Comparison of single-dose and extended methamphetamine administration on reversal learning in rats

Rationale

Protracted use of methamphetamine (mAMPH) can result in long-term impairments in cognitive function in humans. A previous study reported reversal-specific learning impairments in rats after a binge administration of mAMPH. Several studies show that extended exposure to mAMPH may confer protection against cognitive impairments and the insult to monoamine systems typically observed after larger binge doses.

Objectives

To explore this issue, we compared the effects of escalating and single doses of mAMPH (and saline, SAL) on retention, reversal learning, and post-mortem analysis of dopamine and serotonin transporters, DAT and SERT.

Methods

Rats learned to discriminate equiluminant stimuli and then were treated with either: (1) 4?weeks of mAMPH increasing by 0.3?mg/kg, culminating in 6?mg/kg (mAMPH_escal); (2) 4?weeks of SAL with a single dose of 6?mg/kg on the last day of treatment (mAMPH_single); or (3) 4?weeks of SAL. Following treatment, rats were tested on retention and reversal learning, with subsequent analysis of DAT and SERT binding across subregions of the striatum and frontoparietal cortex, respectively.

Results

Retention of the pretreatment discrimination was not significantly impaired in either mAMPH treatment group. A significant decrease in ventrolateral striatal DAT binding was observed only in the mAMPH_single group and frontoparietal SERT was unaffected by either mAMPH treatment. Both treatment groups demonstrated attenuated reversal learning, particularly on measures of accuracy and effort.

Conclusions

These results show that extended and single-dose pretreatment with mAMPH similarly and selectively affect reversal learning, even in the absence of significant DAT or SERT changes.     

Determination of dopamine D2 receptor occupancy by lurasidone using positron emission tomography in healthy male subjects

Rationale

A positron emission tomography (PET) study of dopamine D₂ receptor occupancy was conducted to support a rational dose selection for clinical efficacy studies with lurasidone, an atypical antipsychotic that was approved for the treatment of schizophrenia by the FDA in late 2010.

Objectives

To determine the dopamine D₂ receptor occupancy of lurasidone in the ventral striatum, putamen and caudate nucleus, and to characterize the relationship between lurasidone serum concentration and D₂ receptor occupancy.

Methods

A single oral dose of lurasidone (10, 20, 40, 60, or 80 mg) was administered sequentially to healthy male subjects (n?=?4 in each cohort). Two PET scans were performed. For each scan, 20 mCi of [¹¹C]raclopride was administered intravenously as a bolus injection, followed immediately by 90 min of PET scan acquisitions.

Results

The D₂ receptor occupancy levels were 41–43 % for 10 mg, 51–55 % for 20 mg, 63–67 % for 40 mg, 77–84 % for 60 mg, and 73–79 % for 80 mg of lurasidone. The relationship between D₂ receptor occupancy and the mean serum lurasidone concentration during the PET scan (C _PET) was similar for the putamen, caudate nucleus, and ventral striatum regions. Mean D₂ receptor occupancy levels correlated well with average peak serum concentration of lurasidone.

Conclusions

In healthy volunteers, single doses of lurasidone 40–80 mg resulted in D₂ receptor occupancy levels of >60 %, a level of receptor occupancy previously associated with clinical response for atypical antipsychotics.     

A reliable model of intravenous MDMA self-administration in naïve mice

Rationale

MDMA is one of the most widely consumed recreational drugs in Europe. However, the mechanisms involved in the reinforcing properties of MDMA are still unclear. In this sense, the establishment of a reliable model of MDMA self-administration in mice could represent an important approach to study the neuronal substrates associated with MDMA reward by using genetically modified mice.

Objectives

To develop a reliable model of operant intravenous MDMA self-administration in drug-naïve mice.

Materials and methods

Mice were trained to acquire intravenous self-administration of MDMA at different doses (0, 0.06, 0.125, 0.25, 0.5 and 1.0 mg/kg/infusion) on a FR1 schedule of reinforcement for 15 consecutive days. The motivational value of different doses of MDMA (0.125, 0.25 and 0.5 mg/kg/infusion) was then tested using a progressive ratio paradigm. Finally, [³H]-mazindol autoradiographic studies were carried out in order to quantitatively assess presynaptic dopamine transporter (DAT) binding sites in the striatum of mice trained to self-administer MDMA (0 and 1.0 mg/kg/infusion) during 15 days.

Results

The latency for discrimination between the active and inactive holes, as well as the number of animals acquiring stability criteria, varied as a function of the dose of MDMA. The mice responding for intermediate doses (0.125, 0.25 and 0.5 mg/kg/infusion) discriminated earlier than those responding for low (0.06 mg/kg/infusion) or high (1.0 mg/kg/infusion) doses. The percentage of animals achieving stability criteria increased with days of testing and was inversely proportional to the dose of MDMA. The breaking points achieved for doses of 0.125 and 0.25 mg/kg/infusion were significantly higher than for a dose of 0.5 mg/kg/infusion. No significant DAT neurotoxicity was observed in the striatum of animals self-administering MDMA at a dose of 1 mg/kg/infusion.

Conclusions

The present results show that MDMA can be reliably self-administered by drug-naïve mice.     

D2-receptor occupancy measurement of JNJ-37822681, a novel fast off-rate D2-receptor antagonist, in healthy subjects using positron emission tomography: single dose versus steady state and dose selection

Rationale

JNJ-37822681 is a highly selective, fast dissociating dopamine D₂-receptor antagonist being developed for the treatment of schizophrenia. A single dose [¹¹C]raclopride positron emission tomography (PET) imaging study had yielded an estimated clinical dose range. Receptor occupancy at steady state was explored to test the validity of the single-dose estimates during chronic treatment.

Objectives

The aims of this study are to characterize single and multiple dose pharmacokinetics and obtain striatal D₂-receptor occupancies to predict doses for efficacy studies and assess the safety and tolerability of JNJ-37822681.

Methods

An open-label single- and multiple-dose study with 10?mg JNJ-37822681 (twice daily for 13 doses) was performed in 12 healthy men. Twenty [¹¹C]raclopride PET scans (up to 60?h after the last dose) from 11 subjects were used to estimate D₂-receptor occupancy. A direct effect O _max model was applied to explore the relationship between JNJ-37822681 plasma concentration and striatal D₂-receptor occupancy.

Results

Steady state was reached after 4?C5?days of twice daily dosing. JNJ-37822681 plasma concentrations of 3.17 to 63.0?ng/mL resulted in D₂ occupancies of 0?% to 62?%. The concentration leading to 50?% occupancy was 18.5?ng/mL (coefficient of variation 3.9?%) after single dose and 26.0?ng/mL (8.2?%) at steady state. JNJ-37822681 was well tolerated.

Conclusions

Receptor occupancy after single dose and at steady state differed for JNJ-37822681 and the robustness of the estimates at steady state will be tested in phase 2 studies. Dose predictions indicated that 10, 20, and 30?mg JNJ-37822681 twice daily could be suitable for these studies.     

Availability of dopamine and serotonin transporters in opioid-dependent users—a two-isotope SPECT study

Rationale and objective

The aims of this study were to examine the differences between 32 opioid-dependent users treated with a very low dose of methadone or undergoing methadone-free abstinence and 32 controls.

Methods

SPECT analysis using [^99mTc] TRODAT-1 to assess striatal dopamine transporter (DAT) availability and [¹²³I] ADAM to assess midbrain serotonin transporter (SERT) availability were performed.

Results

Lower striatal DAT and midbrain SERT availabilities were noted in low-dose methadone users. History of metamphatamine use was associated with the lower striatal DAT. The striatal DAT of methadone-free abstainers was also lower than controls. The midbrain SERT availability tended to be higher in the methadone-free abstainers than the low-dose methadone users. The severity of depressive symptoms was negatively correlated with midbrain SERT availability in the opioid users.

Conclusion

The availability of striatal DAT tended to be, and the availability of midbrain SERT was, lower in the opioid users. History of metamphatamine use may confound the difference in straital DAT between controls and opioid users, as midbrain SERT and depressive symptoms are also associated with opioid use and abstinence.     

SERT and NET occupancy by venlafaxine and milnacipran in nonhuman primates: a PET study

Introduction

Serotonin and norepinephrine reuptake inhibitors (SNRIs) are antidepressants which have high affinity to both serotonin transporter (SERT) and norepinephrine transporter (NET). In studies in vitro, SNRIs have been reported to show a large variability in the affinity ratio between SERT and NET. For instance, the reported affinity ratio is about 30 for venlafaxine and 1.6 for milnacipran. In this study in nonhuman primates, we aimed to investigate the relationship between SERT and NET affinity by measuring the in vivo occupancy at both transporters of venlafaxine and milnacipran.

Methods

PET measurements with [¹¹C]MADAM and [¹⁸F]FMeNER-D₂ were performed in two female cynomolgus monkeys at baseline and after pretreatment with venlafaxine and milnacipran, respectively. Relationships between dose, plasma concentration, and transporter occupancy were evaluated by saturation analysis using a hyperbolic function. Binding affinity (Kd^plasma) was expressed by the dose or plasma concentration at which 50 % of the transporter was occupied.

Results

SERT and NET occupancy by venlafaxine and milnacipran increased in a dose and plasma concentration-dependent manner. The Kd^plasma ratio of SERT to NET was 1.9 for venlafaxine and 0.6 for milnacipran.

Conclusions

In this nonhuman primate PET study, the affinity in vivo for SERT and NET, respectively, was shown to be at a similar level for venlafaxine and milnacipran. Both drugs were found to produce balanced inhibition of SERT and NET binding. This observation is not consistent with previous in vitro binding data and illustrates the need to characterize antidepressants at in vivo condition.     

The interaction of escitalopram and R-citalopram at the human serotonin transporter investigated in the mouse

Rationale

Escitalopram appears to be a superior antidepressant to racemic citalopram. It has been hypothesized that binding of R-citalopram to the serotonin transporter (SERT) antagonizes escitalopram binding to and inhibition of the SERT, thereby curtailing the elevation of extracellular 5-hydroxytryptamine (5-HT_Ext), and hence antidepressant efficacy. Further, it has been suggested that a putative allosteric binding site is important for binding of escitalopram to the primary, orthosteric, site, and for R-citalopram’s inhibition hereof.

Objectives

Primary: Investigate at the human (h)SERT, at clinical relevant doses, whether R-citalopram antagonizes escitalopram-induced 5-HT_Ext elevation. Secondary: Investigate whether abolishing the putative allosteric site affects escitalopram-induced 5-HT_Ext elevation and/or modulates the effect of R-citalopram.

Methods

Recombinant generation of hSERT transgenic mice; in vivo microdialysis; SERT binding; pharmacokinetics; 5-HT sensitive behaviors (tail suspension, marble burying).

Results

We generated mice expressing either the wild-type human SERT (hSERT^WT) or hSERT carrying amino acid substitutions (A505V, L506F, I507L, S574T and I575T) collectively abolishing the putative allosteric site (hSERT^{ALI/VFL+SI/TT}). One mg/kg escitalopram yielded clinical relevant plasma levels and brain levels consistent with therapeutic SERT occupancy. The hSERT mice showed normal basal 5-HT_Ext levels. Escitalopram-induced 5-HT_Ext elevation was not decreased by R-citalopram co-treatment and was unaffected by loss of the allosteric site_. The behavioral effects of the clinically relevant escitalopram dose were small and tended to be enhanced by R-citalopram co-administration.

Conclusions

We find no evidence that R-citalopram directly antagonizes escitalopram or that the putative allosteric site is important for hSERT inhibition by escitalopram.     

Effect of a single-dose rifampin on the pharmacokinetics of pitavastatin in healthy volunteers

Purpose

As an inhibitor of HMG-CoA reductase that catalyses the first step of cholesterol synthesis, pitavastatin undergoes little hepatic metabolism; however, it is a substrate of uptake and efflux transporters. Since pitavastatin is potentially co-administered with agents that affect transporter activities, the pharmacokinetics of pitavastatin was investigated on the effects of a single-dose rifampin in healthy volunteers.

Methods

Twelve Chinese healthy male volunteers took 4 mg pitavastatin orally with 150 ml water or with a single dose of 600 mg rifampin on separate occasions and the plasma concentrations of pitavastatin were measured over 48 h by HPLC-MS/MS.

Results

A single dose of rifampin significantly increased the mean area under the plasma concentration-time curve(AUC)_(0-48h) and C_max of pitavastatin by 573.5 %(95%CI, 373.3–773.7 %, p?<?0.001) and 819.2 %(95 % CI, 515.4–1123.0 %, p?<?0.001) respectively, while significantly decreased the t_1/2 and CL/F of pitavastatin by 38.8 % (95 % CI, 18.2–59.4 %, p?<?0.001) and 81.4 % (95 % CI, 75.0–87.7 %, p?<?0.001) respectively.

Conclusions

Co-administration of pitavastatin with a single dose of rifampin resulted in a significant increase in plasma levels of pitavastatin in Chinese healthy subjects.     

The relationship between antipsychotic D2 occupancy and change in frontal metabolism and working memory

Rationale

The effects of aripiprazole on cognitive function are obscure, possibly due to the difficulty in disentangling the specific effects on cognitive function from effects secondary to the improvement of other schizophrenic symptoms. This prompts the necessity of using an intermediate biomarker relating the drug effect on the brain to change in cognitive function.

Objectives

To explore the effect of aripiprazole on cognitive function, we measured changes in frontal metabolism as an intermediate biomarker and sought to determine its relationship with D₂ receptor occupancy and changes in working memory.

Methods

Fifteen healthy male volunteers participated in the study. Serial positron emission tomography (PET) scans with [¹¹C]raclopride and [¹⁸?F]FDG were conducted 1 day before and 2 days after the administration of aripiprazole. The subjects performed the N-back task just after finishing the [¹⁸?F]FDG scan.

Results

The mean (±SD) D₂ receptor occupancies were 22.2?±?16.0 % in the 2 mg group, 35.5?±?3.6 % in the 5 mg group, 63.2?±?9.9 % in the 10 mg group and 72.8?±?2.1 % in the 30 mg group. The frontal metabolism was significantly decreased after the administration of aripiprazole (t?=?2.705, df?=?14, p?=?0.017). Greater striatal D₂ receptor occupancy was related to greater decrease in frontal metabolism (r?=??0.659, p?=?0.010), and greater reduction in frontal metabolism was associated with longer reaction times (r?=??0.597, p?=?0.019) under the greatest task load.

Conclusions

Aripiprazole can affect cognitive function and alter frontal metabolic function. The changes in these functions are linked to greater D₂ receptor occupancy. This suggests that it may be important to find the lowest effective dose of aripiprazole in order to prevent adverse cognitive effects.     

Effects of chronic fluoxetine treatment on serotonin 1B receptor-induced deficits in delayed alternation

Rationale

Obsessive-compulsive disorder (OCD) patients show overactivation of the orbitofrontal cortex and deficits in cognitive tasks that require proper orbitofrontal functioning including delayed alternation tests of spatial working memory. We recently showed that OCD-like behavior is induced in mice by activating orbitofrontal serotonin 1B receptors (5-HT1Bs). However, the role of 5-HT1Bs in delayed alternation remains unclear.

Objectives

We examined the effects of 5-HT1B receptor activation on delayed alternation task (DAT) performance. We also assessed the ability of an effective OCD treatment, fluoxetine, to prevent 5-HT1B-induced deficits in DAT performance.

Methods

Mice were tested on the DAT after acute treatment with saline, 3 or 6 mg/kg RU24969 (5-HT1B/1A agonist), 0.3 or 3 mg/kg 8-OH-DPAT (5-HT1A agonist), or co-injection with 3 mg/kg RU24969 and 5 mg/kg GR127935 (5-HT1B/1D antagonist). Separate mice were pretreated chronically (28 days) with 10 mg/kg fluoxetine and then tested on the DAT after acute treatment with 3 mg/kg RU24969, 0.3 mg/kg 8-OH-DPAT, or saline.

Results

Both doses of RU24969 decreased accuracy and increased latency on the DAT, and GR127935 blocked RU24969-induced effects on accuracy. The 0.3 mg/kg 8-OH-DPAT did not affect the DAT performance, whereas 3 mg/kg increased omissions on the DAT. Finally, RU24969-induced DAT deficits were absent in fluoxetine-pretreated mice.

Conclusions

We show that 5-HT1B receptor activation disrupts DAT performance in mice, and chronic fluoxetine pretreatment blocks these 5-HT1B-induced deficits. Our findings suggest that 5-HT1B receptors play an important role in modulating orbitofrontal-dependent delayed alternation. Moreover, 5-HT1B-induced DAT deficits may provide a mouse model for DAT deficits in OCD.     

Pharmacokinetic and pharmacodynamic effects of comedication of clopidogrel and dabigatran etexilate in healthy male volunteers

Purpose

To evaluate the pharmacokinetic and pharmacodynamic effects of concomitant administration of single loading doses of clopidogrel or multiple doses of clopidogrel with multiple doses of dabigatran etexilate.

Methods

This was an open-label trial in healthy male subjects. In part 1 (pilot, n?=?8) and part 3 (n?=?12), a single dose of clopidogrel (300 or 600 mg, respectively) was given concomitantly with dabigatran etexilate at steady state; part 2 was a randomized, multiple-dose, crossover study with the test treatment being clopidogrel at steady state [300 mg loading dose on day 1, then 75 mg once daily (qd)] with concomitant dabigatran.

Results

Bioavailability was moderately increased when a loading dose of clopidogrel (300 mg in part 1 and 600 mg in part 3) was administered concomitantly with dabigatran etexilate 150 mg twice daily (bid). Test/reference ratios for AUC_τ,ss were 135% (90% CI 107–169%) and 132% (90% CI 112–156%), respectively. Steady-state dosing of clopidogrel 75 mg qd and dabigatran etexilate 150 mg bid (part 2) demonstrated minor effects on dabigatran pharmacokinetics (AUC_τ,ss ratio test/reference: 91.9%, 90% CI 78.7–107%) or its pharmacokinetic/pharmacodynamic relationships (activated partial thromboplastin time, ecarin clotting time, thrombin time). Similarly, clopidogrel bioavailability remained unchanged by chronic administration of dabigatran etexilate (part 3: ratio test/reference for AUC_0?24 was 103%; 90% CI 80.3–131%), as did its pharmacodynamic effects on the inhibition of platelet aggregation.

Conclusions

When given concomitantly, dabigatran etexilate and clopidogrel at clinically relevant doses did not appear to have significant effects on the pharmacokinetic and pharmacodynamic profiles of either agent.     

Pharmacokinetic–Pharmacodynamic Relationships of Macitentan,a New Endothelin Receptor Antagonist,After Multiple Dosing in Healthy Korean Subjects

Background and objectives

Macitentan is a novel dual endothelin (ET)-1 receptor antagonist to be used in patients with pulmonary arterial hypertension. This study aimed to assess the pharmacokinetics (PK) and pharmacodynamics (PD) of macitentan after administration of multiple doses to healthy Korean male subjects.

Methods

A randomized, double-blind, placebo-controlled, multiple-ascending dose study was performed in 30 healthy male subjects receiving oral macitentan (3, 10, or 30 mg) or placebo once daily for 10 days. Plasma concentrations of macitentan, its active metabolite ACT-13277, and ET-1 were evaluated. Safety and tolerability measurements were conducted throughout the study.

Results

The concentration–time profile of macitentan was characterized by slow absorption (median time to maximum plasma concentration [t _max] 9–10 h) and slow elimination (mean elimination half-life [t _½] 11–15 h). After repeated doses of 3, 10, and 30 mg of macitentan over the course of 10 days, the peak concentration (C _max) increased as the dose increased and the area under the plasma concentration–time curve during the dosing interval (AUC _τ ) increased in a dose-proportional manner. Plasma concentrations showed approximately 1.5- to 1.9-fold accumulation on day 10 compared with day 1. ACT-132577 showed higher levels of exposure than macitentan, its mean half-life was 46–48 h, and it accumulated 7- to 12-fold. Macitentan increased plasma ET-1 concentrations at all doses tested and was well tolerated and elicited no serious adverse events.

Conclusion

Multiple oral doses of 3, 10, and 30 mg of macitentan were well tolerated in healthy Korean subjects, and its pharmacokinetics correlated positively with ET-1 concentrations.     

Single ascending oral dose pharmacokinetics and pharmacodynamics study of EV-077: the specific inhibitor of prostanoid- and isoprostane-induced cellular activation

Purpose

This study was performed to determine the oral pharmacokinetics (PK) of EV-077 and its effects on pharmacodynamic (PD) markers. EV-077 blocks prostanoid-induced and isoprostane-induced cellular activation, and is in development for the treatment of vascular inflammation and associated complications of type-2 diabetes..

Methods

This single-ascending-dose mono-centre study was randomised, placebo-controlled, and double-blinded within each dose group. Seven EV-077 doses were administered sequentially as an oral solution: 0.0125, 0.125, 0.375, 0.75, 1.25, 1.875 and 2.5 mg/kg body weight. PK, platelet aggregation, bleeding time and safety parameters were measured. Seven to eight healthy male subjects were dosed per group: five to six subjects received EV-077 and two subjects received placebo.

Results

Tmax was reached rapidly between 0.5 h and 1.0 h. Both Cmax and AUC increased linearly with the dose. The apparent terminal half-life (t½z) increased with the dose, most likely reflecting the increasing last quantifiable concentration with increasing dose; at 2.5 mg/kg, it was 2.7-6.9 h. Measurement of platelet aggregation showed no effect at 0.0125 mg/kg, and a full and reversible inhibition at doses of 0.125-2.5 mg/kg. The average bleeding time was dose-dependently prolonged, but was always below 9 min. The PK/PD profile showed that at plasma concentrations above 20 ng/ml, EV-077 platelet aggregation was completely inhibited (>90 %). All tested doses were well tolerated.

Conclusions

Orally administered EV-077 was well tolerated, readily absorbed, reached Cmax within 1 h, with a linear PK based on Cmax and AUC. The inhibition of platelet aggregation was complete and reversible at doses of 0.125 mg/kg and higher, and average bleeding time was below 9 min.     

Dopamine D2/3 occupancy of ziprasidone across a day: a within-subject PET study

Rationale

Ziprasidone is an atypical antipsychotic recommended to be administered twice daily.

Objectives

The purpose of this study was to investigate whether occupancy of the dopamine D_2/3 receptors by ziprasidone is maintained across a day employing a within subject design.

Methods

Positron emission tomography (PET) scans with [¹¹C]-raclopride were performed in 12 patients with schizophrenia while treated with ziprasidone 60 mg twice daily. Each patient completed [¹¹C]-raclopride PET scans at 5, 13 and 23 h after the last dose of ziprasidone. Dopamine D_2/3 receptor occupancy was estimated with reference to binding potential data of 44 age- and sex-matched control subjects in the caudate, putamen and ventral striatum.

Results

Eleven scans were available at each time point, and the mean occupancies at 5-, 13- and 23-h scans were 66, 39 and 2 % in the putamen; 62, 35 and ?6 % in the caudate; and 68, 47 and 11 % in the ventral striatum, respectively. The time-course of receptor occupancy across the regions indicated an occupancy half-life of 8.3 h. The serum level of ziprasidone associated with 50 % D_2/3 receptors occupancy was estimated to be 204 nmol/L (84 ng/ml). Prolactin levels were highest at 5-h post-dose and none showed hyperprolactinemia at 23-h scans.

Conclusions

The absence of ziprasidone striatal D_2/3 receptor binding 23 h after taking 60 mg under steady-state conditions is consistent with its peripheral half-life. The results support our earlier report that ziprasidone 60 mg administered twice daily appears to be the minimal dose expected to achieve therapeutic central dopamine D_2/3 receptor occupancy (i.e. 60 %). Clinical Trials Registration: 24-Hour Time Course of Striatal Dopamine D₂ Receptor Occupancy of Ziprasidone: A PET Study, www.clinicaltrials.gov/ct2/show/NCT00818298, NCT00818298     

Yohimbine increases opioid-seeking behavior in heroin-dependent, buprenorphine-maintained individuals

Rationale

In laboratory animals, the biological stressor yohimbine (α₂-noradrenergic autoreceptor antagonist) promotes drug seeking. Human laboratory studies have demonstrated that psychological stressors can increase drug craving but not that stressors alter drug seeking.

Objectives

This clinical study tested whether yohimbine increases opioid-seeking behavior.

Methods

Ten heroin-dependent, buprenorphine-stabilized (8 mg/day) volunteers sampled two doses of hydromorphone [12 and 24 mg IM in counterbalanced order, labeled drug A (session 1) and drug B (session 2)]. During each of six later sessions (within-subject, double-blind, randomized crossover design), volunteers could respond on a 12-trial choice progressive ratio task to earn units (1 or 2 mg) of the sampled hydromorphone dose (drug A or B) vs money ($2) following different oral yohimbine pretreatment doses (0, 16.2, and 32.4 mg).

Results

Behavioral economic demand intensity and peak responding (O _max) were significantly higher for hydromorphone 2 than 1 mg. Relative to placebo, yohimbine significantly increased hydromorphone demand inelasticity, more so for hydromorphone 1-mg units (P _max?=?909, 3,647, and 3,225 for placebo, 16.2, and 32.4 mg yohimbine doses, respectively) than hydromorphone 2-mg units (P _max?=?2,656, 3,193, and 3,615, respectively). Yohimbine produced significant but clinically modest dose-dependent increases in blood pressure (systolic?≈?15 and diastolic?≈?10 mmHg) and opioid withdrawal symptoms, and decreased opioid agonist symptoms and elated mood.

Conclusions

These findings concur with preclinical data by demonstrating that yohimbine increases drug seeking; in this study, these effects occurred without clinically significant subjective distress or elevated craving, and partly depended on opioid unit dose.     

On the behavioural specificity of hypophagia induced in male rats by mCPP,naltrexone, and their combination

Rationale

Serotonergic (5-hydroxytryptamine, 5-HT) and opioidergic mechanisms are intimately involved in appetite regulation.

Objectives

In view of recent evidence of positive anorectic interactions between opioid and various non-opioid substrates, our aim was to assess the behavioural specificity of anorectic responses to the opioid receptor antagonist naltrexone, the 5-HT_2C/1B receptor agonist mCPP and their combination.

Methods

Behavioural profiling techniques, including the behavioural satiety sequence (BSS), were used to examine acute drug effects in non-deprived male rats tested with palatable mash. Experiment 1 characterised the dose–response profile of mCPP (0.1–3.0 mg/kg), while experiment 2 assessed the effects of combined treatment with a sub-anorectic dose of mCPP (0.1 mg/kg) and one of two low doses of naltrexone (0.1 and 1.0 mg/kg).

Results

Experiment 1 confirmed the dose-dependent anorectic efficacy of mCPP, with robust effects on intake and feeding-related measures observed at 3.0 mg/kg. However, that dose was also associated with other behavioural alterations including increased grooming, reductions in locomotion and sniffing, and disruption of the BSS. In experiment 2, naltrexone dose-dependently reduced food intake and time spent feeding, effects accompanied by a behaviourally selective acceleration in the BSS. However, the addition of 0.1 mg/kg mCPP did not significantly alter the behavioural changes observed in response to either dose of naltrexone given alone.

Conclusions

In contrast to recently reported positive anorectic interactions involving low-dose combinations of opioid receptor antagonists or mCPP with cannabinoid CB1 receptor antagonists, present results would not appear to provide any support for potentially clinically relevant anorectic interactions between opioid and 5-HT_2C/1B receptor mechanisms.     

Dose-dependent sigma-1 receptor occupancy by donepezil in rat brain can be assessed with 11C-SA4503 and microPET

Rationale

Sigma-1 receptor agonists are under investigation as potential disease-modifying agents for several CNS disorders. Donepezil, an acetylcholinesterase inhibitor used for the symptomatic treatment of Alzheimer’s disease, is also a high-affinity sigma-1 agonist.

Objectives

The objectives of the present study were to investigate if the sigma-1 agonist tracer ¹¹C-SA4503 and microPET can be used to determine sigma-1 receptor occupancy (RO) of donepezil in the rat brain; to establish RO of donepezil at doses commonly used in rodent behavioural studies; and to determine the effective plasma concentration of donepezil required for 50 % of max-min occupancy (EC₅₀).

Methods

Male Wistar rats were pre-treated with donepezil (0.1 to 10 mg/kg) for about 1 h before microPET scans using ¹¹C-SA4503. The total distribution volume (V _T) of the tracer was determined by Logan graphical analysis using time activity curves from arterial plasma and regions of interest drawn around the entire brain and individual brain regions. RO by donepezil was calculated from a modified Lassen plot, and ED₅₀ was estimated from the sigmoidal dose-response curves obtained when the RO was plotted against log donepezil dose.

Results

A dose-dependent reduction was observed for V _T in the whole brain as well as individual brain regions. RO increased dose-dependently and was 93 % at 10 mg/kg. ED₅₀ was 1.29 mg/kg.

Conclusions

Donepezil, in the common dose range, was found to dose-dependently occupy a significant fraction of the sigma-1 receptor population. The data indicate that it is possible to determine sigma-1 RO by an agonist drug in rat brain, using ¹¹C-SA4503 and microPET.     

Pharmacokinetics,Tolerability, and Safety of the Single Oral Administration of AGSAV301 vs Exforge: A Randomized Crossover Study of Healthy Male Volunteers

Background and Objective

Valsartan, an angiotensin receptor blocker, is often used with calcium channel blockers (CCBs) such as amlodipine to control hypertension. Recently, the fixed-dose combination (FDC) of amlodipine 10 mg/valsartan 160 mg (Exforge) was approved. Amlodipine is a racemic mixture of CCB; S-amlodipine has higher activity than R-form. Therefore, AGSAV301, the FDC of S-amlodipine 5 mg/valsartan 160 mg was recently developed. The objective of this study was to compare the pharmacokinetic (PK) characteristics of S-amlodipine and valsartan when administered as one tablet each of Exforge and AGSAV301 to healthy male subjects.

Methods

This was a single-dose, randomized, open-label, two-way, two-period crossover study. Each subject received a single dose of AGSAV301 and Exforge, separated by a 3-week washout period. Plasma samples for the PK analysis of valsartan and S-amlodipine were collected at predose (0) and 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 16, 24, 36, 48, 72, 96, 120, and 168 h after administration. Tolerability was also evaluated.

Results

A total of 29 subjects were enrolled; 24 completed this study. The S-amlodipine maximum plasma concentration (C _max) geometric mean ratio (GMR) between AGSAV301 and Exforge was 0.951 (90 % CI 0.983–1.014), and area under the concentration–time curve from time 0 to last measured time point (AUC_last) was 0.917 (90 % CI 0.861–0.976). The GMR of valsartan C _max was 0.994 (90 % CI 0.918–1.076), and the AUC_last was 0.927 (90 % CI 0.821–1.047). All adverse events (AEs) were resolved without sequelae; no serious AEs were reported. Two drugs showed similar tendencies to lower blood pressure in healthy subjects.

Conclusions

The PK profiles of AGSAV301 and Exforge were bioequivalent. Both drugs were also well tolerated, with comparable AE profiles and similar blood pressure-lowering tendencies in healthy volunteers, suggesting equivalent therapeutic indications.     

Dopamine transporter availability in heroin-dependent subjects and controls: longitudinal changes during abstinence and the effects of Jitai tablets treatment

Rationale

Previous imaging studies have indicated that the levels of the dopamine transporter (DAT) are reduced in the brains of heroin users. However, whether these changes can be reversed by abstinence and/or treatment remains unclear.

Objectives

This study aims to investigate DAT availability in heroin users and changes in DAT availability after abstinence and treatment with the Jitai tablets, a traditional Chinese medicinal product that is approved for the treatment of opioid addiction.

Methods

Single-photon emission computed tomography (SPECT) with [^99mTc] TRODAT-1 was performed on heroin-dependent patients (n?=?64) and healthy controls (n?=?15). The patients were randomly assigned to treatment with either placebo or the Jitai. All patients underwent SPECT imaging both at baseline and after 6 months of treatment. DAT availability was assessed in the caudate and putamen. Depression and anxiety were evaluated at baseline.

Results

DAT availability remained at low levels during a 6-month period in the placebo-treated group but was increased (14–17 %) in the Jitai-treated group. The ratio of DAT availability at month 6 to that at baseline in the Jitai-treated group was significantly higher than that in the placebo-treated group in both the bilateral caudate and putamen. DAT uptake in the striatum was significantly correlated with daily heroin dose, years of heroin use, and depression.

Conclusions

These findings suggest that chronic heroin use induces long-lasting striatal DAT reductions. DAT availability remained unchanged during a 6-month period of abstinence. Treatment with Jitai appears to be effective at increasing striatal DAT availability.