Effects of Escitalopram on Endoplasmic Reticulum Stress and Oxidative Stress Induced by Tunicamycin

Sertraline modulates hippocampal plasticity and learning via sigma 1 receptors, cellular stress and neurosteroids

In addition to modulating serotonin transport, selective serotonin reuptake inhibitors (SSRIs) have multiple other effects that may contribute to clinical effects, and some of these latter actions prompt repurposing of SSRIs for non-psychiatric indications. We recently observed that the SSRIs fluvoxamine and fluoxetine prevent the acute adverse effects of pro-inflammatory stimulation on long-term potentiation (LTP) in the CA1 hippocampal region. Sertraline showed markedly different effects, acutely inhibiting LTP at a low micromolar concentration through inverse agonism of sigma 1 receptors (S1Rs). In the present studies, we pursued mechanisms contributing to sertraline modulation of LTP in rat hippocampal slices. We found that sertraline partially inhibits synaptic responses mediated by N-methyl-D-aspartate receptors (NMDARs) via effects on NMDARs that express GluN2B subunits. A selective S1R antagonist (NE-100), but not an S1R agonist (PRE-084) blocked effects on NMDARs, despite the fact that both S1R ligands were previously shown to prevent LTP inhibition. Both NE-100 and PRE-084, however, prevented adverse effects of sertraline on one-trial learning. Because of the important role that S1Rs play in modulating endoplasmic reticulum stress, we examined whether inhibitors of cellular stress alter effects of sertraline. We found that two stress inhibitors, ISRIB and quercetin, prevented LTP inhibition, as did inhibitors of the synthesis of endogenous neurosteroids, which are homeostatic regulators of cellular stress. These studies highlight complex effects of sertraline, S1Rs and neurosteroids on hippocampal function and have relevance for understanding therapeutic and adverse drug actions.

Mitochondrial oxidative stress in brain microvascular endothelial cells: Triggering blood-brain barrier disruption

Blood-brain barrier disruption plays an important role in central nervous system diseases. This review provides information on the role of mitochondrial oxidative stress in brain microvascular endothelial cells in cellular dysfunction, the disruption of intercellular junctions, transporter dysfunction, abnormal angiogenesis, neurovascular decoupling, and the involvement and aggravation of vascular inflammation and illustrates related molecular mechanisms. In addition, recent drug and nondrug therapies targeting cerebral vascular endothelial cell mitochondria to repair the blood-brain barrier are discussed. This review shows that mitochondrial oxidative stress disorder in brain microvascular endothelial cells plays a key role in the occurrence and development of blood-brain barrier damage and may be critical in various pathological mechanisms of blood-brain barrier damage. These new findings suggest a potential new strategy for the treatment of central nervous system diseases through mitochondrial modulation of cerebral vascular endothelial cells.

SSRIs differentially modulate the effects of pro-inflammatory stimulation on hippocampal plasticity and memory via sigma 1 receptors and neurosteroids

Certain selective serotonin reuptake inhibitors (SSRIs) have anti-inflammatory effects in preclinical models, and recent clinical studies suggest that fluvoxamine can prevent deterioration in patients with COVID-19, possibly through activating sigma 1 receptors (S1Rs). Here we examined potential mechanisms contributing to these effects of fluvoxamine and other SSRIs using a well-characterized model of pro-inflammatory stress in rat hippocampal slices. When hippocampal slices are exposed acutely to lipopolysaccharide (LPS), a strong pro-inflammatory stimulus, basal synaptic transmission in the CA1 region remains intact, but induction of long-term potentiation (LTP), a form of synaptic plasticity thought to contribute to learning and memory, is completely disrupted. Administration of low micromolar concentrations of fluvoxamine and fluoxetine prior to and during LPS administration overcame this LTP inhibition. Effects of fluvoxamine required both activation of S1Rs and local synthesis of 5-alpha reduced neurosteroids. In contrast, the effects of fluoxetine did not involve S1Rs but required neurosteroid production. The ability of fluvoxamine to modulate LTP and neurosteroid production was mimicked by a selective S1R agonist. Additionally, fluvoxamine and fluoxetine prevented learning impairments induced by LPS in vivo. Sertraline differed from the other SSRIs in blocking LTP in control slices likely via S1R inverse agonism. These results provide strong support for the hypothesis that S1Rs and neurosteroids play key roles in the anti-inflammatory effects of certain SSRIs and that these SSRIs could be beneficial in disorders involving inflammatory stress including psychiatric and neurodegenerative illnesses.

The Importance of Endoplasmic Reticulum Stress as a Novel Antidepressant Drug Target and Its Potential Impact on CNS Disorders

Many central nervous system (CNS) diseases, including major depressive disorder (MDD), are underpinned by the unfolded protein response (UPR) activated under endoplasmic reticulum (ER) stress. New, more efficient, therapeutic options for MDD are needed to avoid adverse effects and drug resistance. Therefore, the aim of the work was to determine whether UPR signalling pathway activation in astrocytes may serve as a novel target for antidepressant drugs. Among the tested antidepressants (escitalopram, amitriptyline, S-ketamine and R-ketamine), only S-ketamine, and to a lesser extent R-ketamine, induced the expression of most ER stress-responsive genes in astrocytes. Furthermore, cell viability and apoptosis measuring assays showed that (R-)S-ketamine did not affect cell survival under ER stress. Under normal conditions, S-ketamine played the key role in increasing the release of brain-derived neurotrophic factor (BDNF), indicating that the drug has a complex mechanism of action in astrocytes, which may contribute to its therapeutic effects. Our findings are the first to shed light on the relationship between old astrocyte specifically induced substance (OASIS) stabilized by ER stress and (R-)S-ketamine; however, the possible involvement of OASIS in the mechanism of therapeutic ketamine action requires further study.