Five potential therapeutic agents as antidepressants: a brief review and future directions

Exploring the potential anti-thyroid activity of Acetyl-L-carnitine: Lactoperoxidase inhibition profile, iodine complexation and scavenging power against H2O2. Experimental and theoretical studies

L-Acetylcarnitine (ALC), a versatile compound, has demonstrated beneficial effects in depression, Alzheimer's disease, cognitive impairment, and other conditions. This study focuses on its antithyroid activity. The precursor molecule, L-carnitine, inhibited the uptake of triiodothyronine (T3) and thyroxine (T4), and it is possible that ALC may reduce the iodination process of T3 and T4. Currently, antithyroid drugs are used to control the excessive production of thyroid hormones (TH) through various mechanisms: (i) forming electron donor-acceptor complexes with molecular iodine, (ii) eliminating hydrogen peroxide, and (iii) inhibiting the enzyme thyroid peroxidase. To understand the pharmacological properties of ALC, we investigated its plausible mechanisms of action. ALC demonstrated the ability to capture iodine (Kc = 8.07 ± 0.32 x 105 M-1), inhibit the enzyme lactoperoxidase (LPO) (IC50 = 17.60 ± 0.76 µM), and scavenge H2O2 (39.82 ± 0.67 mM). A comprehensive physicochemical characterization of ALC was performed using FTIR, Raman, and UV-Vis spectroscopy, along with theoretical DFT calculations. The inhibition process was assessed through fluorescence spectroscopy and vibrational analysis. Docking and molecular dynamics simulations were carried out to predict the binding mode of ALC to LPO and to gain a better understanding into the inhibition process. Furthermore, albumin binding experiments were also conducted. These findings highlight the potential of ALC as a therapeutic agent, providing valuable insights for further investigating its role in the treatment of thyroid disorders.

Drug Design Targeting the Muscarinic Receptors and the Implications in Central Nervous System Disorders

There is substantial evidence that cholinergic system function impairment plays a significant role in many central nervous system (CNS) disorders. During the past three decades, muscarinic receptors (mAChRs) have been implicated in various pathologies and have been prominent targets of drug-design efforts. However, due to the high sequence homology of the orthosteric binding site, many drug candidates resulted in limited clinical success. Although several advances in treating peripheral pathologies have been achieved, targeting CNS pathologies remains challenging for researchers. Nevertheless, significant progress has been made in recent years to develop functionally selective orthosteric and allosteric ligands targeting the mAChRs with limited side effect profiles. This review highlights past efforts and focuses on recent advances in drug design targeting these receptors for Alzheimer’s disease (AD), schizophrenia (SZ), and depression.

Novel Antimuscarinic Antidepressant-like Compounds with Reduced Effects on Cognition

The cholinergic nervous system has been implicated in mood disorders, evident in the fast-onset antidepressant effects of scopolamine, a potent muscarinic antagonist, in clinical studies. One prominent disadvantage of the use of scopolamine in the treatment of depression is its detrimental effects on cognition, especially as such effects might aggravate cognitive deficits that occur with depression itself. Thus, the identification of antimuscarinic drugs that are free of such detrimental effects may provide an important avenue for the development of novel therapeutics for the management of depression. The present data in rats indicate that a historical muscarinic antagonist, L-687,306, and a muscarinic antagonist of our own design, CJ2100, were as or more effective than scopolamine in antagonizing both the bradycardic effects of the muscarinic agonist arecoline in cardiovascular studies and its discriminative stimulus and rate-decreasing effects in behavioral studies. Additionally, both novel muscarinic antagonists were as effective as scopolamine in decreasing immobility in the forced swim test, a preclinical indicator of potential antidepressant activity. However, at equieffective or even larger doses, they were considerably less disruptive than scopolamine in assays of cognition-related behavior. All three drugs displayed high specificity for the mAChRs with few off-target binding sites, and CJ2100 showed modest affinity across the mAChRs when compared with L-687,306 and scopolamine. These data emphasize the dissimilar pharmacological profiles that are evident across antimuscarinic compounds and the potential utility of novel antagonists for the improved treatment of depression. SIGNIFICANCE STATEMENT: Some clinical studies with the muscarinic antagonist scopolamine document its ability to produce antidepressant effects in patients with mood disorders; however, scopolamine also has well known adverse effects on both autonomic and centrally mediated physiological functions that limit its therapeutic use. This study characterizes the cardiovascular and discriminative stimulus effects of two novel muscarinic antagonists, L-687,306 and CJ2100, that produce antidepressant-like effects in a rodent model (forced swim test) without affecting touchscreen-based cognitive performance (titrating psychomotor vigilance and delayed matching-to-position).

Rapid Onset of Intranasal Esketamine in Patients with Treatment Resistant Depression and Major Depression with Suicide Ideation: A Meta-Analysis

Objective

We performed a meta-analysis of randomized double-blinded placebo controlled trials (DB-RCTs) to investigate efficacy and safety of intranasal esketamine in treating major depressive disorder (MDD) including treatment resistant depression (TRD) and major depression with suicide ideation (MDSI).

Methods

Mean change in total scores on Montgomery-Åsberg Depression Rating Scale (MADRS) from baseline to different time-points were our primary outcome measure. Secondary efficacy measures included rate of remission of depression and resolution of suicidality.

Results

Eight DB-RCTs (seven published and one un-published) covering 1,488 patients with MDD were included. Esketamine more significantly improved MADRS total scores than placebo starting from 2-4 hours after the first administration (standardized mean difference, -0.41 [95% CI, -0.58 to -0.25], p < 0.00001), and this superiority maintained until end of double-blinded period (28 days). Sub-group analysis showed that superior antidepressant effects of esketamine over placebo in TRD and MDSI was observed from 2-4 hours, which was maintained until 28 days. Resolution of suicide in MDSI was also greater for esketamine than for placebo at 2-4 hours (OR of 2.04, 95% CIs, 1.37 to 3.05, p = 0.0005), but two groups did not statistically differ at 24 hours and day 28. Total adverse events (AEs), and other common AEs including dissociation, blood pressure increment, nausea, vertigo, dysgeusia, dizziness, and somnolence were more frequent in esketamine than in placebo group.

Conclusion

Esketamine showed rapid antidepressant effects in patients with MDD, including TRD and MDSI. The study also suggested that esketamine might be associated with rapid anti-suicidal effects for patients with MDSI.

Protein kinase A mediates scopolamine-induced mTOR activation and an antidepressant response

BACKGROUND

Clinical reports have shown that scopolamine produces a rapid (3-4 d) and potent anti-depressive response without severe adverse effects. Animal experiments have proven that scopolamine induces mTOR pathway activation in an AMPAR dependent manner. The present study aimed to determine the role of PKA in scopolamine-induced potentiation of AMPAR, as well as in mTOR pathway activation and rapid antidepressant effects.

METHODS

We utilized electrophysiological recording, Western blotting, and behavior tests to examine the effects of scopolamine, the selective M2 cholinergic receptor antagonist methoctramine, and H89, a PKA specific inhibitor on AMPAR potentiation, mTOR pathway activation, and behavioral responses in a rat depression model of learned helplessness.

RESULTS

Scopolamine (1μM) rapidly increased AMPAR-fEPSP amplitudes and membrane GluA1 expression in CA1 region of hippocampal slices, both of which were abolished by H89. Moreover, scopolamine promoted AMPAR phosphorylation on GluA1 ser845, a PKA site involved in GluA1 membrane insertion. H89 disrupted both GluA1 ser845 phosphorylation and mTOR activation, as well as the antidepressant effects of scopolamine as determined via forced swim test. Additionally, methoctramine mimicked the effects of scopolamine on phosphorylation and counter-depressive action in a PKA-dependent manner.

LIMITATIONS

Only one test was used to evaluate depressive behavior, and gene knock-out rats were not yet utilized to refine our hypotheses.

CONCLUSION

Our findings revealed that PKA pathway is necessary for scopolamine-induced synaptic plasticity and mTOR pathway activation, and indicated that a potential M2-PKA mechanism underlies scopolamine's antidepressant effects. Such findings suggest that GluA1 ser845 phosphorylation may be a trigger event for scopolamine's actions, and that PKA may represent a novel target for the treatment of depressive symptoms.

Vilazodone for the Treatment of Depression: An Update

Vilazodone is a novel antidepressant having a selective serotonin (5-HT) reuptake inhibitor and 5-HT1A receptor partial agonist profile, so it has been regarded as a serotonin partial agonist-reuptake inhibitor (SPARI). We aimed to provide Vilazodone's clinical implications mainly by reviewing published clinical trials. Vilazodone has been speculated to have three potential benefits including faster onset of action, greater efficacy, and better tolerability owning to its SPARI properties. However, no studies conducted so far have directly proven the above speculations. Five initial phase II trials failed to distinguish vilazodone from placebo in the treatment of MDD, but 4 randomized clinical trials (RCT), 3 post-hoc or pooled analysis, 1 long-term open label study, and a meta-analysis showed vilazodone's superior efficacy over placebo. The studies also showed vilazodone is generally safe and tolerable. However, diarrhea, nausea, headache, dizziness, dry mouth, and insomnia warrant close attention in clinical practice because they have been constantly noted throughout the clinical studies. 2 RCTs recently documented the efficacy and safety of vilazodone in patients with generalized anxiety disorder, which could be a start of broadening vilazodone's usage or FDA approval in diverse anxiety disorders.