Efficacy and safety of scopolamine compared to placebo in individuals with bipolar disorder who are experiencing a depressive episode (SCOPE-BD): study protocol for a randomised double-blind placebo-controlled trial

Review of traditional uses, phytochemistry and pharmacology of Tibetan Medicine tangchong

ETHNOPHARMACOLOGICAL RELEVANCE

Tangchong (ཐང་ཕྲོམ།), a term in the Tibetan language, encompasses a diverse group of plants belonging to different genera of the Solanaceae family. These plants have been utilized in traditional Tibetan medicine for centuries and are currently still employed to treat a variety of ailments, including acute and severe abdominal pain, intestinal obstruction, epilepsy, ascariasis, lung abscess, and other diseases. The therapeutic properties of tangchong are attributed to the presence of tropane alkaloids (TAs), although recent research has also revealed their toxicity.

AIM OF THIS REVIEW

The purpose of this review is to provide a comprehensive analysis of the traditional uses of tangchong, as well as the phytochemical and pharmacological studies conducted on this plant. The review aims to offer a critical update on the current state of knowledge of tangchong and to identify new opportunities for exploring its therapeutic potential.

MATERIALS AND METHODS

To gather information on tangchong, we conducted a thorough search of several scientific databases, including Google Scholar, Web of Science, Scifinder, Baidu Scholar, PubMed, and CNKI.

RESULTS

This review summarizes the traditional usage of 11 plants, 168 chemical components, including alkaloids, flavonoids, steroids, amides, coumarins, etc., describes the pharmacological activities of these medicinal plants and their mechanisms of action, provides an elaboration of toxicology, and provides new plant-derived drugs and herbal preparations from tangchong.

CONCLUSIONS

Clarity regarding the source of the drug is crucial to ensure the safety and efficacy of clinical applications of Tibetan medicine. In this paper, we provide a comprehensive review of tangchong, including its traditional medicinal uses, chemical composition, pharmacology, toxicology, and quality control measures. Our analysis highlights the significant value of tangchong as an ethnomedicinal resource, with pharmacological activities primarily linked to its alkaloid content. Furthermore, this review serves as a valuable reference for future research on alkaloid-containing ethnomedicines.

The Potential of Scopolamine as an Antidepressant in Major Depressive Disorder: A Systematic Review of Randomized Controlled Trials

Major depressive disorder is one of the most severe mental disorders. It strongly impairs daily functioning, and, in extreme cases, it can lead to suicide. Although different treatment options are available for patients with depression, there is an ongoing search for novel therapeutic agents, such as scopolamine (also known as hyoscine), that would offer higher efficacy, a more rapid onset of action, and a more favorable safety profile. The aim of our study was to review the current clinical evidence regarding the use of scopolamine, a promising therapeutic option in the treatment of depression. A systematic literature search was performed using PubMed, Embase, and CENTRAL databases up to 5 June 2023. We included randomized placebo-controlled or head-to-head clinical trials that compared the clinical efficacy and safety of scopolamine in the treatment of major depressive disorder. Two reviewers independently conducted the search and study selection and rated the risk of bias for each study. Four randomized controlled trials were identified in the systematic review. The included studies investigated the use of scopolamine administered as an oral, intramuscular, or intravenous drug, alone or in combination with other antidepressants. The results indicated that scopolamine exerts antidepressant effects of varying intensity. We show that not all studies confirmed a statistically and clinically significant reduction of depressive symptoms vs. placebo. A broader perspective on scopolamine use in antidepressant treatment should be confirmed in subsequent large randomized controlled trials assessing both effectiveness and safety. Therefore, studies directly comparing the effectiveness of scopolamine depending on the route of administration are required.

Rapid-acting antidepressants targeting modulation of the glutamatergic system: clinical and preclinical evidence and mechanisms

Major depressive disorder (MDD) is a devastating mental illness that affects approximately 20% of the world's population. It is a major disease that leads to disability and suicide, causing a severe burden among communities. Currently available medications for treating MDD target the monoaminergic systems. The most prescribed medications include selective serotonin reuptake inhibitors and selective norepinephrine reuptake inhibitors. However, these medications have serious drawbacks, such as a delayed onset requiring weeks or months to reach efficacy and drug resistance, as one-third of patients are unresponsive to the medications. Therefore, it is imperative to develop novel therapies with rapid action, high efficacy and few adverse effects. The discovery of the rapid antidepressant effect of ketamine has triggered tremendous enthusiasm for studying new antidepressants that target the glutamatergic system in the central nervous system. Many agents that directly or indirectly modulate the glutamatergic system have been shown to provide rapid and lasting antidepressant action. Among these agents, ketamine, an antagonist of metabotropic glutamate 2/3 receptors, and scopolamine, an unspecific muscarinic acetylcholine receptor antagonist, have been extensively studied. In this review, we discuss the clinical and preclinical evidence supporting the antidepressant efficacy of these agents and the current understanding of the underlying mechanisms.

Rapid antidepressant-like effects of muscarinic receptor antagonists require BDNF-dependent signaling in the ventrolateral periaqueductal gray

RATIONALE

Clinical reports reveal that scopolamine, an acetylcholine muscarinic receptor antagonist, exerts rapid antidepressant effects in depressed patients, but the mechanisms underlying the therapeutic effects have not been fully identified.

OBJECTIVES

The present study examines the cellular mechanisms by which scopolamine produces antidepressant-like effects through its action in the ventrolateral midbrain periaqueductal gray (vlPAG).

METHODS

We used a well-established mouse model of depression induced by chronic restraint stress (CRS) exposure for 14 days. Behaviors were tested using the forced swim test (FST), tail suspension test (TST), female urine sniffing test (FUST), novelty-suppressed feeding test (NSFT), and locomotor activity (LMA). Synaptic transmission in the vlPAG was measured by whole-cell patch-clamp recordings. IntravlPAG microinjection was used to pharmacologically verify the signaling cascades of scopolamine in the vlPAG.

RESULTS

The results demonstrated that intraperitoneal injection of scopolamine produced antidepressant-like effects in a dose-dependent manner without affecting locomotor activity. CRS elicited depression-like behaviors, whereas intraperitoneal injection of scopolamine alleviated CRS-induced depression-like behaviors. CRS diminished glutamatergic transmission in the vlPAG, while scopolamine reversed the above effects. Moreover, intravlPAG microinjection of the L-type voltage-dependent calcium channel (VDCC) blocker verapamil, tropomyosin-related kinase B (TrkB) receptor antagonist ANA-12, mammalian target of rapamycin complex 1 (mTORC1) inhibitor rapamycin, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA) antagonist CNQX prevented scopolamine-induced antidepressant-like effects.

CONCLUSIONS

Scopolamine ameliorated CRS-elicited depression-like behavior required activation of VDCC, resulting in activity-dependent release of brain-derived neurotrophic factor (BDNF), engaging the TrkB receptor and downstream mTORC1 signaling in the vlPAG.