Involvement of muscarinic receptor mechanisms in antidepressant drug action.

Conventional antidepressants typically require weeks of daily dosing to achieve full antidepressant response in antidepressant responders. A newly evolving group of compounds can engender more rapid response times in depressed patients. These drugs include the newly approved antidepressant (S)-ketamine (esketamine, Spravato). A seminal study by Furey and Drevets in 2006 showed antidepressant response in patients after only a few doses with the antimuscarinic drug scopolamine. Several clinical reports have generally confirmed scopolamine as a rapid-acting antidepressant. The data with scopolamine are consistent with the adrenergic/cholinergic hypothesis of mania/depression derived from clinical reports originating in the 1970s from Janowsky and colleagues. Additional support for a role for muscarinic receptors in mood disorders comes from the greater efficacy of conventional antidepressants that have relatively high levels of muscarinic receptor blocking actions (e.g., the tricyclic antidepressant amitriptyline vs the selective serotonin reuptake inhibitor fluoxetine). There appears to be appreciable overlap in the mechanisms of action of scopolamine and other rapid-acting antidepressants (ketamine) or putative rapid-acting agents (mGlu2/3 receptor antagonists) although gaps exist in the experimental literature. Current hypotheses regarding the mechanisms underlying the rapid antidepressant response to scopolamine posit an M1 receptor subtype-initiated cascade of biological events that involve the amplification of AMPA receptors. Consequent impact on brain-derived neurotrophic factor and mTor signaling pathways result in the induction of dendritic spines that enable augmented functional connectivity in brain areas regulating mood. Two major goals for research in this area focus on finding ways in which scopolamine might best be utilized for depressed patients and the discovery of alternative compounds that improve upon the efficacy and safety of scopolamine.

Rapid-acting antidepressants.

Conventional antidepressants (biogenic amine mechanisms) are not fully efficacious (e.g., symptoms remain after treatment, not all patients respond), produce effects only after weeks of daily dosing, and do not impact all disease symptoms. In contrast, a new class of antidepressants has been emerging since 2006 that has demonstrated rapid onset, large effect size, activity after only a single or few dose applications, and positive impact in treatment refractory patients and against some treatment-resistant symptoms (e.g., anhedonia). Rapid-acting antidepressant drug action has been demonstrated in controlled clinical studies for ketamine, a few other NMDA receptor antagonists, and scopolamine. Less clinical data are currently available for psychedelic drugs such as psilocybin, lysergic acid diethylamide, and ayahuasca. The mechanisms of action of rapid-acting antidepressants are not fully understood. However, a general triggering mechanism appears to involve the potentiation of AMPA receptor function. Although the durability of antidepressant effects of ketamine and scopolamine is limited, psychedelic drugs have been reported to produce effects for many months. The primary impediment to generating a medicine of this type for depressed patients is side effects and the lack of methods to ensure enduring antidepressant effects. Thus, further exploration of drug possibilities continues. Esketamine ((S)-ketamine) was recently FDA approved. Compounds currently in clinical development include the NMDA receptor antagonist (R)-ketamine, the NMDA receptor modulator, GLYX-13 (Rapastinel), and the AMPA receptor potentiator TAK-653. Additional pharmacological classes have produced effects in the preclinical laboratory to suggest their potential as rapid-acting agents. These include mGlu2/3 receptor antagonists, AMPA receptor potentiators, and negative allosteric modulators of GABAA(α5) receptors. In all cases, molecules exist that could be used to provide clinical proof of concept testing.

Further Evaluation of Mechanisms Associated with the Antidepressantlike Signature of Scopolamine in Mice.

BACKGROUND: Conventional antidepressants lack efficacy for many patients (treatmentresistant depression or TRD) and generally take weeks to produce full therapeutic response in others. Emerging data has identified certain drugs such as ketamine as rapidly-acting antidepressants for major depressive disorder and TRD. Scopolamine, a drug used to treat motion sickness and nausea, has also been demonstrated to function as a rapidly-acting antidepressant. The mechanisms associated with efficacy in TRD patients and rapid onset of action have been suggested to involve a-Amino-3-hydroxy- 5-methyl-4-isoxazolepropionic acid (AMPA) receptor and mammalian target of rapamycin (mTOR) signaling. Since the work on these mechanisms with scopolamine has been limited, the present set of experiments was designed to further explore these mechanisms of action. METHOD: Male, NIH Swiss mice demonstrated a robust and immediate antidepressant signature with ketamine or scopolamine when studied under the forced-swim test. RESULTS: The AMPA receptor antagonist NBQX prevented this antidepressant-like effect of scopolamine and ketamine. An orally-bioavilable mTOR inhibitor (AZD8055) also attenuated the antidepressant- like effects of scopolamine and ketamine. Scopolamine was also shown to augment the antidepressant- like effect of the selective serotonin reuptake inhibitor citalopram. When given in combination, scopolamine and ketamine acted synergistically to produce antidepressant-like effects. Although drug interaction data suggested that additional mechanisms might be at play, metabolomic analysis of frontal cortex and plasma from muscarinic M1+/+ and M1 -/- mice given scopolamine or vehicle did not reveal any hints as to the nature of these additional mechanisms of action. CONCLUSION: Overall, the data substantiate and extend the idea that AMPA and mTOR signaling pathways are necessary for the antidepressant-like effects of scopolamine and ketamine, mechanisms that appear to be of general significance for TRD therapeutic agents.

Efficacy in patients with dry eye after treatment with a new lubricant eye drop formulation.

PURPOSE: The effective management of dry eye must include a clinically meaningful reduction in ocular staining. Evaluations of corneal and conjunctival staining and other ocular symptoms of dry eye were conducted for a new formulation of polyethylene glycol 400/propylene glycol-based lubricant eye drops containing hydroxypropyl guar as a gelling agent (Test Product) in comparison to Optive Lubricant Eye Drops (Control Product) in adult patients with dry eye. METHODS: One hundred thirteen patients, 18 years of age and older, with dry eye were enrolled in a prospective, double-masked, multisite, parallel-group study. After a 2-week run-in period during which patients administered aqueous saline eye drops 4 times daily (QID) in each eye, patients were randomized (1:1) to receive either Test Product or Control Product to be administered QID for 6 weeks. Efficacy and safety were evaluated by corneal and conjunctival staining scores, tear film breakup time, assessments of ocular symptoms, ocular surface disease index (OSDI) scores, dry eye treatment satisfaction, visual function-14 questionnaires, and adverse events. RESULTS: The intent-to-treat data set included 105 patients randomized to Test Product (n = 52) or Control Product (n = 53). Patients primarily were between the ages of 18-64 years (70.5%), female (73.3%), white (93.3%), and not Hispanic (81.9%). Patients in the Test Product group exhibited significantly lower mean corneal staining scores than the Control Product group at day 14 (P = 0.0009) and day 42 (P = 0.0106), and significantly lower mean conjunctival staining scores at day 28 (P = 0.0475) and day 42 (P = 0.0009). Patients in both treatment groups reported significant reductions in the mean scores for the ocular symptoms of dryness, gritty/sandy feeling, and burning (P