Abstract

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This study investigates the developmental neurotoxicity (DNT) of paroxetine—a widely prescribed SSRI—using BrainSpheres, a 3D human brain model derived from induced pluripotent stem cells (iPSCs). While current animal-based DNT testing is costly and poorly predictive of human outcomes, BrainSpheres offer a more relevant in vitro platform for assessing synaptogenesis, neurite outgrowth, and myelination. Exposure to therapeutic blood concentrations of paroxetine (20–60 ng/ml) resulted in significant reductions in synaptic marker expression, neurite complexity, and oligodendrocyte populations without causing cytotoxicity. These findings underscore paroxetine’s potential developmental neurotoxicity and support broader adoption of human-relevant models like BrainSpheres in preclinical drug safety testing.

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Key Learnings

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• Paroxetine exposure at therapeuticlevels impairs key neurodevelopmental processes including synaptogenesis,neurite outgrowth, and oligodendrocyte development.

• No general cytotoxicity ormitochondrial dysfunction was observed, suggesting targeted neurodevelopmentalimpact.

• 3D BrainSpheres models enablemultimodal assessments—including molecular, cellular, and morphologicalendpoints—in a single platform.

• Differences in sensitivity across iPSClines highlight the potential for modeling individual variability in drugresponse.

• Findings support rethinking the safetyof SSRI use during later stages of pregnancy and bolster the case foralternatives to animal testing.

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Methods

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Model: BrainSpheres derived from two independent human iPSC lines.

Exposure: Continuous treatment with 0, 20, or 60 ng/ml paroxetine over 8 weeks.

Assays Conducted:

• Cell viability (resazurin assay)
• Mitochondrial function (MitoTracker)
• Immunohistochemistry for neuronal andglial markers
• Synaptic protein expression (SYP,PSD95) via western blot and confocal microscopy
• Neurite outgrowth quantified usingSholl analysis
• Oligodendrocyte quantification usingO4 staining and myelination pixel overlap

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Conclusions

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Paroxetine exposure during neurodevelopment disrupts multiple critical processes—despite the absence of general cytotoxic effects—indicating that therapeutic concentrations may pose neurodevelopmental risks. These data align with concerns raised by epidemiological and animal studies. The 3D BrainSpheres model successfully replicates synaptogenesis, neurite development, and early myelination, making it a powerful and ethically superior tool for DNT screening. The findings emphasize the importance of reevaluating SSRI use in pregnancy and adopting human-relevant, high-content platforms for safety assessment of neuroactive compounds.

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Reference

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Zhong X, Harris G, Smirnova L, Zufferey V, Sá RCS, Baldino Russo F, et al. Antidepressant paroxetine exerts developmental neurotoxicity in an iPSC-derived 3D human brain model. Front Cell Neurosci. 2020;14:25. doi:10.3389/fncel.2020.00025