Comparison of Caffeine and d-amphetamine in Cocaine-Dependent Subjects: Differential Outcomes on Subjective and Cardiovascular Effects, Reward Learning, and Salivary Paraxanthine

Pharmacokinetics of Caffeine: A Systematic Analysis of Reported Data for Application in Metabolic Phenotyping and Liver Function Testing

Caffeine is by far the most ubiquitous psychostimulant worldwide found in tea, coffee, cocoa, energy drinks, and many other beverages and food. Caffeine is almost exclusively metabolized in the liver by the cytochrome P-450 enzyme system to the main product paraxanthine and the additional products theobromine and theophylline. Besides its stimulating properties, two important applications of caffeine are metabolic phenotyping of cytochrome P450 1A2 (CYP1A2) and liver function testing. An open challenge in this context is to identify underlying causes of the large inter-individual variability in caffeine pharmacokinetics. Data is urgently needed to understand and quantify confounding factors such as lifestyle (e.g., smoking), the effects of drug-caffeine interactions (e.g., medication metabolized via CYP1A2), and the effect of disease. Here we report the first integrative and systematic analysis of data on caffeine pharmacokinetics from 141 publications and provide a comprehensive high-quality data set on the pharmacokinetics of caffeine, caffeine metabolites, and their metabolic ratios in human adults. The data set is enriched by meta-data on the characteristics of studied patient cohorts and subjects (e.g., age, body weight, smoking status, health status), the applied interventions (e.g., dosing, substance, route of application), measured pharmacokinetic time-courses, and pharmacokinetic parameters (e.g., clearance, half-life, area under the curve). We demonstrate via multiple applications how the data set can be used to solidify existing knowledge and gain new insights relevant for metabolic phenotyping and liver function testing based on caffeine. Specifically, we analyzed 1) the alteration of caffeine pharmacokinetics with smoking and use of oral contraceptives; 2) drug-drug interactions with caffeine as possible confounding factors of caffeine pharmacokinetics or source of adverse effects; 3) alteration of caffeine pharmacokinetics in disease; and 4) the applicability of caffeine as a salivary test substance by comparison of plasma and saliva data. In conclusion, our data set and analyses provide important resources which could enable more accurate caffeine-based metabolic phenotyping and liver function testing.

Cardiac autonomic functioning across stress and reward: Links with depression in emerging adults

The autonomic nervous system (ANS) has received much attention as a potential low-cost, peripheral indicator of depression. Despite theoretical support, however, results have been mixed as to whether indices of the ANS reliably index depression. In response, the present study sought to clarify the relation between ANS activity and depression by examining cardiac autonomic balance (CAB) and cardiac autonomic regulation (CAR), two composite indices of the parasympathetic and sympathetic nervous system, within both a stressful and rewarding context. We hypothesized that CAB_Stress, representing the difference between the parasympathetic and sympathetic branches in response to stress, and CAR_Reward, representing the summation of the two branches in response to reward, will be most indicative of depressogenic risk. We examined the parasympathetic (i.e., respiratory sinus arrhythmia) and sympathetic (i.e., pre-ejection period) responses of 97 emerging adults (M_age = 18.93) for a stress (i.e., negative mood induction) and reward (i.e., probabilistic learning) task, as well as their depressive symptoms at baseline, 3-week, and 6-week follow-up. Analyses found partial support for our hypotheses, revealing greater CAR_Reward (i.e., coactivation of both branches) was related to lower depressive symptoms. Further, exploratory analyses examining gender differences found lower CAB_Stress (i.e., sympathetically-oriented response) was predictive of an increasing trajectory of depression, but only among males. Overall, the current study highlights the importance of simultaneously examining both branches of the ANS across various environmental contexts. Research and clinical implications of the current findings are discussed.

Pharmacotherapeutic strategies for treating cocaine use disorder-what do we have to offer?

BACKGROUND

Cocaine use contines to be a significant public health problem world-wide. However, despite substantial research efforts, no pharmacotherapies are approved for the treatment of cocaine use disorder (CUD).

ARGUMENT

Studies have identified positive signals for a range of medications for treating CUD. These include long-acting amphetamine formulations, modafinil, topiramate, doxazosin and combined topiramate and mixed amphetamine salts extended-release (MAS-ER). However, valid conclusions about a medication's clinical efficacy require nuanced approaches that take into account behavioural phenotypes of the target population (frequency of use, co-abuse of cocaine and other substances, genetic subgroups, psychiatric comorbidity), variables related to the medication (dose, short-/long-acting formulations, titration speed, medication adherence) and other factors that may affect treatment outcomes. Meta-analyses frequently do not account for these co-varying factors, which contributes to a somewhat nihilistic view on pharmacotherapeutic options for CUD. In addition, the predominant focus on abstinence, which is difficult for most patients to achieve, may overshadow more nuanced therapeutic signals.

CONCLUSION

While there is an emphasis on finding new medications with novel mechanisms of action for treating CUD, currently available medications deserve further investigation based on the existing literature. Evaluating refined metrics of treatment success in well-defined subgroups of patients, and further exploring combination therapies and their synergy with behavioural/psychosocial interventions, are promising avenues to establishing effective therapies for CUD.

The Role of Adenosine Receptors in Psychostimulant Addiction

Adenosine receptors (AR) are a family of G-protein coupled receptors, comprised of four members, named A1, A2A, A2B, and A3 receptors, found widely distributed in almost all human body tissues and organs. To date, they are known to participate in a large variety of physiopathological responses, which include vasodilation, pain, and inflammation. In particular, in the central nervous system (CNS), adenosine acts as a neuromodulator, exerting different functions depending on the type of AR and consequent cellular signaling involved. In terms of molecular pathways and second messengers involved, A1 and A3 receptors inhibit adenylyl cyclase (AC), through Gi/o proteins, while A2A and A2B receptors stimulate it through Gs proteins. In the CNS, A1 receptors are widely distributed in the cortex, hippocampus, and cerebellum, A2A receptors are localized mainly in the striatum and olfactory bulb, while A2B and A3 receptors are found at low levels of expression. In addition, AR are able to form heteromers, both among themselves (e.g., A1/A2A), as well as with other subtypes (e.g., A2A/D2), opening a whole range of possibilities in the field of the pharmacology of AR. Nowadays, we know that adenosine, by acting on adenosine A1 and A2A receptors, is known to antagonistically modulate dopaminergic neurotransmission and therefore reward systems, being A1 receptors colocalized in heteromeric complexes with D1 receptors, and A2A receptors with D2 receptors. This review documents the present state of knowledge of the contribution of AR, particularly A1 and A2A, to psychostimulants-mediated effects, including locomotor activity, discrimination, seeking and reward, and discuss their therapeutic relevance to psychostimulant addiction. Studies presented in this review reinforce the potential of A1 agonists as an effective strategy to counteract psychostimulant-induced effects. Furthermore, different experimental data support the hypothesis that A2A/D2 heterodimers are partly responsible for the psychomotor and reinforcing effects of psychostimulant drugs, such as cocaine and amphetamine, and the stimulation of A2A receptor is proposed as a potential therapeutic target for the treatment of drug addiction. The overall analysis of presented data provide evidence that excitatory modulation of A1 and A2A receptors constitute promising tools to counteract psychostimulants addiction.

Differential sensitivity to learning from positive and negative outcomes in cocaine users

BACKGROUND

Altered sensitivity to positive and negative outcomes may be linked to the maladaptive choices characteristic of substance use disorders. Few studies have determined the distinct roles that positive and negative outcomes play in stimulus-response learning in cocaine users. The purpose of the present study was to investigate sensitivity to learning from positive and negative outcomes on a probabilistic learning task in cocaine users employing human laboratory and crowdsourcing techniques.

METHODS

Individuals who reported cocaine use were recruited for a laboratory study (Experiment 1) or an online study on Amazon.com's Mechanical Turk (mTurk) (Experiment 2). All participants completed a feedback-based probabilistic learning task in which images were classified into categories (A versus B). Positive and negative outcomes were provided in a probabilistic manner on separate trials. Proportion of optimal responses and response times were recorded.

RESULTS

Active cocaine users were less sensitive to learning from positive relative to negative outcomes. These effects were consistent across image type and session in the laboratory sample. Similarly, reduced sensitivity to learning from positive outcomes was observed in cocaine users on mTurk. Control participants did not show suboptimal performance following positive or negative outcomes.

CONCLUSIONS

This study extends the limited research on feedback-based learning in drug users by demonstrating reduced sensitivity to positive outcomes in cocaine users recruited in the human laboratory and online. Future studies on the clinical significance and mechanisms underlying this bias are needed to understand its relevance as a target for intervention development.

Measuring the subjective: revisiting the psychometric properties of three rating scales that assess the acute effects of hallucinogens

OBJECTIVE

In the present study we explored the psychometric properties of three widely used questionnaires to assess the subjective effects of hallucinogens: the Hallucinogen Rating Scale (HRS), the Mystical Experience Questionnaire (MEQ), and the Addiction Research Center Inventory (ARCI).

METHODS

These three questionnaires were administered to a sample of 158 subjects (100 men) after taking ayahuasca, a hallucinogen whose main active component is N,N-dimethyltryptamine (DMT). A confirmatory factorial study was conducted to check the adjustment of previous data obtained via theoretical proposals. When this was not possible, we used an exploratory factor analysis without restrictions, based on tetrachoric and polychoric matrices and correlations.

RESULTS

Our results sparsely match the theoretical proposals of the authors, perhaps because previous studies have not always employed psychometric methods appropriate to the data obtained. However, these data should be considered preliminary, pending larger samples to confirm or reject the proposed structures obtained.

CONCLUSIONS

It is crucial that instruments of sufficiently precise measurement are utilized to make sense of the information obtained in the study of the subjective effects of psychedelic drugs. Copyright © 2016 John Wiley & Sons, Ltd.

The effects of oral d-amphetamine on impulsivity in smoked and intranasal cocaine users

BACKGROUND

Effective treatments for cocaine use disorders remain elusive. Two factors that may be related to treatment failures are route of cocaine used and impulsivity. Smoked cocaine users are more likely to have poorer treatment outcomes compared to intranasal cocaine users. Further, cocaine users are impulsive and impulsivity is associated with poor treatment outcomes. While stimulants are used to treat Attention Deficit Hyperactivity Disorder (ADHD) and attenuate certain cocaine-related behaviors, few studies have comprehensively examined whether stimulants can reduce behavioral impulsivity in cocaine users, and none examined route of cocaine use as a factor.

METHODS

The effects of immediate release oral d-amphetamine (AMPH) were examined in 34 cocaine users (13 intranasal, 21 smoked). Participants had three separate sessions where they were administered AMPH (0, 10, or 20mg) and completed behavioral measures of impulsivity and risk-taking and subjective measures of abuse liability.

RESULTS

Smoked cocaine users were more impulsive on the Delayed Memory Task, the GoStop task and the Delay Discounting Task than intranasal cocaine users. Smoked cocaine users also reported more cocaine craving and negative mood than intranasal cocaine users. AMPH produced minimal increases on measures of abuse liability (e.g., Drug Liking).

CONCLUSIONS

Smoked cocaine users were more impulsive than intranasal cocaine users on measures of impulsivity that had a delay component. Additionally, although AMPH failed to attenuate impulsive responding, there was minimal evidence of abuse liability in cocaine users. These preliminary findings need to be confirmed in larger samples that control for route and duration of cocaine use.