Antidepressant-induced undesirable weight gain: Prevention with rimonabant without interference with behavioral effectiveness

Targeting the Endocannabinoid CB1 Receptor to Treat Body Weight Disorders: A Preclinical and Clinical Review of the Therapeutic Potential of Past and Present CB1 Drugs

Obesity rates are increasing worldwide and there is a need for novel therapeutic treatment options. The endocannabinoid system has been linked to homeostatic processes, including metabolism, food intake, and the regulation of body weight. Rimonabant, an inverse agonist for the cannabinoid CB1 receptor, was effective at producing weight loss in obese subjects. However, due to adverse psychiatric side effects, rimonabant was removed from the market. More recently, we reported an inverse relationship between cannabis use and BMI, which has now been duplicated by several groups. As those results may appear contradictory, we review here preclinical and clinical studies that have studied the impact on body weight of various cannabinoid CB1 drugs. Notably, we will review the impact of CB1 inverse agonists, agonists, partial agonists, and neutral antagonists. Those findings clearly point out the cannabinoid CB1 as a potential effective target for the treatment of obesity. Recent preclinical studies suggest that ligands targeting the CB1 may retain the therapeutic potential of rimonabant without the negative side effect profile. Such approaches should be tested in clinical trials for validation.

Effect of Bioactive Phytochemicals from Phlomis viscosa Poiret on Wound Healing

Phlomis viscosa Poiret is an evergreen shrub growing in Israel, Turkey, Lebanon, and Syria with acknowledged pro-wound healing (WH) properties. In this study, we evaluated the pro-WH potential of selected compounds found in this plant. Among the pro-WH compounds (identified by us) was a combination of three chemicals-diosmin, 1-octen-3-ol, and himachala-2,4-diene which enhanced WH significantly both in in vitro and in vivo models. The determined phytochemicals combination could be used for the treatment of chronic wounds. The effect of the extracts, diosmin, 1-octen-3-ol on the secretion of pro-inflammatory cytokines, IL-6 (A) and IL-8 (B) by human dermal fibroblasts was significant (p < 0.001). In addition, the beneficial effect of extracts of P. viscosa and its phytochemicals on WH was evidenced by inhibiting the growth of several WH delaying microorganisms.

Cannabinoids in depressive disorders

Cannabis sativa is one of the most popular recreational and medicinal plants. Benefits from use of cannabinoid agents in epilepsy, multiple sclerosis, Parkinson's disease, Alzheimer's disease, and others have been suggested. It seems that the endocannabinoid system is also involved in the pathogenesis and treatment of depression, though its role in this mental disease has not been fully understood yet. Both the pro- and antidepressant activity have been reported after cannabis consumption and a number of pre-clinical studies have demonstrated that both agonist and antagonist of the endocannabinoid receptors act similarly to antidepressants. Responses to the cannabinoid agents are relatively fast, and most probably, the noradrenergic, serotoninergic, glutamatergic neurotransmission, neuroprotective activity, as well as modulation of the hypothalamic-pituitary-adrenal axis are implicated in the observed effects. Based on the published data, the endocannabinoid system evidently gives novel ideas and options in the field of antidepressant treatment, however further studies are needed to determine which group of patients could benefit from this type of therapy.

Care and feeding of the endocannabinoid system: a systematic review of potential clinical interventions that upregulate the endocannabinoid system

Background

The “classic” endocannabinoid (eCB) system includes the cannabinoid receptors CB₁ and CB₂, the eCB ligands anandamide (AEA) and 2-arachidonoylglycerol (2-AG), and their metabolic enzymes. An emerging literature documents the “eCB deficiency syndrome” as an etiology in migraine, fibromyalgia, irritable bowel syndrome, psychological disorders, and other conditions. We performed a systematic review of clinical interventions that enhance the eCB system—ways to upregulate cannabinoid receptors, increase ligand synthesis, or inhibit ligand degradation.

Methodology/Principal Findings

We searched PubMed for clinical trials, observational studies, and preclinical research. Data synthesis was qualitative. Exclusion criteria limited the results to 184 in vitro studies, 102 in vivo animal studies, and 36 human studies. Evidence indicates that several classes of pharmaceuticals upregulate the eCB system, including analgesics (acetaminophen, non-steroidal anti-inflammatory drugs, opioids, glucocorticoids), antidepressants, antipsychotics, anxiolytics, and anticonvulsants. Clinical interventions characterized as “complementary and alternative medicine” also upregulate the eCB system: massage and manipulation, acupuncture, dietary supplements, and herbal medicines. Lifestyle modification (diet, weight control, exercise, and the use of psychoactive substances—alcohol, tobacco, coffee, cannabis) also modulate the eCB system.

Conclusions/Significance

Few clinical trials have assessed interventions that upregulate the eCB system. Many preclinical studies point to other potential approaches; human trials are needed to explore these promising interventions.

Translational evidence for the involvement of the endocannabinoid system in stress-related psychiatric illnesses

Accumulating evidence over the past decade has highlighted an important role of the endocannabinoid (eCB) system in the regulation of stress and emotional behavior across divergent species, from rodents to humans. The general findings from this work indicate that the eCB system plays an important role in gating and buffering the stress response, dampening anxiety and regulating mood. Work in rodents has allowed researchers to determine the neural mechanisms mediating this relationship while work in human populations has demonstrated the possible importance of this system in stress-related psychiatric diseases, such as post-traumatic stress disorder, generalized anxiety and major depression. These stress-protective effects of eCB signaling appear to be primarily mediated by their actions within corticolimbic structures, particularly the amygdala and the prefrontal cortex. The aim of this review is to provide an up-to-date discussion of the current level of knowledge in this field, as well as address the current gaps in knowledge and specific areas of research that require attention.

Differential responses to distinct psychotropic agents of selectively bred dominant and submissive animals

Dominance and submissiveness are two opposite poles of behavior representing important functional elements in the development of social interactions. We previously demonstrated the inheritability of these traits by selective breeding based upon the dominant-submissive relationships (DSR) food competition paradigm. Continued multigenerational behavioral selection of Sabra mice yielded animal populations with strong and stable features of dominance and submissiveness. We found that these animals react differentially to stressogenic triggers, antidepressants and mood stabilizing agents. The anxiolytic compound diazepam (1.5mg/kg, i.p.) reduced anxiety-like behavior of submissive animals, but showed anxiogenic effects among dominant animals. In the Forced Swim test, the antidepressant paroxetine (1, 3 and 10mg/kg, i.p.) markedly reduced immobility of submissive animals, demonstrating antidepressant-like effect. In contrast, when administered to dominant animals, paroxetine caused extreme (frenetic) activity. The mood stabilizer lithium (0.4%, p.o.) selectively influenced dominant mice, without affecting the behavior of submissive animals. In summary, we describe here two distinct animal populations possessing strong dominant and submissive phenotypes. We suggest that these populations hold potential as tools for studying the molecular basis and pharmacogenetics of dominant and submissive behavior.

Desipramine inhibits histamine H1 receptor-induced Ca2+ signaling in rat hypothalamic cells

The hypothalamus in the brain is the main center for appetite control and integrates signals from adipose tissue and the gastrointestinal tract. Antidepressants are known to modulate the activities of hypothalamic neurons and affect food intake, but the cellular and molecular mechanisms by which antidepressants modulate hypothalamic function remain unclear. Here we have investigated how hypothalamic neurons respond to treatment with antidepressants, including desipramine and sibutramine. In primary cultured rat hypothalamic cells, desipramine markedly suppressed the elevation of intracellular Ca(2+) evoked by histamine H1 receptor activation. Desipramine also inhibited the histamine-induced Ca(2+) increase and the expression of corticotrophin-releasing hormone in hypothalamic GT1-1 cells. The effect of desipramine was not affected by pretreatment with prazosin or propranolol, excluding catecholamine reuptake activity of desipramine as an underlying mechanism. Sibutramine which is also an antidepressant but decreases food intake, had little effect on the histamine-induced Ca(2+) increase or AMP-activated protein kinase activity. Our results reveal that desipramine and sibutramine have different effects on histamine H1 receptor signaling in hypothalamic cells and suggest that distinct regulation of hypothalamic histamine signaling might underlie the differential regulation of food intake between antidepressants.

Putative role of endocannabinoid signaling in the etiology of depression and actions of antidepressants

In the last few years, there have been several advances in the determination of the role of the endocannabinoid system in the etiology of depression and the functional actions of antidepressant drugs. Specifically, a deficiency in endocannabinoid signaling is sufficient to produce a "depressive-like" phenotype at the preclinical level (including changes in rewarding, emotional and cognitive behavior and biological changes such as increased HPA axis activity, impaired stress adaptation, reduced neurogenesis and altered serotonin negative feedback), and capable of inducing symptoms of depression in humans at a clinical level. In line with these findings, clinical populations diagnosed with depression are found to have reduced levels of circulating endocannabinoids and preclinical models of depression reveal a deficit in central endocannabinoid signaling. Moreover, facilitation of endocannabinoid signaling is sufficient to produce all of the behavioral and biochemical effects of conventional antidepressant treatments. Further, many forms of antidepressant treatments significantly alter endocannabinoid signaling, and in some of these cases this recruitment of endocannabinoid signaling is involved in the neuroadaptive effects of these treatments. Ultimately, these data present a compelling picture of the putative role of the endocannabinoid system in the processes subserving both the development and treatment of depression.

Magnesium deficiency induces anxiety and HPA axis dysregulation: modulation by therapeutic drug treatment

Preclinical and some clinical studies suggest a relationship between perturbation in magnesium (Mg²⁺) homeostasis and pathological anxiety, although the underlying mechanisms remain largely unknown. Since there is evidence that Mg²⁺ modulates the hypothalamic-pituitary adrenal (HPA) axis, we tested whether enhanced anxiety-like behaviour can be reliably elicited by dietary Mg²⁺ deficiency and whether Mg²⁺ deficiency is associated with altered HPA axis function. Compared with controls, Mg²⁺ deficient mice did indeed display enhanced anxiety-related behaviour in a battery of established anxiety tests. The enhanced anxiety-related behaviour of Mg²⁺ deficient mice was sensitive to chronic desipramine treatment in the hyponeophagia test and to acute diazepam treatment in the open arm exposure test. Mg²⁺ deficiency caused an increase in the transcription of the corticotropin releasing hormone in the paraventricular hypothalamic nucleus (PVN), and elevated ACTH plasma levels, pointing to an enhanced set-point of the HPA axis. Chronic treatment with desipramine reversed the identified abnormalities of the stress axis. Functional mapping of neuronal activity using c-Fos revealed hyper-excitability in the PVN of anxious Mg²⁺ deficient mice and its normalisation through diazepam treatment. Overall, the present findings demonstrate the robustness and validity of the Mg²⁺ deficiency model as a mouse model of enhanced anxiety, showing sensitivity to treatment with anxiolytics and antidepressants. It is further suggested that dysregulations in the HPA axis may contribute to the hyper-emotionality in response to dietary induced hypomagnesaemia.

This article is part of a Special Issue entitled ‘Anxiety and Depression’.

Repeated immobilization stress increases nur77 expression in the bed nucleus of the stria terminalis

The transcription factor Nur77 has been identified as a neuronal activation marker of stressful stimuli in the central nervous system. Nur77 plays a key role at all levels of the hypothalamus-pituitary-adrenal axis during the stress response. However, the participation of Nur77 in extra-hypothalamic responses to stress is unknown. In this study, we studied the impact of acute and repeated immobilization stress on Nur77 expression in the bed nucleus of stria terminalis (BNST), a region involved in autonomic, neuroendocrine, and behavioral responses to stress. After a single session of immobilization stress we observed a significant increase of Nur77-like immunoreactivity in the BNST. This effect is not lost with repeated exposure to stress, since Nur77-like immunoreactivity and Nur77 mRNA in BNST were increased after the fifteenth stress session. The administration of desipramine, a specific inhibitor of noradrenaline reuptake, prevented the increase in Nur77-like immunoreactivity and mRNA induced by stress in rats subjected to repeated exposure to immobilization stress. Our results show that acute and repeated stress modulates Nur77 expression in BNST and suggest that Nur77 participates in extra-hypothalamic responses to stress.

Strain-specific outcomes of repeated social defeat and chronic fluoxetine treatment in the mouse

Social stress is a risk factor for affective disorders in vulnerable individuals. Although the biological nature of stress susceptibility/resilience remains to be elucidated, genetic variation is considered amongst the principal contributors to brain disorders. Furthermore, genetic predisposition may be determinant for the therapeutic outcome, as proposed for antidepressant treatments. In the present studies we compared the inherently diverse genetic backgrounds of 2 mouse strains by assessing the efficacy of a chronic antidepressant treatment in a repeated social stress procedure. C57BL/6J and BalbC mice underwent 10-day social defeats followed by 28-day fluoxetine treatment (10 mg/kg/mL, p.o.). In C57BL/6J, most of the social defeat-induced changes were of metabolic nature including persistently altered feed efficiency and decreased abdominal fat stores that were ameliorated by fluoxetine. BalbC mouse behavior was persistently affected by social defeat both in the social avoidance and the forced swim tests, and in either procedure it was restored by chronic fluoxetine, whereas their endocrine parameters were mostly unaffected. The highlighted strain-specific responsivity to the metabolic and behavioral consequences of social defeat and to the chronic antidepressant treatment offers a promising research tool to further explore the underlying neural mechanisms and genetic basis of stress susceptibility and treatment response.

Effects of Rhodiola rosea L. extract on behavioural and physiological alterations induced by chronic mild stress in female rats

Rhodiola rosea L. is one of the most popular adaptogen and an antistress plant in European and Asiatic traditional medicine. Our previous studies have confirmed the adaptogenic and antistress properties of a single administration of R. rosea L. extract in rats exposed to acute stress. There is increasing evidence that prolonged exposure to stressful life events and depression are both related to significant behavioural, endocrinological and neurobiological changes in human and animal subjects. The aim of this study was to determine whether chronic treatment with a hydroalcoholic R. rosea extract (RHO) standardized in 3% rosavin and 1% salidroside can prevent alterations induced in female rats following 6 weeks of a chronic mild stress (CMS) procedure. This was analysed through the behavioural and physiological parameters of consumption of 1% sucrose solution, locomotor and exploratory activities, body weight gain and oestrous cycle length. After the first 3 weeks of stress, RHO was administered daily by gavage at doses of 10, 15 and 20 mg/kg for the remaining 3 weeks. In addition, the antidepressant drug fluoxetine (10 mg/kg os), which has been shown to reverse CMS-induced disruptions, was used as the reference treatment. Rats subjected to the CMS procedure demonstrated decreased sucrose intake, reduced moving behaviour, minimized weight gain and dysregulation of their oestrous cycle. Treatment with RHO completely reverted all of these changes. The effects of RHO were comparable to those of fluoxetine. Interestingly, neither RHO nor fluoxetine influence the behavioural and physiological parameters tested in non-stressed animals. These findings strongly showed that chronic administration of RHO results in potent inhibition of the behavioural and physiological changes induced by chronic exposure to mild stressors.

Role of endocannabinoid signaling in anxiety and depression

Cannabinoid receptors and their endogenous ligands are located throughout the limbic, or "emotional," brain, where they modulate synaptic neurotransmission. Converging preclinical and clinical data suggest a role for endogenous cannabinoid signaling in the modulation of anxiety and depression. Augmentation of endocannabinoid signaling (ECS) has anxiolytic effects, whereas blockade or genetic deletion of CB₁ receptors has anxiogenic properties. Augmentation of ECS also appears to have anti-depressant actions, and in some assays blockade and genetic deletion of CB₁ receptors produces depressive phenotypes. These data provide evidence that ECS serves in an anxiolytic, and possibly anti-depressant, role. These data suggest novel approaches to treatment of affective disorders which could include enhancement of endogenous cannabinoid signaling, and warrant cautious use of CB₁ receptor antagonists in patients with pre-existing affective disorders.

Antidepressant-like behavioral effects of impaired cannabinoid receptor type 1 signaling coincide with exaggerated corticosterone secretion in mice

Hypothalamic-pituitary-adrenocortical (HPA) axis hyperactivity is associated with major depressive disorders, and treatment with classical antidepressants ameliorates not only psychopathological symptoms, but also the dysregulation of the HPA axis. Here, we further elucidated the role of impaired cannabinoid type 1 receptor (CB1) signaling for neuroendocrine and behavioral stress coping in the mouse forced swim test (FST). We demonstrate that the genetic inactivation of CB1 is accompanied by increased plasma corticosterone levels both under basal conditions and at different time points following exposure to the FST. The latter effect could be mimicked in C57BL/6N mice by acute, subchronic, and chronic administration of the selective CB1 antagonist SR141716. Further experiments confirmed the specificity of corticosterone-elevating SR141716 actions for CB1 in CB1-deficient mice. Subchronic and chronic pharmacological blockade of CB1, but not its genetic deletion, induced antidepressant-like behavioral responses in the FST that were characterized by decreased floating and/or increased struggling behavior. The antidepressant-like behavioral effects of acute desipramine treatment in the FST were absent in CB1-deficient mice, but the dampening effects of desipramine on FST stress-induced corticosterone secretion were not compromised by CB1 deficiency. However, antidepressant-like behavioral desipramine effects were intact in C57BL/6N mice pre-treated with SR141716, indicating potential developmental deficits in CB1-deficient mice. We conclude that pharmacological blockade of CB1 signaling shares antidepressant-like behavioral effects with desipramine, but reveals opposite effects on HPA axis activity.

A possible role for the endocannabinoid system in the neurobiology of depression

The present review synthetically describes the currently advanced hypotheses for a neurobiological basis of depression, ranging from the classical monoaminergic to the more recent neurotrophic hypothesis. Moreover, the Authors review the available preclinical and clinical evidence suggesting a possible role for the endocannabinoid system in the physiopathology of depression. Indeed, in spite of the reporting of conflicting results, the pharmacological enhancement of endocannabinoid activity at the CB1 cannabinoid receptor level appears to exert an antidepressant-like effect in some animal models of depression. On the contrary, a reduced activity of the endogenous cannabinoid system seems to be associated with the animal model of depression, namely the chronic mild stress model. Moreover, a few studies have reported an interaction of antidepressants with the endocannabinoid system. With regard to clinical studies, several authors have reported an alteration of endocannabinoid serum levels in depression, while post mortem studies have demonstrated increased levels of endocannabinoids associated to a concomitant hyperactivity of CB1 receptor in the prefrontal cortex of suicide victims. No clinical trials carried out using cannabinoids in the treatment of affective disorders have been published to date, although anecdotal reports have described both antidepressant and antimanic properties of cannabis as well as the ability of cannabis to induce mania that has also been documented. These findings are discussed, leading us to conclude that, although data available are sufficient to suggest a possible involvement of the endogenous cannabinoid system in the neurobiology of depression, additional studies should be performed in order to better elucidate the role of this system in the physiopathology of depression.

Impaired cannabinoid receptor type 1 signaling interferes with stress-coping behavior in mice

Dysregulation of the endocannabinoid system is known to interfere with emotional processing of stressful events. Here, we studied the role of cannabinoid receptor type 1 (CB1) signaling in stress-coping behaviors using the forced swim test (FST) with repeated exposures. We compared effects of genetic inactivation with pharmacological blockade of CB1 receptors both in male and female mice. In addition, we investigated potential interactions of the endocannabinoid system with monoaminergic and neurotrophin systems of the brain. Naive CB1 receptor-deficient mice (CB1-/-) showed increased passive stress-coping behaviors as compared to wild-type littermates (CB1+/+) in the FST, independent of sex. These findings were partially reproduced in C57BL/6N animals and fully reproduced in female CB1+/+ mice by pharmacological blockade of CB1 receptors with the CB1 receptor antagonist SR141716. The specificity of SR141716 was confirmed in female CB1-/- mice, where it failed to affect behavioral performance. Sensitivity to the antidepressants desipramine and paroxetine was preserved, but slightly altered in female CB1-/- mice. There were no genotype differences between CB1+/+ and CB1-/- mice in monoamine oxidase A and B activities under basal conditions, nor in monoamine content of hippocampal tissue after FST exposure. mRNA expression of vesicular glutamate transporter type 1 was unaffected in CB1-/- mice, but mRNA expression of brain-derived neurotrophic factor (BDNF) was reduced in the hippocampus. Our results suggest that impaired CB1 receptor function promotes passive stress-coping behavior, which, at least in part, might relate to alterations in BDNF function.