Influence of ABCB1 (P-glycoprotein) haplotypes on nortriptyline pharmacokinetics and nortriptyline-induced postural hypotension in healthy volunteers

Contrasting ABCB1 pharmacogenetics and psychotropic responses in child and adolescent psychiatry: a case comparison

This case comparison illustrates pharmacogenetic testing in psychotropic and clinical management in relation to the ABCB1 gene, which encodes the P-glycoprotein transporter affecting blood-brain barrier (BBB) permeability. Two pediatric patients (9 and 11 years old) were selected for similar clinical presentations with opposing ABCB1 genotype, while they were identically matched for key CYP450, dopaminergic and serotonergic genes (CYP2C9, CYP2C19, DRD2, SLC6A4, 5HTR2A). Case A was functional for the ABCB1 gene (G/G rs1045642), suggesting that the BBB had a functional P-glycoprotein transporter. Case B was subfunctional for the ABCB1 gene (A/A rs1045642), suggesting that the patient's BBB may be permeable to psychotropic drugs. Case A had more medication trials and dose adjustments than Case B. Case A had two inpatient admissions and interspersed emergency room visits, while case B had none.

A functional polymorphism in the ATP-Binding Cassette B1 transporter predicts pharmacologic response to combination of nortriptyline and morphine in neuropathic pain patients

Many genetic markers have been associated with variations in treatment response to analgesics, but none have been assessed in the context of combination therapies. In this study, the treatment effects of nortriptyline and morphine were tested for an association with genetic markers relevant to pain pathways. Treatment effects were determined for single and combination therapies. A total of 24 functional single nucleotide polymorphisms were tested within the gene loci of mu-opioid receptor (OPRM1) gene locus, ATP-Binding Cassette B1 Transporter (ABCB1), Cytochrome P450 gene family (CYP2C19 and CYP2D6), catecholamine inactivator Catechol-O-Methyl Transferase (COMT), and serotonin receptor 2A (HTR2A). Genotyping was performed in a population of neuropathic pain patients who previously participated in a clinical trial. For monotherapy, neither nortriptyline nor morphine responses were associated with single nucleotide polymorphisms. However, for nortriptyline + morphine combination therapy, the single nucleotide polymorphism rs1045642 within the drug efflux pump ABCB1 transporter significantly predicted analgesic response. The presence of the C allele accounted for 51% of pain variance in this subgroup in response to combination treatment. The T-allele homozygotes demonstrated only 20% improvement in pain scores, whereas the C-allele homozygotes 88%. There was no significant contribution of rs1045642 to the medication side effects under all treatment conditions. The UK Biobank data set was then used to validate this genetic association. Here, patients receiving similar combination therapy (opioid + tricyclic antidepressant) carrying the C allele of rs1045642 displayed 33% fewer body pain sites than patients without that allele, suggesting better pain control. In all, our results show a robust effect of the rs1045642 polymorphism in response to chronic pain treatment with a nortriptyline + morphine combination.

Dynamic disequilibrium of macromolecular transport as possible mechanism for hydrocephalus associated with long-term spaceflight

Hydrocephalus associated with long term spaceflight (HALS) for missions lasting over five months is well described but poorly understood. While structural changes of the brain due to microgravitational forces affecting the circulation of cerebrospinal fluid (CSF) have been described as one potential cause, we propose an alternative hypothesis based on dynamic disequilibrium of macromolecular transport across the blood brain barrier. We propose that factors altering physiology under conditions of spaceflight such as microgravity, hypercapnia, venous hypertension, medications, and dietary substances contribute to increased protein load in the ventricles and/or contribute to impairment of transport out of the ventricles that results in HALS. Individual variation in the genetic expression of efflux transporters (p-glycoprotein) has been shown to correlate with the presence and degree of hydrocephalus in animal studies. We describe the evidence behind this concept and propose how these factors can be studied in order to determine the underlying pathogenesis which is imperative in order to cure or prevent HALS.

Distal tubule basolateral potassium channels: cellular and molecular mechanisms of regulation

PURPOSE OF REVIEW

Multiple clinical and translational evidence support benefits of high potassium diet; however, there many uncertainties underlying the molecular and cellular mechanisms determining effects of dietary potassium. Kir4.1 and Kir5.1 proteins form a functional heteromer (Kir4.1/Kir5.1), which is the primary inwardly rectifying potassium channel on the basolateral membrane of both distal convoluted tubule (DCT) and the collecting duct principal cells. The purpose of this mini-review is to summarize latest advances in our understanding of the evolution, physiological relevance and mechanisms controlling these channels.

RECENT FINDINGS

Kir4.1 and Kir5.1 channels play a critical role in determining electrolyte homeostasis in the kidney and blood pressure, respectively. It was reported that Kir4.1/Kir5.1 serves as potassium sensors in the distal nephron responding to variations in dietary intake and hormonal stimuli. Global and kidney specific knockouts of either channel resulted in hypokalemia and severe cardiorenal phenotypes. Furthermore, knock out of Kir5.1 in Dahl salt-sensitive rat background revealed the crucial role of the Kir4.1/Kir5.1 channel in salt-induced hypertension.

SUMMARY

Here, we focus on reviewing novel experimental evidence of the physiological function, expression and hormonal regulation of renal basolateral inwardly rectifying potassium channels. Further investigation of molecular and cellular mechanisms controlling Kir4.1 and Kir4.1/Kir5.1-mediating pathways and development of specific compounds targeting these channels function is essential for proper control of electrolyte homeostasis and blood pressure.

Nanomedicine applications in women's health: state of the art

State-of-the-art applications of nanomedicine have the potential to revolutionize the diagnosis, prevention, and treatment of a range of conditions and diseases affecting women’s health. In this review, we provide a synopsis of potential applications of nanomedicine in some of the most dominant fields of women’s health: mental health, sexual health, reproductive medicine, oncology, menopause-related conditions and dementia. We explore published studies arising from in vitro and in vivo experiments, and clinical trials where available, to reveal novel and highly promising therapeutic applications of nanomedicine in these fields. For the first time, we summarize the growing body of evidence relating to the use of nanomaterials as experimental tools for the detection, prevention, and treatment of significant diseases and conditions across the life course of a cisgender woman, from puberty to menopause; revealing the far-reaching and desirable theoretical impact of nanomedicine across different medical disciplines. We also present an overview of potential concerns regarding the therapeutic applications of nanomedicine and the factors currently restricting the growth of applied nanomedicine.

Nortriptyline, a tricyclic antidepressant, inhibits voltage-dependent K+ channels in coronary arterial smooth muscle cells

We demonstrated the effect of nortriptyline, a tricyclic antidepressant drug and serotonin reuptake inhibitor, on voltage-dependent K⁺ (Kv) channels in freshly isolated rabbit coronary arterial smooth muscle cells using a whole-cell patch clamp technique. Nortriptyline inhibited Kv currents in a concentration-dependent manner, with an apparent IC₅₀ value of 2.86±0.52 µM and a Hill coefficient of 0.77±0.1. Although application of nortriptyline did not change the activation curve, nortriptyline shifted the inactivation current toward a more negative potential. Application of train pulses (1 or 2 Hz) did not change the nortriptyline-induced Kv channel inhibition, suggesting that the effects of nortiprtyline were not use-dependent. Preincubation with the Kv1.5 and Kv2.1/2.2 inhibitors, DPO-1 and guangxitoxin did not affect nortriptyline inhibition of Kv channels. From these results, we concluded that nortriptyline inhibited Kv channels in a concentration-dependent and state-independent manner independently of serotonin reuptake.

ABCB1 genotyping in the treatment of depression

P-glycoprotein (P-gp), the gene product of ABCB1, is a drug transporter at the blood–brain barrier and could be a limiting factor for entrance of antidepressants into the brain, the target site of antidepressant action. Animal studies showed that brain concentrations of many antidepressants depend on P-gp. In humans, ABCB1 genotyping in the treatment of depression rests on the assumption that genetic variations in ABCB1 explain individual differences in antidepressant response via their effects on P-gp expression at the blood–brain barrier. High P-gp expression is hypothesized to lead to lower and often insufficient brain concentrations of P-gp substrate antidepressants. In this review, we summarize 32 studies investigating the question of whether ABCB1 polymorphisms predict clinical efficacy and/or tolerability of antidepressants in humans and evaluate the clinical application status of ABCB1 genotyping in depression treatment.

Pharmacogenetics and Treatment Response in Narcolepsy Type 1: Relevance of the Polymorphisms of the Drug Transporter Gene ABCB1

OBJECTIVE

Narcolepsy type 1 (NT1) is a chronic hypersomnia clinically characterized by daytime sleepiness and cataplexy. Narcolepsy type 1 treatments target individual symptoms: wake-promoting agents (eg, modafinil) are effective for sleepiness, antidepressants (eg, venlafaxine) on cataplexy, whereas sodium oxybate on both. Narcolepsy type 1 patients variably respond to modafinil and venlafaxine independently of individual clinical features.Given the potential influence of drug transmembrane transport (glycoprotein-P) on drug response, we explored the relation between genetic polymorphisms in the ABCB1 gene and clinical response to modafinil/venlafaxine in NT1.

METHODS

Individual drug response and genotypes were assessed in 107 NT1 patients (males/females, 64/43; mean age, 38 ± 21 years) treated with modafinil and/or venlafaxine at stable doses for at least 3 months. Minisequencing was performed to detect single-nucleotide polymorphisms in ABCB1. Patients with different responses to treatment were contrasted by Fisher exact test and multivariate analysis.

RESULTS

The ABCB1 diplotype was significantly associated with clinical response to modafinil, with the CGC-TTT (1236/2677/3435) being more frequent in the modafinil responder versus nonresponder group (P = 0.013). Conversely, no significant associations with clinical response to venlafaxine were found.

CONCLUSIONS

The ABCB1 variants modulate therapeutic response to modafinil and may partly explain pharmacoresistance in NT1 patients.

Association of ABCB1 gene variants, plasma antidepressant concentration, and treatment response: Results from a randomized clinical study

P-glycoprotein, encoded by the ABCB1 gene, functions as an ATP-driven efflux pump in the blood-brain barrier, extruding its substrates and thereby limiting their passage into the brain. ABCB1 polymorphisms predicted antidepressant drug response: Minor allele carriers of SNPs rs2032583 and rs2235015 had higher remission rates than major allele homozygotes. The aim of the current study was to evaluate an ABCB1 genotype-dependent efficacy of a quick dose escalation strategy. Depressed inpatients (n = 73) treated with antidepressants that are P-glycoprotein substrates were randomly assigned to a standard or high dose condition for 28 days. HAM-D scores, adverse effects and plasma antidepressant concentration were measured weekly and tested among two intronic SNPs rs2032583 and rs2235015. A treatment as usual control sample (n = 128) was retrospectively matched to the study group by gender, age, and diagnosis. There was a significant interaction of genotype x plasma antidepressant concentration: Minor allele carriers of rs2032583 [F(1,65) = 7.221, p = 0.009] and rs2235015 [F(1,65) = 4.939, p = 0.030] whose plasma drug concentration were within recommended range had a greater symptom reduction at study endpoint which exceeded the therapeutic benefit of the treatment as usual group [for rs2032583: F(1,163) = 4.366, p = 0.038]. Minor allele carriers of rs2032583 with high plasma drug levels had more sleep-related side effects than major allele homozygotes with high plasma drug levels. The treatment of MDD can be optimized by ABCB1 genotyping combined with monitoring of plasma drug concentrations: For minor allele carriers of rs2032583 and rs2235015, plasma antidepressant levels should not exceed the recommended range in order to obtain optimal treatment outcome.

A proposed role for efflux transporters in the pathogenesis of hydrocephalus

Hydrocephalus is a common brain disorder that is treated only with surgery. The basis for surgical treatment rests on the circulation theory. However, clinical and experimental data to substantiate circulation theory have remained inconclusive. In brain tissue and in the ventricles, we see that osmotic gradients drive water diffusion in water-permeable tissue. As the osmolarity of ventricular CSF increases within the cerebral ventricles, water movement into the ventricles increases and causes hydrocephalus. Macromolecular clearance from the ventricles is a mechanism to establish the normal CSF osmolarity, and therefore ventricular volume. Efflux transporters, (p-glycoprotein), are located along the blood brain barrier and play an important role in the clearance of macromolecules (endobiotics and xenobiotics) from the brain to the blood. There is clinical and experimental data to show that macromolecules are cleared out of the brain in normal and hydrocephalic brains. This article summarizes the existing evidence to support the role of efflux transporters in the pathogenesis of hydrocephalus. The location of p-gp along the pathways of macromolecular clearance and the broad substrate specificity of this abundant transporter to a variety of different macromolecules are reviewed. Involvement of p-gp in the transport of amyloid beta in Alzheimer disease and its relation to normal pressure hydrocephalus is reviewed. Finally, individual variability of p-gp expression might explain the variability in the development of hydrocephalus following intraventricular hemorrhage.

ABCB1 haplotypes are associated with P-gp activity and affect a major molecular response in chronic myeloid leukemia patients treated with a standard dose of imatinib

Despite the high efficacy of imatinib mesylate (IM) treatment for chronic myeloid leukemia (CML) patients, some individuals develop resistance due to impaired bioavailability. It has been previously demonstrated that the haplotypes for ATP-binding cassette subfamily B member 1 (ABCB1)with c.1236C>T, c.3435C>T and c.2677G>T/A polymorphisms markedly affect the secondary structure of ABCB1 mRNA and its activity. These modifications may affect efflux transporter activity and response to treatment with IM. The aim of the present study was to investigate the influence of ABCB1 haplotypes on P-glycoprotein (P-gp) activity, IM plasma levels and IM response. In total, 28 chronic-phase CML patients treated with a standard dose of IM (400 mg/day) were studied. The patients were selected according to the haplotypes of ABCB1, with c.1236C>T, c.3435C>T and c.2677G>T polymorphisms, and were classified into two groups based on the presence of the mutated allele in each genotype for the three ABCB1 polymorphisms. In addition, expression of P-gp and breakpoint cluster region-abelson 1 (BCR-ABL1), ABCB1 and solute carrier family 22 member 1 (SLC22A1) mRNA were evaluated. The P-gp activity in the wild-type group was found to be higher than that in the mutated group (59.1 vs. 38.3%; P=0.001). Furthermore, the patients who did not achieve major molecular response (MMR) showed a higher rate of efflux mediated by P-gp when compared with individuals who achieved MMR (64.7 vs. 45.7%; P=0.001). All patients without MMR demonstrated effluxes of >60%. In addition, patients without MMR exhibited lower plasma concentrations of IM compared with those with MMR (0.51 vs. 1.42 μg/ml; P=0.001). Higher levels of SLC22A1 mRNA were observed in patients who achieved MMR and complete molecular response (P<0.05). In conclusion, the ABCB1 1236CT/3435CT/2677GT and 1236TT/3435TT/2677TT haplotypes are associated with reduced P-gp activity and MMR in chronic-phase CML patients treated with a standard dose of IM.

Mechanisms of antidepressant resistance

Depression is one of the most frequent and severe mental disorder. Since the discovery of antidepressant (AD) properties of the imipramine and then after of other tricyclic compounds, several classes of psychotropic drugs have shown be effective in treating major depressive disorder (MDD). However, there is a wide range of variability in response to ADs that might lead to non response or partial response or in increased rate of relapse or recurrence. The mechanisms of response to AD therapy are poorly understood, and few biomarkers are available than can predict response to pharmacotherapy. Here, we will first review markers that can be used to predict response to pharmacotherapy, such as markers of drug metabolism or blood-brain barrier (BBB) function, the activity of specific brain areas or neurotransmitter systems, hormonal dysregulations or plasticity, and related molecular targets. We will describe both clinical and preclinical studies and describe factors that might affect the expression of these markers, including environmental or genetic factors and comorbidities. This information will permit us to suggest practical recommendations and innovative treatment strategies to improve therapeutic outcomes.

Association between genetic variation in the ABCB1 gene and switching, discontinuation, and dosage of antidepressant therapy: results from the Rotterdam Study

The objective of this study was to investigate whether polymorphisms in the ABCB1 gene were associated with switching, with discontinuation of antidepressants within 45 days after starting therapy, and/or with dose change in a large prospective population-based cohort study. Between April 1, 1991, and December 31, 2007, there were 1257 incident users of antidepressants with known ABCB1 genotypes (1236C>T, 2677G>T/A, 3435C>T) in the population-based Rotterdam Study. Logistic regression models were used to estimate the genotype and haplotype effect on the risk of switching and discontinuation. In addition, the association between the haplotypes and the prescribed drug dosage was assessed per drug class. The separate polymorphisms in the ABCB1 gene were associated with increased risks of switching and discontinuation but reached only statistical significance for the association between the 3435C>T polymorphism and switching. In a model adjusted for age and sex, homozygous carriers of the T-T-T haplotype had an increased risk of switching (odds ratio, 4.22; 95% confidence interval, 1.30-13.7; P = 0.017) and discontinuation (odds ratio, 1.47; 95% confidence interval, 0.98-2.22; P = 0.063). Explained variance was 10.4% for switching and 2.5% for discontinuation. In contrast, no association was observed between the T-T-T haplotype and the prescribed dosage. In summary, this study showed that genetic variation in the ABCB1 gene might play a role in the risk of switching and discontinuation of antidepressant therapy but the clinical relevance is limited.

ABCB1 polymorphism predicts escitalopram dose needed for remission in major depression

The ATP-binding cassette family of transporter proteins, subfamily B (MDR/TAP), member 1 (ABCB1) (P-glycoprotein) transporter is a key component of the blood-brain barrier. Many antidepressants are subject to ABCB1 efflux. Functional polymorphisms of ABCB1 may influence central nervous system bioavailability of antidepressants subject to efflux. Single-nucleotide polymorphisms (SNPs) at rs1045642 (C3435T) of ABCB1 have been associated with efflux pump efficiency. This may explain part of the interindividual variation in antidepressant dose needed to remit. Individuals (N=113) with DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition) major depressive disorder (MDD) were treated with escitalopram (ESC) or venlafaxine (VEN) over 8 weeks. The17-item Hamilton Depression Rating Scale was assessed serially, blind to genotype. SNP rs1045642 of ABCB1 along with two SNPs previously reported to be in linkage disequilibrium with it (rs2032582 and rs1128503) were genotyped. Demographic features, clinical features, P450 metabolizer status and 5-HTTLPR (serotonin-transporter-linked promoter region) genotype were controlled for. Carriers of rs1045642 TT needed on average 11 mg of ESC to remit, whereas TC and CC carriers required 24 and 19 mg, respectively (P=0.0001). This equates to a 2.0- (95% confidence interval=1.5-3.4; P<0.001) fold greater ESC dose needed to remit for C carriers compared with TT carriers at rs1045642. Of VEN-treated subjects carrying TT genotype at rs1045642, 73.3% remitted compared with 12.5% for CC genotype (odds ratio=6.69; 95% confidence interval=1.72-25.9, P=0.006). These data suggest that antidepressant dose needed to remit can be predicted by an ABCB1 SNP. This has the potential clinical translation implications for dose selection and remission from MDD.