Dose-dependent modulation of apoptotic processes by fluoxetine in maturing neuronal cells: an in vitro study
Ulrike Schaz1, Karl J Föhr, Stefan Liebau
1Institute of Anatomy and Cell Biology, University of Ulm, Ulm, Germany.
Objectives:
Recent studies indicate that the selective serotonin reuptake inhibitor (SSRI) fluoxetine is not solely effective by the instant inhibition of the serotonin transporter (SERT) but also by its influence on mitotic and/or apoptotic processes.
Methods:
To investigate the effects of the compound in vitro, we treated neurons from different brain areas with increasing concentrations of fluoxetine. Additionally, human embryonic kidney (HEK-293) cells and HEK-293 cells stably expressing the SERT were used. Cell viability was quantified by MTT-assay and apoptosis via fluorescence-activated cell-sorting analyses. Fluoxetine's effect on the γ-aminobutyric acid (GABA) receptor was electrophysiologically investigated to test the hypothesis if a GABA-mimetic effect exists that might lead - additionally to the well-known N-methyl-D-aspartate (NMDA)-antagonism - to increased apoptosis in immature neurons.
Results:
In hippocampal, cortical, and both types of HEK-293 cells, viability decreased and apoptosis increased in a dose-dependent manner (0.5-75 μM). In contrast, in mesencephalic and striatal cells the viability was unchanged or even slightly stimulated up to 20 μM fluoxetine. An anti-apoptotic effect of concentrations below 10 μM was observed in these cells. The GABA(A) receptor was directly activated by fluoxetine.
Conclusions:
We conclude that fluoxetine affects apoptotic processes independently from SERT expression. Since especially the combined GABA-mimetic and NMDA-antagonistic effects increase apoptosis in developing neuronal cells, whereas both effects are neuroprotective in adult neurons we hypothesise that these mechanisms explain the discrepancy of in vitro and in vivo studies.
Insights
Fluoxetine impacts cell death pathways beyond serotonin transporter inhibition. Its effects on apoptosis and GABA receptors differ between developing and adult neurons, potentially explaining varied study outcomes.
Area of Science:
- Neuroscience
- Pharmacology
- Cell Biology
Background:
- Selective serotonin reuptuptake inhibitors (SSRIs) like fluoxetine are primarily known for inhibiting the serotonin transporter (SERT).
- Emerging evidence suggests fluoxetine also influences cellular processes such as mitosis and apoptosis.
- Understanding these additional mechanisms is crucial for a comprehensive view of fluoxetine's action.
Purpose of the Study:
- To investigate the in vitro effects of fluoxetine on neuronal viability and apoptosis across different brain regions.
- To explore fluoxetine's interaction with the GABA(A) receptor and its potential GABA-mimetic effects.
- To determine if fluoxetine's impact on apoptosis is independent of SERT expression.
Main Methods:
- Neurons from various brain areas, HEK-293 cells, and SERT-expressing HEK-293 cells were treated with increasing fluoxetine concentrations.
- Cell viability was assessed using MTT assays, and apoptosis was quantified via fluorescence-activated cell sorting.
- Electrophysiological recordings were used to investigate fluoxetine's effect on the GABA(A) receptor.
Main Results:
- Fluoxetine decreased viability and increased apoptosis in hippocampal, cortical, and HEK-293 cells in a dose-dependent manner.
- Mesencephalic and striatal cells showed unchanged or stimulated viability up to 20 μM fluoxetine, with an anti-apoptotic effect below 10 μM.
- Fluoxetine directly activated the GABA(A) receptor.
Conclusions:
- Fluoxetine influences apoptotic processes independently of SERT expression.
- Combined GABA-mimetic and NMDA-antagonistic effects of fluoxetine increase apoptosis in developing neurons but are neuroprotective in adult neurons.
- These differential effects may explain discrepancies observed between in vitro and in vivo studies of fluoxetine.
