Differential effects of fluoxetine and venlafaxine in the neural embryonic stem cell test (ESTn) revealed by a cell lineage map

Transcriptomic characterization of 2D and 3D human induced pluripotent stem cell-based in vitro models as New Approach Methodologies for developmental neurotoxicity testing

The safety and developmental neurotoxicity (DNT) potential of chemicals remain critically understudied due to limitations of current in vivo testing guidelines, which are low throughput, resource-intensive, and hindered by species differences that limit their relevance to human health. To address these issues, robust New Approach Methodologies (NAMs) using deeply characterized cell models are essential. This study presents the comprehensive transcriptomic characterization of two advanced human-induced pluripotent stem cell (hiPSC)-derived models: a 2D adherent and a 3D neurosphere model of human neural progenitor cells (hiNPCs) differentiated up to 21 days. Using high-throughput RNA sequencing, we compared gene expression profiles of 2D and 3D models at three developmental stages (3, 14, and 21 days of differentiation). Both models exhibit maturation towards post-mitotic neurons, with the 3D model maturing faster and showing a higher prevalence of GABAergic neurons, while the 2D model is enriched with glutamatergic neurons. Both models demonstrate broad applicability domains, including excitatory and inhibitory neurons, astrocytes, and key endocrine and especially the understudied cholinergic receptors. Comparison with human fetal brain samples confirms their physiological relevance. This study provides novel in-depth applicability insights into the temporal and dimensional aspects of hiPSC-derived neural models for DNT testing. The complementary use of these two models is highlighted: the 2D model excels in synaptogenesis assessment, while the 3D model is particularly suited for neural network formation as observed as well in previous functional studies with these models. This research marks a significant advancement in developing human-relevant, high-throughput DNT assays for regulatory purposes.

Modeling extrahepatic hepatitis E virus infection in induced human primary neurons

Hepatitis E virus (HEV) infections are one of the most common causes of acute viral hepatitis, annually causing over 3 million symptomatic cases and 70,000 deaths worldwide. Historically, HEV was described as a hepatotropic virus, but has recently been associated with various extrahepatic manifestations including neurological disorders such as Guillain-Barré syndrome and neuralgic amyotrophy. However, the underlying pathogenesis of these neurological diseases remains largely unknown. The aim of this study was to investigate extrahepatic HEV manifestations in a neuronal model system using human-induced primary neurons (iPNs). Renal epithelial cells from human urine were reprogrammed to induced pluripotent stem cells to generate neuronal progenitor cells, which were subsequently differentiated into iPNs over 21 d. These iPNs supported HEV infection preferentially in neurite-bearing cells. Transcriptional profiling of the neuronal development process as well as viral infection dynamics in iPNs uncovered a lack of antiviral innate immune responses to HEV infection with only an intrinsic expression of distinct interferon-regulated genes and signaling molecules. Viral open reading frame 2 encoded capsid protein could be visualized by volumetric three-dimensional reconstitution within the neurites, which were reduced in length in an HEV inoculation-dependent manner. In conclusion, this neuron-derived human model system provides a powerful tool for studying extrahepatic manifestations of HEV infection. It further indicates a potential mechanism of pathogenesis driven by the interaction between host and viral factors.

Assessing the Neurodevelopmental Impact of Fluoxetine, Citalopram, and Paroxetine on Neural Stem Cell-Derived Neurons

BACKGROUND/OBJECTIVES

Many pregnant women globally suffer from depression and are routinely prescribed selective serotonin reuptake inhibitors (SSRIs). These drugs function by blocking the re-uptake of serotonin by the serotonin transporter (SERT) into neurons, resulting in its accumulation in the presynaptic cleft. Despite a large amount of research suggesting a potential link to neurodevelopmental disorders in children whose mothers took these drugs during pregnancy, their possible adverse effects are still debated, and results are contradictory. On the other hand, there is an immediate need for improved cell-based models for developmental neurotoxicity studies (DNT) to minimize the use of animals in research.

METHODS

In this study, we aimed to assess the effects of clinically relevant concentrations of paroxetine (PAR), fluoxetine (FLX), and citalopram (CIT)-on maturing neurons derived from human neural stem cells using multiple endpoints.

RESULTS

Although none of the tested concentrations of FLX, CIT, or PAR significantly affected cell viability, FLX (10 µM) exhibited the highest reduction in viability compared to the other drugs. Regarding neurite outgrowth, CIT did not have a significant effect. However, FLX (10 µM) significantly reduced both mean neurite outgrowth and mean processes, PAR significantly reduced mean processes, and showed a trend of dysregulation of multiple genes associated with neuronal development at therapeutic-relevant serum concentrations.

CONCLUSIONS

Transcriptomic data and uptake experiments found no SERT activity in the system, suggesting that the adverse effects of FLX and PAR are independent of SERT.

Screening autism-associated environmental factors in differentiating human neural progenitors with fractional factorial design-based transcriptomics

Research continues to identify genetic variation, environmental exposures, and their mixtures underlying different diseases and conditions. There is a need for screening methods to understand the molecular outcomes of such factors. Here, we investigate a highly efficient and multiplexable, fractional factorial experimental design (FFED) to study six environmental factors (lead, valproic acid, bisphenol A, ethanol, fluoxetine hydrochloride and zinc deficiency) and four human induced pluripotent stem cell line derived differentiating human neural progenitors. We showcase the FFED coupled with RNA-sequencing to identify the effects of low-grade exposures to these environmental factors and analyse the results in the context of autism spectrum disorder (ASD). We performed this after 5-day exposures on differentiating human neural progenitors accompanied by a layered analytical approach and detected several convergent and divergent, gene and pathway level responses. We revealed significant upregulation of pathways related to synaptic function and lipid metabolism following lead and fluoxetine exposure, respectively. Moreover, fluoxetine exposure elevated several fatty acids when validated using mass spectrometry-based metabolomics. Our study demonstrates that the FFED can be used for multiplexed transcriptomic analyses to detect relevant pathway-level changes in human neural development caused by low-grade environmental risk factors. Future studies will require multiple cell lines with different genetic backgrounds for characterising the effects of environmental exposures in ASD.

Cure of Alzheimer's Dementia Requires Addressing All of the Affected Brain Cell Types

Multiple genetic, metabolic, and environmental abnormalities are known to contribute to the pathogenesis of Alzheimer's dementia (AD). If all of those abnormalities were addressed it should be possible to reverse the dementia; however, that would require a suffocating volume of drugs. Nevertheless, the problem may be simplified by using available data to address, instead, the brain cells whose functions become changed as a result of the abnormalities, because at least eleven drugs are available from which to formulate a rational therapy to correct those changes. The affected brain cell types are astrocytes, oligodendrocytes, neurons, endothelial cells/pericytes, and microglia. The available drugs include clemastine, dantrolene, erythropoietin, fingolimod, fluoxetine, lithium, memantine, minocycline, pioglitazone, piracetam, and riluzole. This article describes the ways by which the individual cell types contribute to AD's pathogenesis and how each of the drugs corrects the changes in the cell types. All five of the cell types may be involved in the pathogenesis of AD; of the 11 drugs, fingolimod, fluoxetine, lithium, memantine, and pioglitazone, each address all five of the cell types. Fingolimod only slightly addresses endothelial cells, and memantine is the weakest of the remaining four. Low doses of either two or three drugs are suggested in order to minimize the likelihood of toxicity and drug-drug interactions (including drugs used for co-morbidities). Suggested two-drug combinations are pioglitazone plus lithium and pioglitazone plus fluoxetine; a three-drug combination could add either clemastine or memantine. Clinical trials are required to validate that the suggest combinations may reverse AD.

Supplementary Pharmacotherapy for the Behavioral Abnormalities Caused by Stressors in Humans, Focused on Post-Traumatic Stress Disorder (PTSD)

Used as a supplement to psychotherapy, pharmacotherapy that addresses all of the known metabolic and genetic contributions to the pathogenesis of psychiatric conditions caused by stressors would require an inordinate number of drugs. Far simpler is to address the abnormalities caused by those metabolic and genetic changes in the cell types of the brain that mediate the behavioral abnormality. Relevant data regarding the changed brain cell types are described in this article and are derived from subjects with the paradigmatic behavioral abnormality of PTSD and from subjects with traumatic brain injury or chronic traumatic encephalopathy. If this analysis is correct, then therapy is required that benefits all of the affected brain cell types; those are astrocytes, oligodendrocytes, synapses and neurons, endothelial cells, and microglia (the pro-inflammatory (M1) subtype requires switching to the anti-inflammatory (M2) subtype). Combinations are advocated using several drugs, erythropoietin, fluoxetine, lithium, and pioglitazone, that benefit all of the five cell types, and that should be used to form a two-drug combination, suggested as pioglitazone with either fluoxetine or lithium. Clemastine, fingolimod, and memantine benefit four of the cell types, and one chosen from those could be added to the two-drug combination to form a three-drug combination. Using low doses of chosen drugs will limit both toxicity and drug-drug interactions. A clinical trial is required to validate both the advocated concept and the choice of drugs.

Formulating treatment of major psychiatric disorders: algorithm targets the dominantly affected brain cell-types

BACKGROUND

Pharmacotherapy for most psychiatric conditions was developed from serendipitous observations of benefit from drugs prescribed for different reasons. An algorithmic approach to formulating pharmacotherapy is proposed, based upon which combination of changed activities by brain cell-types is dominant for any particular condition, because those cell-types contain and surrogate for genetic, metabolic and environmental information, that has affected their function. The algorithm performs because functions of some or all the affected cell-types benefit from several available drugs: clemastine, dantrolene, erythropoietin, fingolimod, fluoxetine, lithium, memantine, minocycline, pioglitazone, piracetam, and riluzole PROCEDURES/FINDINGS: Bipolar disorder, major depressive disorder, schizophrenia, Alzheimer's disease, and post-traumatic stress disorder, illustrate the algorithm; for them, literature reviews show that no single combination of altered cell-types accounts for all cases; but they identify, for each condition, which combination occurs most frequently, i.e., dominates, as compared with other possible combinations. Knowing the dominant combination of altered cell-types in a particular condition, permits formulation of therapy with combinations of drugs taken from the above list. The percentage of patients who might benefit from that therapy, depends upon the frequency with which the dominant combination occurs in patients with that particular condition.

CONCLUSIONS

Knowing the dominant combination of changed cell types in psychiatric conditions, permits an algorithmically formulated, rationally-based treatment. Different studies of the same condition often produce discrepant results; all might be correct, because identical clinical phenotypes result from different combinations of impaired cell-types, thus producing different results. Clinical trials would validate both the proposed concept and choice of drugs.

Neuronal differentiation pathways and compound-induced developmental neurotoxicity in the human neural progenitor cell test (hNPT) revealed by RNA-seq

There is an increased awareness that the use of animals for compound-induced developmental neurotoxicity (DNT) testing has limitations. Animal-free innovations, especially the ones based on human stem cell-based models are pivotal in studying DNT since they can mimic processes relevant to human brain development. Here we present the human neural progenitor test (hNPT), a 10-day protocol in which neural progenitor cells differentiate into a neuron-astrocyte co-culture. The study aimed to characterise differentiation over time and to find neurodevelopmental processes sensitive to compound exposure using transcriptomics. 3992 genes regulated in unexposed control cultures (p ≤ 0.001, log2FC ≥ 1) showed Gene Ontology (GO-) term enrichment for neuronal and glial differentiation, neurite extension, synaptogenesis, and synaptic transmission. Exposure to known or suspected DNT compounds (acrylamide, chlorpyrifos, fluoxetine, methyl mercury, or valproic acid) at concentrations resulting in 95% cell viability each regulated unique combinations of GO-terms relating to neural progenitor proliferation, neuronal and glial differentiation, axon development, synaptogenesis, synaptic transmission, and apoptosis. Investigation of the GO-terms 'neuron apoptotic process' and 'axon development' revealed common genes that were responsive across compounds, and might be used as biomarkers for DNT. The GO-term 'synaptic signalling', on the contrary, whilst also responsive to all compounds tested, showed little overlap in gene expression regulation patterns between the conditions. This GO-term may articulate compound-specific effects that may be relevant for revealing differences in mechanism of toxicity. Given its focus on neural progenitor cell to mature multilineage neuronal cell maturation and its detailed molecular readout based on gene expression analysis, hNPT might have added value as a tool for neurodevelopmental toxicity testing in vitro. Further assessment of DNT-specific biomarkers that represent these processes needs further studies.

Common network effect-patterns after monoamine reuptake inhibition in dissociated hippocampus cultures

The pharmacological treatment of major depressive disorder with currently available antidepressant drugs is still unsatisfying as response to medication is delayed and in some patients even non-existent. To understand complex psychiatric diseases such as major depressive disorder and their treatment, research focus is shifting from investigating single neurons towards a view of the entire functional and effective neuronal network, because alterations on single synapses through antidepressant drugs may translate to alterations in the entire network. Here, we examined the effects of monoamine reuptake inhibitors on in vitro hippocampal network dynamics using calcium fluorescence imaging and analyzing the data with means of graph theoretical parameters. Hypothesizing that monoamine reuptake inhibitors operate through changes of effective connectivity on micro-scale neuronal networks, we measured the effects of the selective monoamine reuptake inhibitors GBR-12783, Sertraline, Venlafaxine, and Amitriptyline on neuronal networks. We identified a common pattern of effects of the different tested monoamine reuptake inhibitors. After treatment with GBR-12783, Sertraline, and Venlafaxine, the connectivity degree, measuring the number of existing connections in the network, was significantly decreased. All tested substances led to networks with more submodules and a reduced global efficiency. No monoamine reuptake inhibitor did affect network-wide firing rate, the characteristic path length, or the network strength. In our study, we found that monoamine reuptake inhibition in neuronal networks in vitro results in a sharpening of the network structure. These alterations could be the basis for the reorganization of a large-scale miswired network in major depressive disorder.

Endoderm and mesoderm derivatives in embryonic stem cell differentiation and their use in developmental toxicity testing

Embryonic stem cell differentiation models have increasingly been applied in non-animal test systems for developmental toxicity. After the initial focus on cardiac differentiation, attention has also included an array of neuro-ectodermal differentiation routes. Alternative differentiation routes in the mesodermal and endodermal germ lines have received less attention. This review provides an inventory of achievements in the latter areas of embryonic stem cell differentiation, with a view to possibilities for their use in non-animal test systems in developmental toxicology. This includes murine and human stem cell differentiation models, and also gains information from the field of stem cell use in regenerative medicine. Endodermal stem cell derivatives produced in vitro include hepatocytes, pancreatic cells, lung epithelium, and intestinal epithelium, and mesodermal derivatives include cardiac muscle, osteogenic, vascular and hemopoietic cells. This inventory provides an overview of studies on the different cell types together with biomarkers and culture conditions that stimulate these differentiation routes from embryonic stem cells. These models may be used to expand the spectrum of embryonic stem cell based new approach methodologies in non-animal developmental toxicity testing.

Exploring the biological domain of the neural embryonic stem cell test (ESTn): Morphogenetic regulators, Hox genes and cell types, and their usefulness as biomarkers for embryotoxicity screening

Animal-free assessment of compound-induced developmental neurotoxicity will most likely be based on batteries of multiple in vitro tests. The optimal battery is built by combining tests with complementary biological domains that together ideally cover all relevant toxicity pathways. Thus, biological domain definition, i.e. which biological processes and cell types are represented, is an important assay characteristic for determining the place of assays in testing strategies. The murine neural embryonic stem cell test (ESTn) is employed to predict the developmental neurotoxicity of compounds. The aim of this study was to explore the biological domain of ESTn according to three groups of biomarker genes of early (neuro)development: morphogenetic regulators, Hox genes and cell type markers for the ectodermal and neural lineages. These biomarker groups were selected based on their crucial regulatory role in (neuro)development. Analysis of these genes in a series of previously generated whole transcriptome datasets of ESTn showed that at day 7 in culture cell differentiation resembled hindbrain/branchial/thoracic development between E6.5-E12.5 in vivo, with subsequent development into a mixed cell culture containing different neural subtypes, astrocytes and oligodendrocytes by day 13. In addition, the selected biomarkers showed common and distinct responses to compound exposure. Monitoring the biological domain of ESTn through gene expression patterns of morphogenetic regulators, Hox genes and cell type markers proved instrumental in providing mechanistic understanding of compound effects on neural differentiation in ESTn, and can aid in positioning of the test in a battery of complementary in vitro tests in integrated approaches to testing and assessment.

Fluoxetine Promotes Hippocampal Oligodendrocyte Maturation and Delays Learning and Memory Decline in APP/PS1 Mice

Oligodendrogenesis dysfunction impairs memory consolidation in adult mice, and an oligodendrocyte abnormality is an important change occurring in Alzheimer's disease (AD). While fluoxetine (FLX) is known to delay memory decline in AD models, its effects on hippocampal oligodendrogenesis are unclear. Here, we subjected 8-month-old male amyloid precursor protein (APP)/presenilin 1 (PS1) mice to the FLX intervention for 2 months. Their exploratory behaviors and general activities in a novel environment, spatial learning and memory and working and reference memory were assessed using the open-field test, Morris water maze, and Y maze. Furthermore, changes in hippocampal oligodendrogenesis were investigated using stereology, immunohistochemistry, immunofluorescence staining, and Western blotting techniques. FLX delayed declines in the spatial learning and memory, as well as the working and reference memory of APP/PS1 mice. In addition, APP/PS1 mice exhibited immature hippocampal oligodendrogenesis, and FLX increased the numbers of 2'3'cyclic nucleotide 3'-phosphodiesterase (CNPase)+ and newborn CNPase+ oligodendrocytes in the hippocampi of APP/PS1 mice. Moreover, FLX increased the density of SRY-related HMG-box 10 protein (SOX10)+ cells and reduced the percentage of oligodendrocyte lineage cells displaying the senescence phenotype (CDKN2A/p16INK4a) in the hippocampus of APP/PS1 mice. Moreover, FLX had no effect on the serotonin (5-HT) 1A receptor (5-HT1AR) content or number of 5-HT1AR+ oligodendrocytes, but it reduced the content and activity of glycogen synthase kinase 3β (GSK3β) in the hippocampus of APP/PS1 transgenic mice. Taken together, FLX delays the senescence of oligodendrocyte lineage cells and promotes oligodendrocyte maturation in the hippocampus of APP/PS1 mice. FLX may regulate GSK3β through a mechanism other than 5-HT1AR and then inhibit the negative effect of GSK3β on oligodendrocyte maturation in the hippocampus of an AD mouse model.

Culture Conditions Affect Chemical-Induced Developmental Toxicity In Vitro: The Case of Folic Acid, Methionine and Methotrexate in the Neural Embryonic Stem Cell Test

In vitro tests are increasingly applied in chemical hazard assessment. Basic culture conditions may affect the outcome of in vitro tests and should be optimised to reduce false predictions. The neural embryonic stem cell test (ESTn) can predict early neurodevelopmental effects of chemicals, as it mimics the differentiation of stem cells towards the neuroectodermal lineage. Normal early neural differentiation depends crucially on folic acid (FA) and methionine (MET), both elements of the one-carbon (1C) cycle. The aim of this study was to assess the concentration-dependent influence of FA and MET on neural differentiation in the ESTn, and its consequences for assay sensitivity to methotrexate (MTX), a compound that interferes with the 1C cycle. Neural differentiation was inhibited below 0.007 mM and above 0.22 mM FA, while both stem cell viability (< 0.097 mM, > 1.52 mM) and neural differentiation (< 0.181 mM, > 1.35 mM) were affected when changing MET concentrations. A 10-day exposure to 13 nM MTX inhibited neural differentiation, especially in FA- and MET-deficient conditions. However, a 24-hour exposure to 39 nM MTX decreased neural cell and neural crest cell differentiation markers only when the concentration of FA in the medium was three times the standard concentration, which was expected to have a protective effect against MTX. These results show the importance of nutrient concentrations, exposure scenarios and timing of read-outs for cell differentiation and compound sensitivity in the ESTn. Caution should be taken when interpreting results from a single in vitro test, especially when extrapolating to effects on complex morphogenetic processes, like neural tube development.