurocholate co-transporting polypeptide (SLC10A1) and organic cation transporter 1 (SLC22A1) led to a reduced uptake of retrorsine and senecionine into HepaRG cells, emphasizing the relevance of these transporters for PA toxicokinetics.

A systematic review and combined meta-analysis of concentration of oral amisulpride

AIMS

Amisulpride, a first-line schizophrenia treatment, has shown large interindividual variability in plasma/serum levels, often outside the reference range (100-320 ng/mL). This study aims to clarify the impact of dose, sex, age and related factors for the interpatient variability in amisulpride plasma/serum concentration.

METHODS

Both English and Chinese databases were searched from their inception to May 16, 2019, using the terms: amisulpride and (plasma OR serum OR blood OR "drug monitoring" OR concentration). Studies reporting concentrations and either a dose, associated factor, clinical outcome or side effect were included.

RESULTS

Fourteen studies with 1628 participants were eventually included. Eligible articles yielded data on drug concentration and dose, averaging 333.9 (95% confidence interval [CI]: 294.5-373.3) ng/mL and 636.2 (95% CI: 549.7-722.6) mg/d, respectively. The calculated mean concentration-to-dose (C/D) ratio was 0.60 (95% CI: 0.52-0.67) (ng/mL)/mg. Subgroup analysis suggested that female patients on combined lithium-amisulpride have higher concentration levels and C/D ratios. Age was slight positive associated with C/D ratio while not for plasma level. Smoker patients have high concentration level than nonsmoking patients but not for C/D. Responsive and nonresponsive groups did not differ in concentration and C/D.

CONCLUSION

Pooled concentration levels of amisulpride were higher than recommended with wide individual variation, especially in older patients, female patients and patients taking amisulpride combined with lithium. The specific therapeutic reference range for amisulpride may require reconstruction, which should consider the influence of age, sex, kidney function, drug-drug interactions, different dose regimens and sampling times in future study.

KSP siRNA/paclitaxel-loaded PEGylated cationic liposomes for overcoming resistance to KSP inhibitors: Synergistic antitumor effects in drug-resistant ovarian cancer

Despite the promising anticancer effects of kinesin spindle protein (KSP) inhibition, functional plasticity of kinesins induced resistance against KSP inhibitors in a variety of cancers, leading to clinical failure. Additionally, paclitaxel is a widely used anticancer agent, but drug resistance has limited its use in the recurrent cancers. To overcome resistance against KSP inhibitors, we paired KSP inhibition with microtubule stabilization using KSP siRNA and paclitaxel. To enable temporal co-localization of both drugs in tumor cells in vivo, we exploited PEGylated cationic liposomes carrying both simultaneously. Drug synergism study shows that resistance against KSP inhibition can be suppressed by the action of microtubule-stabilizing paclitaxel, because microtubule stabilization prevents a different kinesin Kif15 from replacing all essential functions of KSP when KSP is inhibited. Our combination therapy showed more effective antiproliferative activity in vitro and in vivo than either paclitaxel or KSP siRNA alone. Ultimately, we could observe significantly improved therapeutic effects in the drug-resistant in vivo models, including cell line and patient-derived xenografts. Taken together, our combination therapy provides a potential anticancer strategy to overcome resistance against KSP inhibitors. Particularly, this strategy also provides an efficient approach to improve the therapeutic effects of paclitaxel in the drug-resistant cancers.

PLGA nanoparticles co-delivering MDR1 and BCL2 siRNA for overcoming resistance of paclitaxel and cisplatin in recurrent or advanced ovarian cancer

The inherent or acquired resistance to paclitaxel and cisplatin, which are commonly used chemotherapeutic agents for ovarian cancer treatment, remains an important issue in chemotherapy of multidrug resistant ovarian cancer. Currently, it is still challenging to deal with the recurrent or advanced stage ovarian cancer. When drug efflux and anti-apoptotic pathways are highly interdependent and also involved in developing the resistance of multidrug resistant ovarian cancer, simultaneous inhibition of both pathways represents the potential targets to enhance the efficacy of chemotherapy. Here, we introduce PLGA nanoparticles system as a “dual RNAi delivery system” to contain both MDR1 and BCL2 siRNA, which is designed for simultaneous inhibition of drug efflux and cell death defense pathways. In the present studies, siRNA-loaded PLGA nanoparticles efficiently elicit the simultaneous suppression of both genes, which consequently shows more enhanced drug-sensitivity than sole suppression of drug efflux or anti-apoptosis in the resistant ovarian cancer cells, owing to the interdependence of both pathways. Our siRNA-loaded PLGA nanoparticles for co-delivering MDR1 and BCL2 siRNA provide an efficient combination therapy strategy to overcome the chemoresistance of paclitaxel and cisplatin on the paclitaxel-resistant SKOV3-TR and cisplatin-resistant A2780-CP20 ovarian cancer respectively.

Managing interactions between cognitive enhancers and other psychotropics

Polypharmacy is common in psychiatry. Usage of cognitive enhancers is increasing in the psychiatric population. Many clinicians are not familiar with these new psychoactive compounds. This paper reviews the potential drug-drug interactions when these cognitive enhancers are used together with psychotropic drugs and their confounding effects on diagnosis and clinical management.

A RNA nanotechnology platform for a simultaneous two-in-one siRNA delivery and its application in synergistic RNAi therapy

Incorporating multiple copies of two RNAi molecules into a single nanostructure in a precisely controlled manner can provide an efficient delivery tool to regulate multiple gene pathways in the relation of mutual dependence. Here, we show a RNA nanotechnology platform for a two-in-one RNAi delivery system to contain polymeric two RNAi molecules within the same RNA nanoparticles, without the aid of polyelectrolyte condensation reagents. As our RNA nanoparticles lead to the simultaneous silencing of two targeted mRNAs, of which biological functions are highly interdependent, combination therapy for multi-drug resistance cancer cells, which was studied as a specific application of our two-in-one RNAi delivery system, demonstrates the efficient synergistic effects for cancer therapy. Therefore, this RNA nanoparticles approach has an efficient tool for a simultaneous co-delivery of RNAi molecules in the RNAi-based biomedical applications, and our current studies present an efficient strategy to overcome multi-drug resistance caused by malfunction of genes in chemotherapy.

An overview of the effective combination therapies for the treatment of breast cancer

Breast cancer (BC) is generally classified based on the receptors overexpressed on the cell nucleus, which include hormone receptors such as progesterone (PR) and estrogen (ER), and HER2. Triple-negative breast cancer (TNBC) is a type of cancer that lacks any of these three types of receptor proteins (ER/PR/HER2). Tumor cells exhibit drug resistant phenotypes that decrease the efficacy of chemotherapeutic treatments. Generally, drug resistance has a genetic basis that is caused by an abnormal gene expression, nevertheless, there are several types of drug resistance: efflux pumps reducing the cellular concentration of the drug, alterations in membrane lipids that reduce cellular uptake, increased or altered drug targets, metabolic alteration of the drug, inhibition of apoptosis, repair of the damaged DNA, and alteration of the cell cycle checkpoints. The use of "combination therapy" is recognized as an efficient solution to treat human diseases, in particular, breast cancer. In this review, we give examples of different nanocarriers used to co-deliver multiple therapeutics (chemotherapeutic agent and nucleic acid) to drug-resistant tumor cells, and lastly, we give our recommendations for the future directions for the co-delivery treatments.

Oral nanomedicine approaches for the treatment of psychiatric illnesses

Psychiatric illnesses are a leading cause of disability and morbidity globally. However, the preferred orally dosed pharmacological treatment options available for depression, anxiety and schizophrenia are often limited by factors such as low drug aqueous solubility, food effects, high hepatic first-pass metabolism effects and short half-lives. Furthermore, the discovery and development of more effective psychotropic agents has stalled in recent times, with the majority of new drugs reaching the market offering similar efficacy, but suffering from the same oral delivery concerns. As such, the application of nanomedicine formulation approaches to currently available drugs is a viable option for optimizing oral drug delivery and maximizing treatment efficacy. This review focuses on the various delivery challenges encountered by psychotropic drugs, and the ability of nanomedicine formulation strategies to overcome these. Specifically, we critically review proof of concept in vitro and in vivo studies of nanoemulsions/microemulsions, solid lipid nanoparticles, dendrimers, polymeric micelles, nanoparticles of biodegradable polymers and nanosuspensions, and provide new insight into the various mechanisms for improved drug performance. The advantages and limitations of current oral nanomedicine approaches for psychotropic drugs are discussed, which will provide guidance for future research directions and assist in fostering the translation of such delivery systems to the clinical setting. Accordingly, emphasis has been placed on correlating the in vitro/in vivo performance of these nanomedicine approaches with their potential clinical outcomes and benefits for patients.

Bypassing P-Glycoprotein Drug Efflux Mechanisms: Possible Applications in Pharmacoresistant Schizophrenia Therapy

The efficient noninvasive treatment of neurodegenerative disorders is often constrained by reduced permeation of therapeutic agents into the central nervous system (CNS). A vast majority of bioactive agents do not readily permeate into the brain tissue due to the existence of the blood-brain barrier (BBB) and the associated P-glycoprotein efflux transporter. The overexpression of the MDR1 P-glycoprotein has been related to the occurrence of multidrug resistance in CNS diseases. Various research outputs have focused on overcoming the P-glycoprotein drug efflux transporter, which mainly involve its inhibition or bypassing mechanisms. Studies into neurodegenerative disorders have shown that the P-glycoprotein efflux transporter plays a vital role in the progression of schizophrenia, with a noted increase in P-glycoprotein function among schizophrenic patients, thereby reducing therapeutic outcomes. In this review, we address the hypothesis that methods employed in overcoming P-glycoprotein in cancer and other disease states at the level of the BBB and intestine may be applied to schizophrenia drug delivery system design to improve clinical efficiency of drug therapies. In addition, the current review explores polymers and drug delivery systems capable of P-gp inhibition and modulation.

The poorly membrane permeable antipsychotic drugs amisulpride and sulpiride are substrates of the organic cation transporters from the SLC22 family

Variations in influx transport at the blood-brain barrier might affect the concentration of psychotropic drugs at their site of action and as a consequence might alter therapy response. Furthermore, influx transporters in organs such as the gut, liver and kidney may influence absorption, distribution, and elimination. Here, we analyzed 30 commonly used psychotropic drugs using a parallel artificial membrane permeability assay. Amisulpride and sulpiride showed the lowest membrane permeability (P e < 1.5 × 10(-6) cm/s) and will require influx transport to penetrate the blood-brain barrier and other physiological barriers. We then studied the uptake of amisulpride and sulpiride by the organic cation transporters of the SLC22 family OCT1, OCT2, OCT3, OCTN1, and OCTN2 Amisulpride was found to be transported by all five transporters studied. In contrast, sulpiride was only transported by OCT1 and OCT2. OCT1 showed the highest transport ability both for amisulpride (CLint = 1.9 ml/min/mg protein) and sulpiride (CLint = 4.2 ml/min/mg protein) and polymorphisms in OCT1 significantly reduced the uptake of both drugs. Furthermore, we observed carrier-mediated uptake that was inhibitable by known OCT inhibitors in the immortalized human brain microvascular endothelial cell line hCMEC/D3. In conclusion, this study demonstrates that amisulpride and sulpiride are substrates of organic cation transporters of the SLC22 family. SLC22 transporters may play an important role in the distribution of amisulpride and sulpiride, including their ability to penetrate the blood-brain barrier.

Reversible dimers of the atypical antipsychotic quetiapine inhibit p-glycoprotein-mediated efflux in vitro with increased binding affinity and in situ at the blood-brain barrier

The multidrug resistance transporter P-glycoprotein (P-gp) is highly expressed in the capillary endothelial cells of the blood-brain barrier (BBB) where it functions to limit the brain penetration of many drugs, including antipsychotic agents used to treat schizophrenia. Therefore, in an effort to inhibit the transporter, we designed dimers of the antipsychotic drug and P-gp substrate quetiapine (QT), linked by variable length tethers. In P-gp overexpressing cells and in human brain capillary endothelial hCMEC/D3 cells, the dimer with the shortest tether length (QT2C2) (1) was the most potent inhibitor showing >80-fold better inhibition of P-gp-mediated transport than monomeric QT. The dimers, which are linked via ester moieties, are designed to revert to the therapeutic monomer once inside the target cells. We demonstrated that the addition of two sterically blocking methyl groups to the linker (QT2C2Me2, 8) increased the half-life of the molecule in plasma 10-fold as compared to the dimer lacking methyl groups (QT2C2, 1), while retaining inhibitory potency for P-gp transport and sensitivity to cellular esterases. Experiments with purified P-gp demonstrated that QT2C2 (1) and QT2C2Me2 (8) interacted with both the H- and R-binding sites of the transporter with binding affinities 20- to 30-fold higher than that of monomeric QT. Using isolated rat brain capillaries, QT2C2Me2 (8) was a more potent inhibitor of P-gp transport than QT. Lastly, we showed that QT2C2Me2 (8) increased the accumulation of the P-gp substrate verapamil in rat brain in situ three times more than QT. Together, these results indicate that the QT dimer QT2C2Me2 (8) strongly inhibited P-gp transport activity in human brain capillary endothelial cells, in rat brain capillaries, and at the BBB in an animal model.

Impact of genetic deficiencies of P-glycoprotein and breast cancer resistance protein on pharmacokinetics of aripiprazole and dehydroaripiprazole

1. We investigated how deficiencies in P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) affect the pharmacokinetics of atypical antipsychotics aripiprazole and its active metabolite (dehydroaripiprazole) using normal Friend leukemia virus strain B (FVB) mice, BCRP knockout (Bcrp[-/-]) mice, and P-gp and BCRP triple knockout (Mdr1a/1b[-/-]Bcrp[-/-]) mice. 2. While plasma concentrations of aripiprazole and dehydroaripiprazole after oral administration were slightly higher in both Bcrp(-/-) and Mdr1a/1b(-/-)/Bcrp(-/-) mice than in normal FVB mice, the difference was not marked. The increase in absolute bioavailability (F) compared with normal mice (approximately 1.3-fold increase) was comparable between Bcrp(-/-) and Mdr1a/1b(-/-)/Bcrp(-/-) mice. This finding suggests that BCRP may be involved in the intestinal absorption of aripiprazole in mice, albeit with minimal contribution to absorption at best. 3. In contrast, the brain-to-plasma concentration ratio (Kp,brain) for aripiprazole and dehydroaripiprazole after oral administration was significantly higher in Mdr1a/1b(-/-)/Bcrp(-/-) mice than in normal mice, whereas Bcrp(-/-) mice exhibited Kp,brain values similar to those in normal mice. In addition, the Kp,brain values in Mdr1a/1b(-/-)/Bcrp(-/-) mice were not drastically different from those previously reported in Mdr1a/1b(-/-) mice, suggesting that brain penetration of aripiprazole and dehydroaripiprazole can be affected by P-gp, but with little synergistic effect of BCRP.

Evaluation of P-glycoprotein (abcb1a/b) modulation of [(18)F]fallypride in MicroPET imaging studies

[(18)F]Fallypride ([(18)F]FP) is an important and routinely used D2/D3 antagonist for quantitative imaging of dopaminergic neurotransmission in vivo. Recently it was shown that the brain uptake of the structurally related [(11)C]raclopride is modulated by P-glycoprotein (P-gp), an important efflux transporter at the blood-brain barrier. The purpose of this study was to determine whether the brain uptake of [(18)F]FP is influenced by P-gp. For examination of this possible modulation microPET studies were performed in a rat and a mouse model. Hence, [(18)F]FP was applied to Sprague Dawley rats, half of them being treated with the P-gp inhibitor cyclosporine A (CsA). In a second experimental series the tracer was applied to three different groups of FVB/N mice: wild type, P-gp double knockout (abcb1a/1b (-/-)) and CsA-treated mice. In CsA-treated Sprague Dawley rats [(18)F]FP showed an elevated standard uptake value in the striatum compared to the control animals. In FVB/N mice a similar effect was observed, showing an increasing uptake from wild type to CsA-treated and double knockout mice. Since genetically or pharmacologically induced reduction of P-gp activity increased the uptake of [(18)F]FP markedly, we conclude that [(18)F]FP is indeed a substrate of P-gp and that the efflux pump modulates its brain uptake. This effect - if true for humans - may have particular impact on clinical studies using [(18)F]FP for assessment of D2/3 receptor occupancy by antipsychotic drugs. This article is part of the Special Issue Section entitled 'Neuroimaging in Neuropharmacology'.

Drug-induced hypo- and hyperprolactinemia: mechanisms, clinical and therapeutic consequences

INTRODUCTION

The altered profiles of prolactin secretion in the anterior hypophysis, generated by pathological, pharmacological or toxicological causes, have special consequences on multiple functions in both genders.

AREAS COVERED

This selective review presents the main mechanisms controlling prolactin secretion, focusing on the interplay of various neurotransmitters or xenobiotics, but also on the role of psychic or posttraumatic stress. A detailed analysis of several pharmacotherapeutic groups with hyperprolactinemic effects emphasize on the relevance of the pharmacokinetic/pharmacodynamic mechanisms and the clinical significance of the long term administration.

EXPERT OPINION

Accurate monitoring and evaluation of the hyperprolactinemia induced by xenobiotics is strongly recommended. The typical antipsychotics and some of the atypical agents (amisulpride, risperidone, paliperidone), as well as some antidepressants, antihypertensives and prokinetics, are the most important groups inducing hyperprolactinemia. The hyperprolactinemic effects are correlated with their affinity for dopamine D2 receptors, their blood-brain barrier penetration and, implicitly, the requested dose for adequate occupancy of cerebral D2 receptors. Consequently, integration of available pharmacokinetic and pharmacodynamic data supports the idea of therapeutic switch to non-hyperprolactinemic agents (especially aripiprazole) or their association, for an optimal management of antipsychotic-induced hyperprolactinemia. Possible alternative strategies for counteracting the xenobiotics-induced hyperprolactinemia are also mentioned.

Effects of amisulpride and aripiprazole on progressive-ratio schedule performance: comparison with clozapine and haloperidol

Clozapine and some other atypical antipsychotics (e.g. quetiapine, olanzapine) have been found to exert a characteristic profile of action on operant behaviour maintained by progressive-ratio schedules, as revealed by Killeen's Mathematical Principles of Reinforcement model of schedule-controlled behaviour. These drugs increase the value of a parameter that expresses the 'incentive value' of the reinforcer (a) and a parameter that is inversely related to the organism's 'motor capacity' (δ). This experiment examined the effects of two further atypical antipsychotics, aripiprazole and amisulpride, on progressive-ratio schedule performance in rats; the effects of clozapine and a conventional antipsychotic, haloperidol, were also examined. In agreement with previous findings, clozapine (4, 8 mg kg⁻¹) increased a and δ, whereas haloperidol (0.05, 0.1 mg kg⁻¹) reduced a and increased δ. Aripiprazole (3,30 mg kg⁻¹) increased δ but did not affect a. Amisulpride (5, 50 mg kg⁻¹) had a delayed and protracted effect: δ was increased 3-6 hours after treatment; a was increased 1.5 hours, and reduced 12-24 hours after treatment. Interpretation based on Killeen's model suggests that aripiprazole does not share clozapine's ability to enhance reinforcer value. Amisulpride produced a short-lived enhancement, followed by a long-lasting reduction, of reinforcer value. Both drugs impaired motor performance.

In vitro P-glycoprotein efflux inhibition by atypical antipsychotics is in vivo nicely reflected by pharmacodynamic but less by pharmacokinetic changes

BACKGROUND

P-glycoprotein (P-gp), an efflux transporter of the blood-brain barrier, limits the access of multiple xenobiotics to the central nervous system (CNS). Thus drug-dependent inhibition, induction or genetic variation of P-gp impacts drug therapy.

METHODS

We investigated atypical antipsychotics and their interaction with P-gp. Amisulpride, clozapine, N-desmethylclozapine, olanzapine, and quetiapine were assessed in vitro on their inhibitory potential and in vivo on their disposition in mouse serum and brain, and behaviourally on the RotaRod test. In vivo wildtype (WT) and mdr1a/1b double knockout mice (mdr1a/1b (-/-, -/-); KO) were investigated.

RESULTS

In rhodamine 123 efflux assay drugs inhibitory potency to P-gp could be ranked quetiapine>N-desmethylclozapine>clozapine>olanzapine. When treating WT and KO mice i.p. and assessing brain and serum levels by HPLC analysis, P-gp expression has the highest but a rather short effect on the distribution of amisulpride, whereas the others ranked N-desmethylclozapine>olanzapine>quetiapine>clozapine; contrasted by in vivo behavioral changes at various time points. Here quetiapine>clozapine>olanzapine impacts behavior most when P-gp is lacking. Present results indicate the relevance of P-gp expression for CNS-drug therapy.

CONCLUSIONS

Combination of in vitro, and in vivo methods highlights that inhibitory potency did not reflect P-gp related drug disposition. But, when drugs were ranked for inhibitory potency, this order is reflected in pharmacodynamic changes or vice versa. Pharmacodynamic effects otherwise were at most correlated to drug brain levels, which however, were present only to a limited extent (by positron emission tomography) accessible in humans.

Relationship between P-glycoprotein and second-generation antipsychotics

The membrane transport protein P-glycoprotein (P-gp) is an interesting candidate for individual differences in response to antipsychotics. To present an overview of the current knowledge of P-gp and its interaction with second-generation antipsychotics (SGAs), an internet search for all relevant English original research articles concerning P-gp and SGAs was conducted. Several SGAs are substrates for P-gp in therapeutic concentrations. These include amisulpride, aripiprazole, olanzapine, perospirone, risperidone and paliperidone. Clozapine and quetiapine are not likely to be substrates of P-gp. However, most antipsychotics act as inhibitors of P-gp, and can therefore influence plasma and brain concentrations of other substrates. No information was available for sertindole, ziprasidone or zotepine. Research in animal models demonstrated significant differences in antipsychotic brain concentration and behavior owing to both P-gp knockout and inhibition. Results in patients are less clear, as several external factors have to be accounted for. Patients with polymorphisms which decrease P-gp functionality tend to perform better in clinical settings. There is some variability in the findings concerning adverse effects, and no definitive conclusions can be drawn at this point.

Estimation of rac-amisulpride transfer into milk and of infant dose via milk during its use in a lactating woman with bipolar disorder and schizophrenia

This case describes the transfer of the antipsychotic drug amisulpride into milk and the estimation of infant exposure via breastfeeding. The dyad investigated was a 28-year-old lactating woman and her 13-month-old daughter. The woman had been taking 400 mg of amisulpride daily for 9 days and provided eight milk samples and one blood sample over a 24-hour dose interval. Amisulpride concentrations in these samples were measured by high-performance liquid chromatography, and infant dose was calculated by standard methods. The infant's health and progress were evaluated by a neonatal pediatrician. Transfer of amisulpride into milk was high, with a milk:plasma distribution ratio of 19.5 (5,188 μg/L in milk and 266 μg/L in plasma). The average amisulpride concentration in milk was 3,562 μg/L, which, when multiplied by an average milk intake of 0.15 L/kg/day, gave an absolute infant dose of 534 μg/kg/day. The relative infant dose was 10.7% of the maternal weight-adjusted dose (5,000 μg/kg/day), which is slightly above the usual 10% safety recommendation. The infant was in good health with an appropriate Denver development score for her age. She showed no acute drug-related adverse effects. Given that the infant had already benefited from 13 months of breastfeeding, that amisulpride has potential adverse effects, and that its relative infant dose was 10.7%, we recommended cessation of breastfeeding in the near-term.

Chronic administration of cyclosporine A changes expression of BDNF and TrkB in rat hippocampus and midbrain

Neurotrophins, including the brain-derived neurotrophic factor (BDNF), are essential for regulating neuronal differentiation in developing brains. BDNF and its receptor tyrosine kinase receptor B (TrkB) are involved in neuronal signaling, survival and plasticity. Cyclosporine A (CsA) is a potent immunosuppressive agent which prevents allograft rejection in organ transplantation and various immunological diseases. We investigated whether chronic administration of CsA decreases BDNF gene expression in rats, and the influence of CsA on mRNA levels of TrkB receptors was also examined. For 30 days of CsA (10 mg/kg/day) administration, the expression of BDNF and TrkB mRNA was significantly decreased in the hippocampus and midbrain, but there was no significant difference in the cortex. CsA (0, 1, 5 10, 15 ug/ml) down-regulated BDNF and TrkB gene expression through cultured SH-SY5Y cells, as did all-trans retinoic acid (ATRA), and there was no effect on cell viability. These experimental results indicate that suppression of the BDNF and TrkB mRNA, protein level of BDNF expression in the hippocampus and midbrain may be related to altered behavior observed following chronic administration of CsA. A common mechanism of adverse effects of CsA induced depressive symptoms may involve neurotoxicity mediated by down-regulation of brain BDNF and TrkB.

Neuroleptic drugs revert the contextual fear conditioning deficit presented by spontaneously hypertensive rats: a potential animal model of emotional context processing in schizophrenia?

Schizophrenia, bipolar disorder, and attention deficit/hyperactivity disorder (ADHD) present abnormalities in emotion processing. A previous study showed that the spontaneously hypertensive rats (SHR), a putative animal model of ADHD, present reduced contextual fear conditioning (CFC). The aim of the present study was to characterize the deficit in CFC presented by SHR. Adult male normotensive Wistar rats and SHR were submitted to the CFC task. Sensitivity of the animals to the shock and the CFC performance after repeated exposure to the task were investigated. Pharmacological characterization consisted in the evaluation of the effects of the following drugs administered previously to the acquisition of the CFC: pentylenetetrazole (anxiogenic) and chlordiazepoxide (anxiolytic); methylphenidate and amphetamine (used for ADHD); lamotrigine, carbamazepine, and valproic acid (mood stabilizers); haloperidol, ziprasidone, risperidone, amisulpride, and clozapine (neuroleptic drugs); metoclopramide and SCH 23390 (dopamine antagonists without antipsychotic properties); and ketamine (a psychotomimmetic). The effects of paradoxical sleep deprivation (that worsens psychotic symptoms) and the performance in a latent inhibition protocol (an animal model of schizophrenia) were also verified. No differences in the sensitivity to the shock were observed. The repeated exposure to the CFC task did not modify the deficit in CFC presented by SHR. Considering pharmacological treatments, only the neuroleptic drugs reversed this deficit. This deficit was potentiated by proschizophrenia manipulations. Finally, a deficit in latent inhibition was also presented by SHR. These findings suggest that the deficit in CFC presented by SHR could be a useful animal model to study abnormalities in emotional context processing related to schizophrenia.

Psychotropic drugs and renal failure: translating the evidence for clinical practice

INTRODUCTION

The kidney is a primary route of drug elimination; abnormal kidney function is predicted to alter the pharmacokinetics of agents metabolized and/or excreted predominantly through this route. The high prevalence of mental disorders associated with psychotropic drug use in individuals with deteriorating renal function suggests there is a need to investigate the effects of renal failure on psychotropic pharmacokinetics. The aim of this review is to provide a clinically accessible overview of the effect of chronic renal failure on the pharmacokinetics for each of the major classes of prescribed psychotropic agents.

METHODS

All English language articles published between 1977 and 2008 were searched through PubMed, using the following keywords: "renal," "kidney," "pharmacokinetics," "renal impairment," "renal insufficiency," and "renal failure." Each of these search words was cross-referenced with the non-proprietary name of each psychotropic agent. The manufacturer's product insert was also reviewed for some agents for updated dosing. Owing to the lack of adequately powered studies, an inclusive manner was used.

RESULTS

Chronic renal failure variably affects the pharmacokinetic parameters of psychotropic drugs. A review of each psychotropic drug is provided, with an emphasis on the individual pharmacokinetic parameters and recommended dosing.

CONCLUSIONS

The adjudication of safe and effective doses for any psychotropic agent needs to be individualized. Tactics including dosage adjustment, slow titration, and careful monitoring for serious adverse events should be incorporated into practice.

Amisulpride the 'atypical' atypical antipsychotic--comparison to haloperidol, risperidone and clozapine

INTRODUCTION

Amisulpride's high and selective affinity for dopamine D2/3 (Ki 1.3/2.4 nM) receptors, lack of affinity for serotonin receptors, and its unusually high therapeutic doses (400-800 mg/day) makes it unique among atypical antipsychotics and prompted us to compare its actions with other antipsychotics in animal models.

METHODS

Amisulpride's effects on amphetamine and phencyclidine induced locomotor activity (AIL/PIL), conditioned avoidance response, catalepsy (CAT), subcortical Fos expression, and plasma prolactin was correlated to its time-course striatal D2/3 and prefrontal 5-HT2 receptor occupancy (D(2/3)/5-HT2RO); in comparison to haloperidol, clozapine, and risperidone.

RESULTS

Unlike the atypicals clozapine and risperidone, amisulpride lacked 5-HT2RO and showed a 'delayed' pattern of D2/3RO: 43, 60 and 88% after 1, 2 and 6 h (100 mg/kg), respectively, despite a quick onset (1 h) and decline (6 h) of prolactin elevation. While haloperidol and risperidone were effective at D2RO>60%, clozapine at D2/3RO<50%, amisulpride was effective only when its D2RO exceeded 60% with a delayed latency and lasted longer than other antipsychotics. CAT was observed for haloperidol and risperidone when D2RO exceeded 80%, while in the case of amisulpride, CAT was not observed even when doses exceeded 90% D2/3RO. Amisulpride also displayed functional limbic selectivity in Fos expression like the other atypicals.

CONCLUSIONS

Amisulpride's "delayed" functional profile on acute administration and the need for high doses is most likely due to its poor blood-brain-barrier penetration; however, it is distinct from other atypicals in showing low motor side-effects, activity against phencyclidine, and a mesolimbic preference, despite no action on serotonin receptors.

A review on the impact of P-glycoprotein on the penetration of drugs into the brain. Focus on psychotropic drugs

In recent years there has been increasing focus on the role of the drug transporter P-glycoprotein (P-gp) with regard to drug penetration into the brain. Studies using mice devoid of functional P-gp have revealed that P-gp at the blood-brain barrier (BBB) can exert a profound effect on the ability of some drugs to enter the brain, e.g. cardiovascular drugs (digoxin, quinidine), opioids (morphine, loperamide, methadone), HIV protease inhibitors, the new generation of antihistamines, and some antidepressants and antipsychotics. Among the latter group, risperidone is strongly influenced having about 10 times higher cerebral concentration in P-gp knock-out mice than in control mice. Taking into account that polytherapy is commonplace in psychiatry, theoretically there is a risk of drug-drug interactions with regard to P-gp at the BBB. Here we review the evidence for a role of P-gp with regard to psychoactive drugs from in vitro studies and experiments in knock-out mice devoid of functional P-gp. Moreover, the evidence for significant drug-drug interactions involving psychotropic drugs in rodents is considered. Clinical observations suggesting a role for P-gp in relation to drug-drug interactions at the BBB are sparse, and a definite conclusion awaits further studies. Also, the possible clinical relevance of P-gp genetic polymorphisms is questionable, and more investigations are needed on this subject.

Interactions of attention-deficit/hyperactivity disorder therapeutic agents with the efflux transporter P-glycoprotein

The objective of this study was to assess the potential interactions of the drug transporter P-glycoprotein with attention-deficit/hyperactivity disorder (ADHD) therapeutic agents atomoxetine--and the individual isomers of methylphenidate, amphetamine, and modafinil utilizing established in vitro assay. An initial ATPase assay indicated that both d- and l-methylphenidate have weak affinity for P-glycoprotein. The intracellular accumulation of P-glycoprotein substrates doxorubicin and rhodamine123 in the P-glycoprotein overexpressing cell line LLC-PK1/MDR1 was determined to evaluate potential inhibitory effects on P-glycoprotein. The results demonstrated that all compounds, except both modafinil isomers, significantly increased doxorubicin and rhodamine123 accumulation in LLC-PK1/MDR1 cells at higher concentrations. To investigate the P-glycoprotein substrate properties, the intracellular concentrations of the tested compounds in LLC-PK1/MDR1 and P-glycoprotein negative LLC-PK1 cells were measured in the presence and absence of the P-glycoprotein inhibitor PSC833. The results indicate that the accumulation of d-methylphenidate in LLC-PK1 cells was 32.0% higher than in LLC-PK1/MDR1 cells. Additionally, coadministration of PSC833 leads to 52.9% and 45.6% increases in d-modafinil and l-modafinil accumulation, respectively, in LLC-PK1/MDR1 cells. Further studies demonstrated that l-modafinil transport across LLC-PK1/MDR1 cell monolayers in the basolateral-to-apical (B-A) direction was significantly higher than in the apical-to-basolateral (A-B) direction. PSC833 treatment significantly decreased the transport of l-modafinil in B-A direction. In conclusion, our results suggest that all tested agents with the exception of modafinil isomers are relatively weak P-glycoprotein inhibitors. Furthermore, P-glycoprotein may play a minor role in the transport of d-methylphenidate, d-modafinil, and l-modafinil.

A Skin-Like Cytochrome P450 Cocktail Activates Prohaptens to Contact Allergenic Metabolites

Allergic contact dermatitis is a complex syndrome representing immunological responses to cutaneous exposure to protein-reactive chemicals. Although many contact sensitizers directly can elicit this disorder, others (prohaptens) require activation. Knowledge regarding the activating mechanisms remains limited, but one possibility is metabolic activation by cytochrome P450 (CYP) enzymes in the skin. We have, after quantitative reverse transcriptase-PCR studies of the CYP content in 18 human skin samples, developed an enriched skin-like recombinant human (rh) CYP cocktail using CYP1A1, 1B1, 2B6, 2E1, and 3A5. To validate the rhCYP cocktail, a prohaptenic conjugated diene ((5R)-5-isopropenyl-2-methyl-1-methylene-2-cyclohexene) was investigated using: the skin-like rhCYP cocktail, a liver-like rhCYP cocktail, single rhCYP enzymes, liver microsomes, keratinocytes, and a dendritic cell (DC) assay. The diene was activated to sensitizing epoxides in all non-cell-based incubations including the skin-like rhCYP cocktail. An exocyclic epoxide metabolite ((7R)-7-isopropenyl-4-methyl-1-oxaspiro[2.5]oct-4-ene) was found to be mainly responsible for the allergenic activity of the diene. This epoxide also induced pronounced DC activation indicated by upregulation of IL-8. The skin-like rhCYP cocktail provides a simplified alternative to using skin tissue preparations in mechanistic studies of CYP-mediated skin metabolism of prohaptens and offers the future possibility of designing in vitro predictive assays for assessment of allergenic activity of prohaptens.