Pharmacological models in healthy volunteers: their use in the clinical development of psychotropic drugs

Pharmaco-EEG analysis of ligands varying in selectivity for α1 subunit-containing GABAA receptors during the active phase in rats

RATIONALE

Benzodiazepines are known to evoke changes in cortical electrophysiological activity that can be correlated with action at distinct γ-aminobutyric acid type A (GABAA) receptor subtypes.

OBJECTIVES

We used electroencephalography (EEG) paired with electromyography (EMG) to evaluate the role of α1 subunit-containing GABAA receptors (α1GABAARs) in benzodiazepine-induced sedation and changes in EEG band frequencies during the active phase of the light/dark cycle.

METHODS

Male Sprague-Dawley rats (N = 4/drug) were surgically instrumented with EEG/EMG electrodes. The rats were injected i.p. with zolpidem, an α1GABAAR-preferring compound, or L-838,417, which has selective efficacy for α2/3/5 subunit-containing GABAARs (i.e., α1GABAAR-sparing compound), in comparison with the non-selective benzodiazepine, triazolam.

RESULTS

All ligands evaluated induced changes in sleep-wake states during the active phase consistent with an increase in slow-wave sleep (SWS). The degree of SWS increase appeared to be related to the magnitude of delta power band changes induced by the ligands, with the strongest effects engendered by the α1GABAAR-preferring drug zolpidem and the weakest effects by the α1GABAAR-sparing compound, L-838,417. Consistent with other research, a selective increase in beta band power was observed with L-838,417, which may be associated with α2GABAAR-mediated anxiolysis.

CONCLUSIONS

Overall, these findings support the establishment of pharmaco-EEG "signatures" for identifying subtype-selective GABAA modulators in vivo.

Anxiolytic-like Effects and Quantitative EEG Profile of Palmitone Induces Responses Like Buspirone Rather Than Diazepam as Clinical Drugs

Anxiety is a mental disorder with a growing worldwide incidence due to the SARS-CoV-2 virus pandemic. Pharmacological therapy includes drugs such as benzodiazepines (BDZs) or azapirones like buspirone (BUSP) or analogs, which unfortunately produce severe adverse effects or no immediate response, respectively. Medicinal plants or their bioactive metabolites are a shared global alternative to treat anxiety. Palmitone is one active compound isolated from Annona species due to its tranquilizing activity. However, its influence on neural activity and possible mechanism of action are unknown. In this study, an electroencephalographic (EEG) spectral power analysis was used to corroborate its depressant activity in comparison with the anxiolytic-like effects of reference drugs such as diazepam (DZP, 1 mg/kg) and BUSP (4 mg/kg) or 8-OH-DPAT (1 mg/kg), alone or in the presence of the GABA_A (picrotoxin, PTX, 1 mg/kg) or serotonin 5-HT_1A receptor antagonists (WAY100634, WAY, 1 mg/kg). The anxiolytic-like activity was assayed using the behavioral response of mice employing open-field, hole-board, and plus-maze tests. EEG activity was registered in both the frontal and parietal cortex, performing a 10 min baseline and 30 min recording after the treatments. As a result, anxiety-like behavior was significantly decreased in mice administered with palmitone, DZP, BUSP, or 8-OH-DPAT. The effect of palmitone was equivalent to that produced by 5-HT_1A receptor agonists but 50% less effective than DZP. The presence of PTX and WAY prevented the anxiolytic-like response of DZP and 8-OH-DPAT, respectively. Whereas only the antagonist of the 5-HT_1A receptor (WAY) inhibited the palmitone effects. Palmitone and BUSP exhibited similar changes in the relative power bands after the spectral power analysis. This response was different to the changes induced by DZP. In conclusion, brain electrical activity was associated with the anxiolytic-like effects of palmitone implying a serotoninergic rather than a GABAergic mechanism of action.

Automated Interlaboratory Comparison of Therapeutic Drug Monitoring Data and Its Use for Evaluation of Published Therapeutic Reference Ranges

Therapeutic drug monitoring is a tool for optimising the pharmacological treatment of diseases where the therapeutic effect is difficult to measure or monitor. Therapeutic reference ranges and dose-effect relation are the main requirements for this drug titration tool. Defining and updating therapeutic reference ranges are difficult, and there is no standardised method for the calculation and clinical qualification of these. The study presents a basic model for validating and selecting routine laboratory data. The programmed algorithm was applied on data sets of antidepressants and antipsychotics from three public hospitals in Denmark. Therapeutic analytical ranges were compared with the published therapeutic reference ranges by the Arbeitsgemeinschaft für Neuropsychopharmakologie und Pharmakopsychiatrie (AGNP) and in additional literature. For most of the drugs, the calculated therapeutic analytical ranges showed good concordance between the laboratories and to published therapeutic reference ranges. The exceptions were flupentixol, haloperidol, paroxetine, perphenazine, and venlafaxine + o-desmethyl-venlafaxine (total plasma concentration), where the range was considerably higher for the laboratory data, while the calculated range of desipramine, sertraline, ziprasidone, and zuclopenthixol was considerably lower. In most cases, we identified additional literature supporting our data, highlighting the need of a critical re-examination of current therapeutic reference ranges in Denmark. An automated approach can aid in the evaluation of current and future therapeutic reference ranges by providing additional information based on big data from multiple laboratories.

Experimental Medicine Approaches in Early-Phase CNS Drug Development

Traditionally, Phase 1 clinical trials were largely conducted in healthy normal volunteers and focused on collection of safety, tolerability, and pharmacokinetic data. However, in the CNS therapeutic area, with more drugs failing in later phase development, Phase 1 trials have undergone an evolution that includes incorporation of novel approaches involving novel study designs, inclusion of biomarkers, and early inclusion of patients to improve the pharmacologic understanding of novel CNS-active compounds early in clinical development with the hope of improving success in later phase pivotal trials. In this chapter, the authors will discuss the changing landscape of Phase 1 clinical trials in CNS, including novel trial methodology, inclusion of pharmacodynamic biomarkers, and experimental medicine approaches to inform early decision-making in clinical development.

Differential effects of alkaloids on memory in rodents

Nicotinic acetylcholine receptors (nAChRs) play a critical role in the neuropharmacology of learning and memory. As such, naturally occurring alkaloids that regulate nAChR activity have gained interest for understanding and potentially improving memory function. In this study, we tested the acute effects of three known nicotinic alkaloids, nicotine, cotinine, and anatabine, in suppressing scopolamine-induced memory deficit in rodents by using two classic memory paradigms, Y-maze and novel object recognition (NOR) in mice and rats, respectively. We found that all compounds were able to suppress scopolamine-induced spatial memory deficit in the Y-maze spontaneous alternation paradigm. However, only nicotine was able to suppress the short-term object memory deficit in NOR, despite the higher doses of cotinine and anatabine used to account for their potential differences in nAChR activity. These results indicate that cotinine and anatabine can uniquely regulate short-term spatial memory, while nicotine seems to have more robust and general role in memory regulation in rodents. Thus, nAChR-activating alkaloids may possess distinct procognitive properties in rodents, depending on the memory types examined.

Atypical electrophysiological and behavioral responses to diazepam in a leading mouse model of Down syndrome

Mounting evidence implicates dysfunctional GABA_AR-mediated neurotransmission as one of the underlying causes of learning and memory deficits observed in the Ts65Dn mouse model of Down syndrome (DS). The specific origin and nature of such dysfunction is still under investigation, which is an issue with practical consequences to preclinical and clinical research, as well as to the care of individuals with DS and anxiety disorder or those experiencing seizures in emergency room settings. Here, we investigated the effects of GABA_AR positive allosteric modulation (PAM) by diazepam on brain activity, synaptic plasticity, and behavior in Ts65Dn mice. We found Ts65Dn mice to be less sensitive to diazepam, as assessed by electroencephalography, long-term potentiation, and elevated plus-maze. Still, diazepam pre-treatment displayed typical effectiveness in reducing susceptibility and severity to picrotoxin-induced seizures in Ts65Dn mice. These findings fill an important gap in the understanding of GABAergic function in a key model of DS.

Alprazolam-induced EEG spectral power changes in rhesus monkeys: a translational model for the evaluation of the behavioral effects of benzodiazepines

RATIONALE

Benzodiazepines induce electroencephalography (EEG) changes in rodents and humans that are associated with distinct behavioral effects and have been proposed as quantitative biomarkers for GABA_A receptor modulation. Specifically, central EEG beta and occipital EEG delta activity have been associated with anxiolysis and sedation, respectively. The extent to which nonhuman primates show the same dose- and topography-dependent effects remained unknown.

OBJECTIVES

We aimed at establishing a nonhuman primate model for the evaluation of benzodiazepine EEG pharmacology.

METHODS

Four adult male rhesus monkeys were prepared with fully implantable telemetry devices that monitored activity, peripheral body temperature, and contained two EEG (central and occipital), one electromyography (EMG), and one electrooculography channel. We investigated daytime alprazolam-induced changes in EEG spectral power, sleep-wake states, EMG activity, locomotor activity, and body temperature. Alprazolam (0.01-1.8 mg/kg, i.m.) or vehicle was administered acutely, and telemetry recording was conducted for 1 h.

RESULTS

Daytime alprazolam dose-dependently increased central EEG power (including beta activity), increased occipital EEG delta power, and decreased occipital EEG alpha, theta, and sigma power. There was an ~8-fold difference in the potency of alprazolam to increase central EEG beta vs. occipital EEG delta activity (based on relative EEG power). The highest dose, which increased both central EEG beta and occipital EEG delta relative power, induced sedative effects (increased time spent in N1 and N2 sleep stages) and decreased peripheral body temperature and locomotor activity.

CONCLUSIONS

Alprazolam induces dose- and topography-dependent EEG changes in rhesus monkeys and provides a valuable model for studying benzodiazepine pharmacology.

[Translational behavioral research using common marmosets in the psychiatric field]

The drug discovery activities for novel compounds with the superior efficacies to current drugs have been largely unsuccessful in the psychiatric field. One of the main reasons is the lack of appropriate behavioral assays and animal models for psychiatric disorders. Since the prefrontal cortex has great roles in their pathophysiology, non-human primate common marmosets with the well-developed prefrontal cortex would be useful as experimental animals in the future translational research. To measure objectively and quantitatively the psychiatric symptoms like motivational deficits, negative affective bias and cognitive impairments in patients with schizophrenia or major depressive disorder, the clinical laboratory tasks have been developed. The development of marmoset behavioral paradigms, which may correspond to the clinical laboratory tasks, have been progressed for the translational research. On the other hand, there are still limitations to develop the marmoset models resembling the pathophysiology of psychiatric disorders. We review the current state and future perspective of translational behavioral research using marmosets.

Effects of varenicline on alpha4-containing nicotinic acetylcholine receptor expression and cognitive performance in mice

Nicotinic acetylcholine receptor (nAChR) subtypes containing the α4 subunit, particularly α4β2 nAChRs, play an important role in cognitive functioning. The impact of the smoking cessation aid varenicline, a selective partial α4β2 nAChR agonist, on (1) changes of central protein and mRNA expression of this receptor and (2) on memory deficits in a mouse model of cognitive impairment was investigated. Protein and mRNA expression of both the α4 and β2 receptor subunits in mouse brain endothelial and hippocampal cells as well as hippocampus and neocortex tissues were determined by western blot and realtime PCR, respectively. The β2 antibody showed low specificity, though. Tissues were examined following a 2-week oral treatment with various doses of varenicline (0.01, 0.1, 1, 3 mg/kg/day) or vehicle. In addition, episodic memory of mice was assessed following this treatment with an object recognition task using (1) normal mice and (2) animals with anticholinergic-induced memory impairment (i.p. injection of 0.5 mg/kg scopolamine). Varenicline dose-dependently increased protein expression of both the α4 and β2 subunit in cell cultures and brain tissues, respectively, but had no effect on mRNA expression of both subunits. Scopolamine injection induced a significant reduction of object memory in vehicle-treated mice. By contrast, cognitive performance was not altered by scopolamine in varenicline-treated mice. In conclusion, a 2-week oral treatment with varenicline prevented memory impairment in the scopolamine mouse model. In parallel, protein, but not mRNA expression was upregulated, suggesting a posttranscriptional mechanism. Our findings suggest a beneficial effect of varenicline on cognitive dysfunction.

EEG-β/γ spectral power elevation in rat: a translatable biomarker elicited by GABA(Aα2/3)-positive allosteric modulators at nonsedating anxiolytic doses

Benzodiazepine drugs, through interaction with GABA(Aα1), GABA(Aα2,3), and GABA(Aα5) subunits, modulate cortical network oscillations, as reflected by a complex signature in the EEG power spectrum. Recent drug discovery efforts have developed GABA(Aα2,3)-subunit-selective partial modulators in an effort to dissociate the side effect liabilities from the efficacy imparted by benzodiazepines. Here, we evaluated rat EEG and behavioral end points during dosing of nine chemically distinct compounds that we confirmed statistically to selectively to enhance GABA(Aα2,3)-mediated vs. GABA(Aα1) or GABA(Aα5) currents in voltage clamped oocytes transfected with those GABA(A) subunits. These compounds were shown with in vivo receptor occupancy techniques to competitively displace [(3)H]flumazenil in multiple brain regions following peripheral administration at increasing doses. Over the same dose range, the compounds all produced dose-dependent EEG spectral power increases in the β- and and γ-bands. Finally, the dose range that increased γ-power coincided with that eliciting punished over unpunished responding in a behavioral conflict model of anxiety, indicative of anxiolysis without sedation. EEG γ-band power increases showed a significant positive correlation to in vitro GABA(Aα2,3) modulatory intrinsic activity across the compound set, further supporting a hypothesis that this EEG signature was linked specifically to pharmacological modulation of GABA(Aα2,3) signaling. These findings encourage further evaluation of this EEG signature as a noninvasive clinical translational biomarker that could ultimately facilitate development of GABA(Aα2,3)-subtype-selective drugs for anxiety and potentially other indications.

Use of translational pharmacodynamic biomarkers in early-phase clinical studies for schizophrenia

Schizophrenia is a severe mental disorder characterized by cognitive deficits, and positive and negative symptoms. The development of effective pharmacological compounds for the treatment of schizophrenia has proven challenging and costly, with many compounds failing during clinical trials. Many failures occur due to disease heterogeneity and lack of predictive preclinical models and biomarkers that readily translate to humans during early characterization of novel antipsychotic compounds. Traditional early-phase trials consist of single- or multiple-dose designs aimed at determining the safety and tolerability of an investigational compound in healthy volunteers. However, by incorporating a translational approach employing methodologies derived from preclinical studies, such as EEG measures and imaging, into the traditional Phase I program, critical information regarding a compound's dose-response effects on pharmacodynamic biomarkers can be acquired. Furthermore, combined with the use of patients with stable schizophrenia in early-phase clinical trials, significant 'de-risking' and more confident 'go/no-go' decisions are possible.

Impaired facial emotion recognition in a ketamine model of psychosis

OBJECTIVE

Social cognitive disabilities are a common feature in schizophrenia. Given the role of glutamatergic neurotransmission in schizophrenia-related cognitive impairments, we investigated the effects of the glutamatergic NMDA receptor antagonist ketamine on facial emotion recognition.

METHODS

Eighteen healthy male subjects were tested on two occasions, one without medication and one after administration with subanesthetic doses of intravenous ketamine. Emotion recognition was examined using the Ekman 60 Faces Test. In addition, attention was measured by the Continuous Performance Test (CPT), and psychopathology was rated using the Psychotomimetic States Inventory (PSI).

RESULTS

Ketamine produced a non-significant deterioration of global emotion recognition abilities. Specifically, the ability to correctly identify the facial expression of sadness was significantly reduced in the ketamine condition. These results were independent of psychotic symptoms and selective attention.

CONCLUSION

Our results point to the involvement of the glutamatergic system in the ability to recognize facial emotions.

Inhibition of cerebral type 1 cannabinoid receptors is associated with impaired auditory mismatch negativity generation in the ketamine model of schizophrenia

RATIONALE

Preclinical and clinical research suggests that the endogenous cannabinoid system is involved in cognitive impairments related to schizophrenia. In particular, the deficient generation of mismatch negativity (MMN) indicating auditory sensory memory is a characteristic finding in schizophrenic patients. Experimental studies implicate deficient N-methyl-D: -aspartate (NMDA) receptor functioning in such abnormalities.

OBJECTIVES

The primary aim of this study was to investigate the effects of the cannabinoid CB(1) receptor antagonist rimonabant on MMN deficits in the NMDA receptor antagonist model of schizophrenia by using ketamine.

METHODS

Twenty-four healthy male subjects participated in a randomized, double-blind, placebo-controlled cross-over study with subanesthetic doses of intravenous ketamine. The MMNs to frequency and duration deviants were elicited within an auditory oddball paradigm and recorded by a 32-channel EEG. Psychopathology was assessed using the Psychotomimetic States Inventory.

RESULTS

Twenty subjects completed both experimental sessions. Ketamine infusion had no significant effect on MMN amplitudes in both deviance conditions. In contrast to placebo, co-administration of rimonabant produced significant deficits in MMN amplitudes to duration deviants at electrode position Fz.

CONCLUSIONS

The results point to the involvement of the endogenous cannabinoid system in auditory sensory memory as a cognitive key feature in schizophrenia. They particularly suggest that CB(1) receptor antagonism may impair cognitive performance by a disturbed interaction between endocannabinergic activity and glutamatergic neurotransmission implied in schizophrenia.

Biomarkers in development of psychotropic drugs

Biomarkers have been receiving increasing attention, especially in the field of psychiatry. In contrast to the availability of potent therapeutic tools including pharmacotherapy, psychotherapy, and biological therapies, unmet needs remain in terms of onset of action, stability of response, and further improvement of the clinical course. Biomarkers are objectively measured characteristics which serve as indicators of the causes of illnesses, their clinical course, and modification by treatment. There exist a variety of markers: laboratory markers which comprise the determination of genetic and epigenetic markers, neurotransmitters, hormones, cytokines, neuropeptides, enzymes, and others as single measures; electrophysiological markers which usually comprise electroencephalography (EEG) measures, and in particular sleep EEG and evoked potentials, magnetic encephalography, electrocardiogram, facial electromyography, skin conductance, and others; brain imaging techniques such as cranial computed tomography, magnetic resonance imaging, functional MRl, magnetic resonance spectroscopy, positron emission tomography, and single photon emission computed tomography; and behavioral approaches such as cue exposure and challenge tests which can be used to induce especially emotional processes in anxiety and depression. Examples for each of these domains are provided in this review. With a view to developing more individually tailored therapeutic strategies, the characterization of patients and the courses of different types of treatment will become even more important in the future.

Modeling chronic olanzapine exposure using osmotic minipumps: pharmacological limitations

Animal models can face unique challenges in mirroring what occurs in humans. This is the case for antipsychotics in rodents, where these drugs are metabolized much more rapidly. One strategy to address this issue has been the use of osmotic minipumps to ensure continuous antipsychotic exposure over prolonged intervals, which is routinely the case when these same drugs are administered to humans. More recently, it has been identified that with olanzapine this approach may be compromised by oxidative degradation, a process that can be observed within days. Further, in vivo evidence has reported progressive decreases in plasma levels over a 1-month interval. To address this issue in vitro, osmotic minipumps (n=4), with olanzapine at a concentration resulting in a dose of 7.5mg/kg/day in vivo, were placed in saline-filled Falcon tubes and immersed in a water bath. Olanzapine concentrations were assessed in the minipumps as well as the surrounding water bath at baseline, 1h, and days 1, 7, 14, 21, and 28. Minipump results indicated a monophasic exponential decay and a half-life of 14.8 days (95% CI=13.1-17.1 days). Results from the water bath demonstrated a linear increase in olanzapine up to and including day 21, followed thereafter by a decrease to day 28. It is concluded that administration of olanzapine via osmotic minipump is viable in animal models to mirror what occurs in humans, although the interval should be confined to 2 weeks. As well, strategies in dissolving olanzapine to diminish oxidation are discussed.

Phase I trials: from traditional to newer approaches part II

In the first part of this series, the authors discussed strengths and weaknesses of traditional phase I drug development involving single ascending dose studies followed by multiple ascending dose studies in healthy volunteers. They then discussed how these traditional designs are being challenged by the development of truly novel molecular compounds that are not derived from earlier drugs and how the extent and design of phase I studies will need to be expanded and altered to investigate these novel compounds. In this column, the authors focus in more detail on limitations of traditional phase I studies for investigating truly novel compounds and propose solutions to address these problems. Adaptive trial designs and biomarker endpoints are discussed.

Anticholinergic drug use and risk for dementia: target for dementia prevention

An increasing number of longitudinal cohort studies have identified a risk increase for dementia by the chronic use of drugs with anticholinergic properties. The respective data from the German Study on Aging, Cognition and Dementia in Primary Care Patients (AgeCoDe) also showing risk increase (hazard ratio = 2.081) are reported here. The mechanisms by which the risk increase is transported are still unknown. Irritation of compensated alterations of cholinergic transmission at the pre-dementia stage of Alzheimer's disease (AD) or acceleration of neuroinflammation by disturbance of the anti-inflammatory effect of cholinergic innervation are discussed. In terms of dementia prevention, centrally acting anticholinergic drugs should be strictly avoided, because of long-term dementia risk increase in addition to acute negative effects on cognition.

Effects of lorazepam on brain activity pattern during an anxiety symptom provocation challenge

Human models of anxiety are useful to develop new effective anxiolytics. The objective of this study was to use functional magnetic resonance imaging (fMRI) to test the hypothesis that a single dose of lorazepam modifies brain activation during an anxiety challenge. Eighteen healthy male subjects underwent fMRI associated with a challenge based on the anticipation of aversive electrical stimulations after pretreatment, either with placebo or with 1.0 mg of oral lorazepam. Anxiety was rated before fMRI and after, referring to the threat condition periods, using State Trait Anxiety Inventory (STAI) and Hamilton scales. The conditioning procedure induced anxiety, as indicated by clinical rating score changes. Lorazepam did not modify anxiety rating as compared to placebo. Lorazepam reduced cerebral activity in superior frontal gyrus, anterior insula/inferior frontal gyrus and cingulate gyrus. The current finding provides the first evidence of the modulatory effects of an established anxiolytic agent on brain activation related to anticipatory anxiety.

Effects of dimethylaminoethanol pyroglutamate (DMAE p-Glu) against memory deficits induced by scopolamine: evidence from preclinical and clinical studies

RATIONALE

Dimethylaminoethanol pyroglutamate (DMAE p-Glu) is a compound resulting from the reaction between dimethylaminoethanol (an indirect precursor of acetylcholine) and pyroglutamic acid (a cyclic derivative of glutamic acid having procholinergic properties and promnesic effects in both animals and man).

OBJECTIVES

The present study undertook preclinical and clinical evaluations to test a potential therapeutic utility for DMAE p-Glu in cognitive impairments related to central cholinergic deficit.

MATERIALS AND METHODS

In preclinical study, DMAE p-Glu was studied in rats by intracerebral microdialysis in conscious freely moving animals, on performance of rats in the Morris water maze test of spatial memory, and on the deficit in passive avoidance behavior induced by scopolamine. The clinical study examined the effect of DMAE p-Glu on cognitive deficits induced by an intravenous injection of scopolamine in healthy young male subjects.

RESULTS

In rat experiments, DMAE p-Glu increased the extracellular levels of choline and acetylcholine in the medial prefrontal cortex, as assessed by intracerebral microdialysis, improved performance in a test of spatial memory, and reduced scopolamine-induced memory deficit in passive avoidance behavior. Clinical study results show that scopolamine induced a memory deficit and that DMAE p-Glu produced a significant positive effect on scores in the Buschke test, as well as a slight but significant difference on choice reaction time.

CONCLUSION

These results indicate that DMAE p-Glu reduces the deleterious effect of scopolamine on long-term memory in healthy volunteers and suggest that DMAE p-Glu might be effective in reducing memory deficits in patients with cognitive impairment.