Alexandra Šulcová

Endocannabinoid system and mood disorders: priming a target for new therapies.

The endocannabinoid system (ECS), comprising two G protein-coupled receptors (the cannabinoid receptors 1 and 2 [CB1 and CB2] for marijuanas psychoactive principle ∆(9)-tetrahydrocannabinol [∆(9)-THC]), their endogenous small lipid ligands (namely anandamide [AEA] and 2-arachidonoylglycerol [2-AG], also known as endocannabinoids), and the proteins for endocannabinoid biosynthesis and degradation, has been suggested as a pro-homeostatic and pleiotropic signaling system activated in a time- and tissue-specific way during physiopathological conditions. In the brain activation of this system modulates the release of excitatory and inhibitory neurotransmitters and of cytokines from glial cells. As such, the ECS is strongly involved in neuropsychiatric disorders, particularly in affective disturbances such as anxiety and depression. It has been proposed that synthetic molecules that inhibit endocannabinoid degradation can exploit the selectivity of endocannabinoid action, thus activating cannabinoid receptors only in those tissues where there is perturbed endocannabinoid turnover due to the disorder, and avoiding the potential side effects of direct CB1 and CB2 activation. However, the realization that endocannabinoids, and AEA in particular, also act at other molecular targets, and that these mediators can be deactivated by redundant pathways, has recently led to question the efficacy of such approach, thus opening the way to new multi-target therapeutic strategies, and to the use of non-psychotropic cannabinoids, such as cannabidiol (CBD), which act via several parallel mechanisms, including indirect interactions with the ECS. The state of the art of the possible therapeutic use of endocannabinoid deactivation inhibitors and phytocannabinoids in mood disorders is discussed in this review article.

Inhibition of methamphetamine self-administration in rats by cannabinoid receptor antagonist AM 251.

Cannabinoids are drugs that are frequently abused not only alone, but also in combination with other drugs. The present study investigated possible functional interactions between the psychostimulant methamphetamine and the cannabinoid receptor agonists anandamide, or R-(+)-methanandamide and cannabinoid antagonist AM 251 in the rat model of i.v. drug self-administration. In rats trained to self-administer methamphetamine, the intake was significantly decreased by the cannabinoid antagonist and tended to be dose-dependently increased by pre-treatment with cannabinoid receptor agonists. Possible mechanisms for these drug interactions are discussed and the use of the cannabinoid antagonist for the treatment of drug abuse is considered.

Cannabinoids and Cytochrome P450 Interactions

OBJECTIVE This review consists of three parts, representing three different possibilities of interactions between cannabinoid receptor ligands of both exogenous and endogenous origin and cytochrome P450 enzymes (CYPs). The first part deals with cannabinoids as CYP substrates, the second summarizes current knowledge on the influence of various cannabinoids on the metabolic activity of CYP, and the third outline a possible involvement of the endocannabinoid system and cannabinoid ligands in the regulation of CYP liver activity. METHODS We performed a structured search of bibliographic and drug databases for peer-reviewed literature using focused review questions. RESULTS Biotransformation via a hydrolytic pathway is the major route of endocannabinoid metabolism and the deactivation of substrates is characteristic, in contrast to the minor oxidative pathway via CYP involved in the bioactivation reactions. Phytocannabinoids are extensively metabolized by CYPs. The enzymes CYP2C9, CYP2C19, and CYP3A4 catalyze most of their hydroxylations. Similarly, CYP represents a major metabolic pathway for both synthetic cannabinoids used therapeutically and drugs that are abused. In vitro experiments document the mostly CYP inhibitory activity of the major phytocannabinoids, with cannabidiol as the most potent inhibitor of many CYPs. The drug-drug interactions between cannabinoids and various drugs at the CYP level are reported, but their clinical relevance remains unclear. The direct activation/inhibition of nuclear receptors in the liver cells by cannabinoids may result in a change of CYP expression and activity. Finally, we hypothesize the interplay of central cannabinoid receptors with numerous nervous systems, resulting in a hormone-mediated signal towards nuclear receptors in hepatocytes.

Sex Differences in the Reinstatement of Methamphetamine Seeking after Forced Abstinence in Sprague-Dawley Rats

Preventing relapse to drug abuse is one of the struggles faced by clinicians in order to treat patients with substance use disorders (DSM-5). There is a large body of clinical evidence suggesting differential characteristics of the disorder in men and women, which is in line with preclinical findings as well. The aim of this study was to assess differences in relapse-like behavior in methamphetamine (METH) seeking after a period of forced abstinence, which simulates the real clinical situation very well. Findings from such study might add new insights in gender differences in relapse mechanisms to previous studies, which employ a classical drug or cue-induced reinstatement procedure following the extinction training. Adult male and female Sprague-Dawley rats were used in IV self-administration procedure conducted in operant boxes using nose-poke operandi (Coulborn Instruments, USA). Active nose-poke resulted in activation of the infusion pump to deliver one intravenous infusion of METH (0.08 mg/kg). After baseline drug intake was established (maintenance phase), a period of forced abstinence was initiated and rats were kept singly in their home cages for 14 days. Finally, one reinstatement session in operant boxes was conducted. Females were found to self-administer significantly lower dose of METH. The relapse rate was assessed as a number of active nose-pokes during the reinstatement session, expressed as a percentage of active nose-poking during the maintenance phase. Females displayed approximately 300% of active nose-pokes compared to 50% in males. This indicates higher vulnerability to relapse of METH seeking behavior in female rats. This effect was detected in all females, independently of current phase of their estrous cycle. Therefore, this paradigm using operant drug self-administration and reinstatement of drug-seeking after forced abstinence model can be used for preclinical screening for potential new anti-relapse medications specific for women.

Enhanced self-administration of the CB1 receptor agonist WIN55,212-2 in olfactory bulbectomized rats: evaluation of possible serotonergic and dopaminergic underlying mechanisms

Depression has been associated with drug consumption, including heavy or problematic cannabis use. According to an animal model of depression and substance use disorder comorbidity, we combined the olfactory bulbectomy (OBX) model of depression with intravenous drug self-administration procedure to verify whether depressive-like rats displayed altered voluntary intake of the CB1 receptor agonist WIN55,212-2 (WIN, 12.5 μg/kg/infusion). To this aim, olfactory-bulbectomized (OBX) and sham-operated (SHAM) Lister Hooded rats were allowed to self-administer WIN by lever-pressing under a continuous [fixed ratio 1 (FR-1)] schedule of reinforcement in 2 h daily sessions. Data showed that both OBX and SHAM rats developed stable WIN intake; yet, responses in OBX were constantly higher than in SHAM rats soon after the first week of training. In addition, OBX rats took significantly longer to extinguish the drug-seeking behavior after vehicle substitution. Acute pre-treatment with serotonin 5HT1B receptor agonist, CGS-12066B (2.5–10 mg/kg), did not significantly modify WIN intake in OBX and SHAM Lister Hooded rats. Furthermore, acute pre-treatment with CGS-12066B (10 and 15 mg/kg) did not alter responses in parallel groups of OBX and SHAM Sprague Dawley rats self-administering methamphetamine under higher (FR-2) reinforcement schedule with nose-poking as operandum. Finally, dopamine levels in the nucleus accumbens (NAc) of OBX rats did not increase in response to a WIN challenge, as in SHAM rats, indicating a dopaminergic dysfunction in bulbectomized rats. Altogether, our findings suggest that a depressive-like state may alter cannabinoid CB1 receptor agonist-induced brain reward function and that a dopaminergic rather than a 5-HT1B mechanism is likely to underlie enhanced WIN self-administration in OBX rats.

Felbamate reduces hormone release and locomotor hypoactivity induced by repeated stress of social defeat in mice

Glutamatergic neurotransmission plays a role in stress hormone release and the development of mood diseases. The aim of these studies was to verify the hypothesis that repeated treatment with felbamate, an antiepileptic drug modulating glutamatergic neurotransmission, affects hormone release in response to chronic stress. A mouse model of repeated social defeat (nonaggressive male mouse repeatedly defeated by aggressive counterparts) was used. The results showed that acute treatment with felbamate reduced hypolocomotion in an open field induced by repeated social conflict. The same stress procedure resulted in increased release of corticosterone and dopamine. Felbamate decreased noradrenaline concentrations and inhibited stress-induced rise in corticosterone and dopamine. It is suggested that modulation of stress hormone release may be induced by the action of felbamate on glutamate neurotransmission, and neuroendocrine changes could contribute to behavioural effects of the drug. Antidepressant action of this mood-stabilizing drug suggested by clinicians needs further verification.

The effects of methamphetamine self-administration on behavioural sensitization in the olfactory bulbectomy rat model of depression

Depression is frequently comorbid with a drug addiction and may seriously complicate its treatment. Currently, there is no routinely used animal model to investigate this comorbidity. In this study the effect of repeated administration of methamphetamine on i.v. drug self-administration in an olfactory bulbectomy model of depression in rats was investigated in order to propose and validate a rat model of comorbid depression and addiction. Male Wistar rats were either olfactory-bulbectomized (OBX) or sham-operated. They subsequently underwent a methamphetamine sensitization regime, which consisted of daily i.p. injections of methamphetamine for a 14-d period; controls received Sal injections at the same frequency. The i.v. self-administration of methamphetamine (0.08 mg/kg in one infusion) paradigm on a fixed ratio schedule of reinforcement was performed using operant chambers. A significant decrease of the drug intake was recorded in sham-operated animals pretreated with methamphetamine when compared to the unpretreated group. This was not apparent in the OBX groups. Both groups of OBX animals exhibited a higher intake of methamphetamine compared to the corresponding sham-operated groups, thus confirming the hypothesis of higher drug intake in depressive conditions in this rodent model. The procedure of behavioural sensitization to methamphetamine decreased the number of self-administered drug doses per session in the sham-operated rats. It is hypothesized that this phenomenon resulted from increasing efficacy of the drug after behavioural sensitization caused by repeated methamphetamine intermittent administration.

Serum dextromethorphan/dextrorphan metabolic ratio for CYP2D6 phenotyping in clinical practice

What is known and Objective:  Accurate prediction of actual CYP2D6 metabolic activity may prevent some adverse drug reactions and improve therapeutic response in patients receiving CYP2D6 substrates. Dextromethorphan‐to‐dextrorphan metabolic ratio (MRDEM/DOR) is well established as a marker of CYP2D6 metabolizer status. The relationship between urine and plasma or serum MRDEM/DOR is not well established nor is there evidence of antimode for separation of intermediate and especially poor metabolizers (PM) from extensive metabolizers (EM). This study addressed whether CYP2D6 phenotyping using molar metabolic ratio of dextromethorphan to dextrorphan (MRDEM/DOR) in serum is usable and reliable in clinical practice as urinary MRDEM/DOR.

Tiagabine Treatment is Associated with Neurochemical, Immune and Behavioural Alterations in the Olfactory Bulbectomized Rat Model of Depression

INTRODUCTION Affective disorders are often associated with immune and neuroendocrine disturbances. However, little information on the modulatory effects of antiepileptics on endocrine and immune functions is available. Some novel antiepileptics, including tiagabine, are considered as potential antidepressants. METHODS We investigated the influence of tiagabine on stress hormone release, cellular immune function and behaviour in rats following olfactory bulbectomy (OB), a well-recognized animal model of depression. RESULTS Hyperlocomotion in the open field, typical for the OB rodents, was attenuated by repeated treatment with tiagabine (12 mg/kg/day) in a similar fashion to standard antidepressants. OB led to significantly decreased lymphocyte and increased neutrophil counts, and suppressed leukocyte phagocytosis. The OB-induced changes in leukocyte differential counts were not found in the tiagabine-treated group. The OB-induced reduction in plasma noradrenaline levels was normalized following tiagabine treatment. DISCUSSION The present data bring further evidence on the antidepressant-like action of tiagabine and encourage further research on its use in the treatment of affective disorders. The observed changes in immune and endocrine functions may contribute to its mood stabilizing effect.

Effect of methamphetamine on cytochrome P450 activity.

Amphetamine-based drugs, including methamphetamine, are some of the most widely used illegal drugs in the world. Methamphetamine is metabolized by the cytochrome P450s, the latter also being involved in the metabolism of many drugs and other xenobiotics. The effect of methamphetamine pretreatment (10 mg kg–1, intraperitoneally once daily for 6 days) on the activity of the P450 enzymes was assessed both in the rat isolated perfused liver and in vivo. The rate of 4-hydroxydiclofenac production was significantly enhanced in vivo, indicating a possible stimulatory effect on P4502C6. Similarly, the kinetics of tolbutamide and dextromethorphan in isolated perfused rat liver indicate a significant increase in both P4502C6 and the P4502D subfamily. No significant changes in midazolam kinetic in the isolated perfused rat liver were observed. The potential for methamphetamine to cause drug interactions is of clinical relevance and, therefore, it warrants further investigation. Until further drug interaction experiments are accomplished, the co-administration of drugs with methamphetamine should be conducted with caution.