Evaluation of the rotenone-induced activation of the Nrf2 pathway in a neuronal model derived from human induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs): molecular mechanisms of induction and applications

The induced pluripotent stem cell (iPSC) technology has transformed in vitro research and holds great promise to advance regenerative medicine. iPSCs have the capacity for an almost unlimited expansion, are amenable to genetic engineering, and can be differentiated into most somatic cell types. iPSCs have been widely applied to model human development and diseases, perform drug screening, and develop cell therapies. In this review, we outline key developments in the iPSC field and highlight the immense versatility of the iPSC technology for in vitro modeling and therapeutic applications. We begin by discussing the pivotal discoveries that revealed the potential of a somatic cell nucleus for reprogramming and led to successful generation of iPSCs. We consider the molecular mechanisms and dynamics of somatic cell reprogramming as well as the numerous methods available to induce pluripotency. Subsequently, we discuss various iPSC-based cellular models, from mono-cultures of a single cell type to complex three-dimensional organoids, and how these models can be applied to elucidate the mechanisms of human development and diseases. We use examples of neurological disorders, coronavirus disease 2019 (COVID-19), and cancer to highlight the diversity of disease-specific phenotypes that can be modeled using iPSC-derived cells. We also consider how iPSC-derived cellular models can be used in high-throughput drug screening and drug toxicity studies. Finally, we discuss the process of developing autologous and allogeneic iPSC-based cell therapies and their potential to alleviate human diseases.

The identification of cianidanol as a selective estrogen receptor beta agonist and evaluation of its neuroprotective effects on Parkinson's disease models

AIM

The present study aims to identify selective estrogen receptor beta (ERβ) agonists and to evaluate the neuroprotective mechanism in Parkinson's disease (PD) models.

MAIN METHODS

In-silico studies were carried out using Maestro and GROMACS. Neuroprotective activity and apoptosis were evaluated using cytotoxicity assay and flow cytometry respectively. Gene expression studies were carried out by reverse transcription polymerase chain reaction. Motor and cognitive functions were assessed by actophotometer, rotarod, catalepsy, and elevated plus maze. The neuronal population in the substantia nigra and striatum of rats was assessed by hematoxylin and eosin staining.

KEY FINDINGS

Cianidanol was identified as a selective ERβ agonist through virtual screening. The cianidanol-ERβ complex is stable during the 200 ns simulation and was able to retain the interactions with key amino acid residues. Cianidanol (25 μM) prevents neuronal toxicity and apoptosis induced by rotenone in differentiated SH-SY5Y cells. Additionally, cianidanol (25 μM) increases the expression of ERβ, cathepsin D, and Nrf2 transcripts. The neuroprotective effects of cianidanol (25 μM) were reversed in the presence of a selective ERβ antagonist. In this study, we found that selective activation of ERβ could decrease the transcription of α-synuclein gene. Additionally, cianidanol (10, 20, 30 mg/kg, oral) improves the motor and cognitive deficit in rats induced by rotenone.

SIGNIFICANCE

Cianidanol shows neuroprotective action in PD models and has the potential to serve as a novel therapeutic agent for the treatment of PD.

The Mitochondrial-Derived Peptide (MOTS-c) Interacted with Nrf2 to Defend the Antioxidant System to Protect Dopaminergic Neurons Against Rotenone Exposure

MOTS-c is a 16-amino acid mitochondrial-derived peptide reported to be involved in regulating energy metabolism. However, few studies have reported the role of MOTS-c on neuron degeneration. In this study, it was aimed to explore the action of MOTS-c in rotenone-induced dopaminergic neurotoxicity. In an in vitro study, it was observed that rotenone could influence the expression and localization of MOTS-c significantly in PC12 cells, with more MOTS-c translocating into the nucleus from mitochondria. Further study showed that the translocation of MOTS-c from the mitochondria into the nucleus could directly interact with Nrf2 to regulate HO-1 and NQO1 expression in PC12 cells exposed to rotenone, which had been suggested to be involved in the antioxidant defense system. In vivo and in vitro experiments demonstrated that exogenous MOTS-c pretreatment could protect PC12 cells and rats from mitochondrial dysfunction and oxidative stress induced by rotenone. Moreover, MOTS-c pretreatment significantly decreased the loss of TH, PSD95, and SYP protein expression in the striatum of rats exposed to rotenone. In addition, MOTS-c pretreatment could clearly alleviate the downregulated expression of Nrf2, HO-1, and NQO1, as well as the upregulated Keap1 protein expression in the striatum of rotenone-treated rats. Taken together, these findings suggested that MOTS-c could directly interact with Nrf2 to activate the Nrf2/HO-1/NQO1 signal pathway to defend the antioxidant system to prevent dopaminergic neurons from rotenone-induced oxidative stress and neurotoxicity in vitro and in vivo.

Neuroprotective actions of a fatty acid nitroalkene in Parkinson's disease

To date there are no therapeutic strategies that limit the progression of Parkinson's disease (PD). The mechanisms underlying PD-related nigrostriatal neurodegeneration remain incompletely understood, with multiple factors modulating the course of PD pathogenesis. This includes Nrf2-dependent gene expression, oxidative stress, α-synuclein pathology, mitochondrial dysfunction, and neuroinflammation. In vitro and sub-acute in vivo rotenone rat models of PD were used to evaluate the neuroprotective potential of a clinically-safe, multi-target metabolic and inflammatory modulator, the electrophilic fatty acid nitroalkene 10-nitro-oleic acid (10-NO2-OA). In N27-A dopaminergic cells and in the substantia nigra pars compacta of rats, 10-NO2-OA activated Nrf2-regulated gene expression and inhibited NOX2 and LRRK2 hyperactivation, oxidative stress, microglial activation, α-synuclein modification, and downstream mitochondrial import impairment. These data reveal broad neuroprotective actions of 10-NO2-OA in a sub-acute model of PD and motivate more chronic studies in rodents and primates.

Effects of all-trans and 9-cis retinoic acid on differentiating human neural stem cells in vitro

Cyanobacterial blooms are known sources of environmentally-occurring retinoid compounds, including all-trans and 9-cis retinoic acids (RAs). The developmental hazard for aquatic organisms has been described, while the implications for human health hazard assessment are not yet sufficiently characterized. Here, we employ a human neural stem cell model that can differentiate in vitro into a mixed culture of neurons and glia. Cells were exposed to non-cytotoxic 8-1000 nM all-trans or 9-cis RA for 9-18 days (DIV13 and DIV22, respectively). Impact on biomarkers was analyzed on gene expression (RT-qPCR) and protein level (western blot and proteomics) at both time points; network patterning (immunofluorescence) on DIV22. RA exposure significantly concentration-dependently increased gene expression of retinoic acid receptors and the metabolizing enzyme CYP26A1, confirming the chemical-specific response of the model. Expression of thyroid hormone signaling-related genes remained mostly unchanged. Markers of neural progenitors/stem cells (PAX6, SOX1, SOX2, NESTIN) were decreased with increasing RA concentrations, though a basal population remained. Neural markers (DCX, TUJ1, MAP2, NeuN, SYP) remained unchanged or were decreased at high concentrations (200-1000 nM). Conversely, (astro-)glial marker S100β was increased concentration-dependently on DIV22. Together, the biomarker analysis indicates an RA-dependent promotion of glial cell fates over neural differentiation, despite the increased abundance of neural protein biomarkers during differentiation. Interestingly, RA exposure induced substantial changes to the cell culture morphology: while low concentrations resulted in a network-like differentiation pattern, high concentrations (200-1000 nM RA) almost completely prevented such network patterning. After functional confirmation for implications in network function, such morphological features could present a proxy for network formation assessment, an apical key event in (neuro-)developmental Adverse Outcome Pathways. The described application of a human in vitro model for (developmental) neurotoxicity to emerging environmentally-relevant retinoids contributes to the evidence-base for the use of differentiating human in vitro models for human health hazard and risk assessment.

Assessment of neurotransmitter release in human iPSC-derived neuronal/glial cells: a missing in vitro assay for regulatory developmental neurotoxicity testing

Human induced pluripotent stem cell (hiPSC)-derived neural stem cells (NSCs) and their differentiated neuronal/glial derivatives have been recently considered suitable to assess in vitro developmental neurotoxicity (DNT) triggered by exposure to environmental chemicals. The use of human-relevant test systems combined with in vitro assays specific for different neurodevelopmental events, enables a mechanistic understanding of the possible impact of environmental chemicals on the developing brain, avoiding extrapolation uncertainties associated with in vivo studies. Currently proposed in vitro battery for regulatory DNT testing accounts for several assays suitable to study key neurodevelopmental processes, including NSC proliferation and apoptosis, differentiation into neurons and glia, neuronal migration, synaptogenesis, and neuronal network formation. However, assays suitable to measure interference of compounds with neurotransmitter release or clearance are at present not included, which represents a clear gap of the biological applicability domain of such a testing battery. Here we applied a HPLC-based methodology to measure the release of neurotransmitters in a previously characterized hiPSC-derived NSC model undergoing differentiation towards neurons and glia. Glutamate release was assessed in control cultures and upon depolarization, as well as in cultures repeatedly exposed to some known neurotoxicants (BDE47 and lead) and chemical mixtures. Obtained data indicate that these cells have the ability to release glutamate in a vesicular manner, and that both glutamate clearance and vesicular release concur in the maintenance of extracellular glutamate levels. In conclusion, analysis of neurotransmitter release is a sensitive readout that should be included in the envisioned battery of in vitro assays for DNT testing.

Prolonged Differentiation of Neuron-Astrocyte Co-Cultures Results in Emergence of Dopaminergic Neurons

Dopamine is present in a subgroup of neurons that are vital for normal brain functioning. Disruption of the dopaminergic system, e.g., by chemical compounds, contributes to the development of Parkinson's disease and potentially some neurodevelopmental disorders. Current test guidelines for chemical safety assessment do not include specific endpoints for dopamine disruption. Therefore, there is a need for the human-relevant assessment of (developmental) neurotoxicity related to dopamine disruption. The aim of this study was to determine the biological domain related to dopaminergic neurons of a human stem cell-based in vitro test, the human neural progenitor test (hNPT). Neural progenitor cells were differentiated in a neuron-astrocyte co-culture for 70 days, and dopamine-related gene and protein expression was investigated. Expression of genes specific for dopaminergic differentiation and functioning, such as LMX1B, NURR1, TH, SLC6A3, and KCNJ6, were increasing by day 14. From day 42, a network of neurons expressing the catecholamine marker TH and the dopaminergic markers VMAT2 and DAT was present. These results confirm stable gene and protein expression of dopaminergic markers in hNPT. Further characterization and chemical testing are needed to investigate if the model might be relevant in a testing strategy to test the neurotoxicity of the dopaminergic system.

Involvement of Nrf2 in the immune regulation of Litopenaeus vannamei against Vibrio harveyi infection

NF-E2-related factor-like-2 (Nrf2) is a transcription factor that belongs to the Cap'n'Collar transcription factor family and plays a role in regulating inflammation, autophagy, metabolism, proteostasis, and cancer prevention. However, its influence on Vibrio spp infection in L. vannamei remains uncertain. In this study, the effects of Nrf2 on the immune response in Vibrio spp infection was determined by RT-PCR and histopathological analysis. The results showed that RNAi of Nrf2 significantly decreased the expression of antioxidant-related genes (CAT, SOD and GST; p < 0.05), and significantly up-regulated inflammation-related genes (IMD, pro-PO, P38, Toll, Hsp70, NFκB and RAB6A; p < 0.05) and the apoptosis gene (caspase3). Under the infection of V. harveyi, histopathological analysis showed that after RNAi of Nrf2, the hepatopancreas of shrimp has an abnormal arrangement of hepatic tubules and vacuolization of hepatocyte; The basement membrane is peeled off and the epithelial cells are massively necrotic. Compared with the RNAi of Nrf2 group, the tissue damage in the SFN group was much lessened, and there were fewer apoptosis signals in the TUNEL assay. In conclusion, this experiment indicated that Nrf2 is involved in the regulation of inflammatory response, oxidative stress,and apoptosis induced by V. harveyi in L. vannamei.

Vitamin D3 actions on astrocyte cells: A target for therapeutic strategy in Parkinson's disease?

Parkinson's disease (PD) is a neurodegenerative disease characterized by the loss of dopaminergic cells in the substantia nigra pars compacta. PD patients' brains show neuroinflammation, oxidative stress, and mitochondrial dysfunction. The present study aims to evaluate the neuroprotective activity of VD3 on astrocytes after their exposure to rotenone (ROT) a natural pesticide known to exhibit neurotoxic potential via the inhibition of mitochondrial complex I. Cell viability parameters were evaluated by the MTT test and staining with 7-AAD in cultures of astrocytes treated and untreated with VD3 (0.1, 0.5, and 1.0 ng/mL) and/or ROT (10 µg/mL or 5 µg/mL), and the cytoplasmic production of ROS and the cell death profile were measured by flow cytometry. Glutathione accumulation and ultrastructural changes were evaluated and immunocytochemistry assays for NF-kB and Nrf2 were also carried out. The results showed that VD3 improved the viability of cells previously treated with VD3 and then exposed to ROT, reducing the occurrence of necrotic and apoptotic events. Furthermore, cells exposed to ROT showed increased production of ROS, which decreased significantly with previous treatment with VD3. Importantly, the decrease by ROT in the mitochondrial transmembrane potential was significantly prevented after treating cells with VD3, especially at a concentration of 1 ng/mL. Therefore, treatment with VD3 protected astrocytes from damage caused by ROT, decreasing oxidative stress, decreasing NF-kB and Nrf2 expressions, and improving mitochondrial function. However, further investigation is needed regarding the participation and mechanism of action of VD3 in this cellular model of PD focusing on the crosstalk between Nrf2 and NF-kB.

Bilirubin Prevents the TH+ Dopaminergic Neuron Loss in a Parkinson's Disease Model by Acting on TNF-α

Parkinson's disease (PD), the fastest-growing movement disorder, is still challenged by the unavailability of disease-modifying therapy. Mildly elevated levels of unconjugated bilirubin (UCB, PubChem CID 5280352) have been shown to be protective against several extra-CNS diseases, and the effect is attributed to its well-known anti-oxidant and anti-inflammatory capability. We explored the neuroprotective effect of low concentrations of UCB (from 0.5 to 4 µM) in our PD model based on organotypic brain cultures of substantia nigra (OBCs-SN) challenged with a low dose of rotenone (Rot). UCB at 0.5 and 1 µM fully protects against the loss of TH⁺ (dopaminergic) neurons (DOPAn). The alteration in oxidative stress is involved in TH⁺ positive neuron demise induced by Rot, but is not the key player in UCB-conferred protection. On the contrary, inflammation, specifically tumor necrosis factor alpha (TNF-α), was found to be the key to UCB protection against DOPAn sufferance. Further work will be needed to introduce the use of UCB into clinical settings, but determining that TNF-α plays a key role in PD may be crucial in designing therapeutic options.

Natural Compounds Such as Hericium erinaceus and Coriolus versicolor Modulate Neuroinflammation, Oxidative Stress and Lipoxin A4 Expression in Rotenone-Induced Parkinson's Disease in Mice

BACKGROUND

A growing body of research suggests that oxidative stress and neuroinflammation are early pathogenic features of neurodegenerative disorders. In recent years, the vitagene system has emerged as a potential target, as it has been shown to have a high neuroprotective power. Therefore, the discovery of molecules capable of activating this system may represent a new therapeutic target to limit the deleterious consequences induced by oxidative stress and neuroinflammation, such as neurodegeneration. Lipoxins are derived from arachidonic acid, and their role in the resolution of systemic inflammation is well established; however, they have become increasingly involved in the regulation of neuroinflammatory and neurodegenerative processes. Our study aimed at activating the NF-E2-related factor 2 (Nrf2)/heme oxygenase 1 (HO-1) redox system and increasing lipoxin A4 for the modulation of antioxidant stress and neuroinflammation through the action of two fungi in a rotenone-induced Parkinson's model.

METHODS

During the experiment, mice received Hericium erinaceus, Coriolus versicolor or a combination of the two (200 mg/kg, orally) concomitantly with rotenone (5 mg/kg, orally) for 28 days.

RESULTS

The results obtained highlighted the ability of these two fungi and, in particular, their ability through their association to act on neuroinflammation through the nuclear factor-kB pathway and on oxidative stress through the Nrf2 pathway. This prevented dopaminergic neurons from undergoing apoptosis and prevented the alteration of typical Parkinson's disease (PD) markers and α-synuclein accumulation. The action of Hericium erinaceus and Coriolus versicolor was also able to limit the motor and non-motor alterations characteristic of PD.

CONCLUSIONS

Since these two mushrooms are subject to fewer regulations than traditional drugs, they could represent a promising nutraceutical choice for preventing PD.

Neuroprotective and therapeutic effects of calcitriol in rotenone-induced Parkinson’s disease rat model

Parkinson’s disease (PD) is the second most common neurodegenerative disease. Treatment of PD is challenging, as current treatment strategies are only symptomatic and do not stop disease development. Recent studies reported neuroprotective effects of calcitriol in PD through its antioxidant and anti-inflammatory properties. The exact pathomechanisms of PD are not yet fully understood. So, investigation of different molecular pathways is challenging. Sirtuin-1 (Sirt1) modulates multiple physiological processes, including programmed cell death, DNA repair, and inflammation. Furthermore, defective autophagy is considered a key pathomechanism in PD as it eliminates protein aggregation and dysfunctional cell organelles. The present study investigated the involvement of autophagy and Sirt1/NF-κB molecular pathway in rotenone-induced PD and explored the protective and restorative effects of calcitriol through these mechanisms. Therefore, behavioral tests were used to test the effect of calcitriol on motor disability and equilibrium. Furthermore, the histological and neuronal architecture was assessed. The expression of genes encoding neuroinflammation and autophagy markers was determined by qPCR while their protein levels were determined by Western blot analysis and immune-histochemical staining. Our results indicate that behavioral impairments and dopaminergic neuron depletion in the rotenone-induced PD model were improved by calcitriol administration. Furthermore, calcitriol attenuated rotenone-induced neuroinflammation and autophagy dysfunction in PD rats through up-regulation of Sirt1 and LC3 and down-regulation of P62 and NF-κB expression levels. Thus, calcitriol could induce a neuro-protective and restorative effect in the rotenone-induced PD model by modulating autophagy and Sirt1/NF-κB pathway.

β-Lapachone, an NQO1 activator, alleviates diabetic cardiomyopathy by regulating antioxidant ability and mitochondrial function

BACKGROUND

Diabetic cardiomyopathy (DC) is one of the major lethal complications in patients with diabetes mellitus (DM); however, no specific strategy for preventing or treating DC has been identified.

PURPOSE

This study aimed to investigate the effects of β-lapachone (Lap), a natural compound that increases antioxidant activity in various tissues, on DC and explore the underlying mechanisms.

STUDY DESIGN AND METHODS

As an in vivo model, C57BL/6 mice were fed with the high-fat diet (HF) for 10 weeks to induce type 2 DM. Mice were fed Lap with the HF or after 5 weeks of HF treatment to investigate the protective effects of Lap against DC.

RESULTS

In the two in vivo models, Lap decreased heart weight, increased heart function, reduced oxidative stress, and elevated mitochondrial content under the HF. In the in vitro model, palmitic acid (PA) was used to mimic the effects of an HF on the differentiated-cardiomyoblast cell line H9c2. The results demonstrated that Lap reduced PA-induced ROS production by increasing the expression of antioxidant regulators and enzymes, inhibiting inflammation, increasing mitochondrial activity, and thus reducing cell damage. Via the use of specific inhibitors and siRNA, the protective effects of Lap were determined to be mediated mainly by NQO1, Sirt1 and mitochondrial activity.

CONCLUSION

Heart damage in DM is usually caused by excessive oxidative stress. This study showed that Lap can protect the heart from DC by upregulating antioxidant ability and mitochondrial activity in cardiomyocytes. Lap has the potential to serve as a novel therapeutic agent for both the prevention and treatment of DC.

Brain Pericytes Acquire Stemness via the Nrf2-Dependent Antioxidant System

Pericytes (PCs) are a mural support cell population elongated at intervals along the walls of capillaries. Recent studies reported that PCs are multipotent cells that are activated in response to tissue injury and contribute to the regenerative process. Using a C.B-17 mouse model of ischemic stroke, it has been proposed that normal brain pericytes (nPCs) are converted to ischemic pericytes (iPCs), some of which function as multipotent stem cells. Furthermore, oxygen-glucose deprivation (OGD) promoted mesenchymal-epithelial transition in nPCs; however, nestin was not induced under OGD conditions. Therefore, further studies are needed to elucidate the PC reprogramming phenomenon. We herein isolated nPCs from the cortex of C.B-17 mice, and compared the traits of iPCs and nPCs. The results obtained showed that nPCs and iPCs shared common pericytic markers. Furthermore, intercellular levels of reactive oxygen species and the nuclear accumulation of nuclear factor erythroid-2-related factor 2 (Nrf2), a key player in antioxidant defenses, were higher in iPCs than in nPCs. OGD/reoxygenation and a treatment with tBHQ, an Nrf2 inducer, increased nestin levels in nPCs. Moreover, epithelial marker levels, including nestin, Sox2, and CDH1 (E-cadherin) mRNAs, were elevated in Nrf2-overexpressing PCs, which formed neurosphere-like cell clusters that differentiated into Tuj1-positive neurons. The present results demonstrate that oxidative stress and Nrf2 are required for the generation of stem cells after stroke and will contribute to the development of novel therapeutic strategies for ischemic stroke.

Developmental neurotoxicity of acrylamide and its metabolite glycidamide in a human mixed culture of neurons and astrocytes undergoing differentiation in concentrations relevant for human exposure

Neural stem cells (NSCs) derived from human induced pluripotent stem cells were used to investigate effects of exposure to the food contaminant acrylamide (AA) and its main metabolite glycidamide (GA) on key neurodevelopmental processes. Diet is an important source of human AA exposure for pregnant women, and AA is known to pass the placenta and the newborn may also be exposed through breast feeding after birth. The NSCs were exposed to AA and GA (1 ×10^-8 - 3 ×10^-3 M) under 7 days of proliferation and up to 28 days of differentiation towards a mixed culture of neurons and astrocytes. Effects on cell viability was measured using Alamar Blue™ cell viability assay, alterations in gene expression were assessed using real time PCR and RNA sequencing, and protein levels were quantified using immunocytochemistry and high content imaging. Effects of AA and GA on neurodevelopmental processes were evaluated using endpoints linked to common key events identified in the existing developmental neurotoxicity adverse outcome pathways (AOPs). Our results suggest that AA and GA at low concentrations (1 ×10^-7 - 1 ×10^-8 M) increased cell viability and markers of proliferation both in proliferating NSCs (7 days) and in maturing neurons after 14-28 days of differentiation. IC₅₀ for cell death of AA and GA was 5.2 × 10^-3 M and 5.8 × 10^-4 M, respectively, showing about ten times higher potency for GA. Increased expression of brain derived neurotrophic factor (BDNF) concomitant with decreased synaptogenesis were observed for GA exposure (10^-7 M) only at later differentiation stages, and an increased number of astrocytes (up to 3-fold) at 14 and 21 days of differentiation. Also, AA exposure gave tendency towards decreased differentiation (increased percent Nestin positive cells). After 28 days, neurite branch points and number of neurites per neuron measured by microtubule-associated protein 2 (Map2) staining decreased, while the same neurite features measured by βIII-Tubulin increased, indicating perturbation of neuronal differentiation and maturation.

Upscaling biological complexity to boost neuronal and oligodendroglia maturation and improve in vitro developmental neurotoxicity (DNT) evaluation

Human induced pluripotent stem cell (iPSC)-derived neuronal and glial cell models are suitable to assess the effects of environmental chemicals on the developing brain. Such test systems can recapitulate several key neurodevelopmental features, such as neural stem cell formation and differentiation towards different neuronal subtypes and astrocytes, neurite outgrowth, synapse formation and neuronal network formation and function, which are crucial for brain development. While monolayer, two-dimensional (2D) cultures of human iPSC-neuronal or glial derivatives are generally suited for high-throughput testing, they also show some limitations. In particular, differentiation towards myelinating oligodendrocytes can only be achieved after extended periods in differentiation. In recent years, the implementation of three-dimensional (3D) neuronal and glial models obtained from human iPSCs has been shown to compensate for such limitations, enabling robust differentiation towards both neuronal and glial cell populations, myelination and formation of more mature neuronal network activity. Here we compared the differentiation capacity of human iPSC-derived neural stem cells cultured either as 2D monolayer or as 3D neurospheres, and assessed chlorpyrifos (CPF) effects. Data indicate that 3D neurospheres differentiate towards neurons and oligodendroglia more rapidly than 2D cultures; however, the 2D model is more suitable to assess neuronal functionality by analysis of spontaneous electrical activity using multielectrode array. Moreover, 2D and 3D test systems are diversely susceptible to CPF treatment. In conclusion, the selection of the most suitable in vitro test system (either 2D or 3D) should take into account the context of use and intended research goals ('fit for purpose' principle).

The principal molecular mechanisms behind the activation of Keap1/Nrf2/ARE pathway leading to neuroprotective action in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder. PD is associated with the loss of dopaminergic neurons in the substantia nigra pars compacta region of the midbrain. Present therapies for PD provide only symptomatic relief by restoring the dopamine (DA) level. However, they are not disease modifying agents and so they do not delay the disease progression. Alpha-synuclein aggregation, oxidative stress, mitochondrial dysfunction and chronic inflammation are considered to be the major pathological mechanisms mediating neurodegeneration in PD. To resist oxidative stress, the human body has an antioxidant defence mechanism consisting of many antioxidants and cytoprotective genes. The expression of those genes are largely controlled by the Kelch-like ECH-associated protein 1/Nuclear factor - erythroid - 2 - related factor 2/Antioxidant response element (Keap1/Nrf2/ARE) signalling pathway. The transcription factor Nrf2 is activated in response to oxidative or electrophilic stress and protects the cells from oxidative stress and inflammation. Nrf2 has been widely considered as a therapeutic target for neurodegeneration and several drugs are now being tested in clinical trials. Regulation of the Keap1/Nrf2/ARE pathway by small molecules which can act as Nrf2 activators could be effective for treating oxidative stress and neuroinflammation in PD. In this review, we had discussed the principal molecular mechanisms behind the neuroprotective effects of Keap1/Nrf2/ARE pathway in PD. Additionally, we also discussed the small molecules and phytochemicals that could activate the Nrf2 mediated anti-oxidant pathway for neuroprotection in PD.

Induced Pluripotent Stem Cells and Hormesis

This paper represents the first assessment of agent-induced hormetic dose responses in induced pluripotent stem cells and their derived cells. The hormetic dose responses were induced by a broad range of chemicals, including pharmaceuticals (eg, metformin), dietary supplements/extracts from medicinal plants (eg, curcumin), and endogenous agents (eg, melatonin). The paper assesses the mechanistic foundations of these induced hormetic dose responses, their therapeutic implications and comparison with hormetic responses in multiple adult and embryonic stem cells.

Combining in vitro assays and mathematical modelling to study developmental neurotoxicity induced by chemical mixtures

Prenatal and postnatal co-exposure to multiple chemicals at the same time may have deleterious effects on the developing nervous system. We previously showed that chemicals acting through similar mode of action (MoA) and grouped based on perturbation of brain derived neurotrophic factor (BDNF), induced greater neurotoxic effects on human induced pluripotent stem cell (hiPSC)-derived neurons and astrocytes compared to chemicals with dissimilar MoA. Here we assessed the effects of repeated dose (14 days) treatments with mixtures containing the six chemicals tested in our previous study (Bisphenol A, Chlorpyrifos, Lead(II) chloride, Methylmercury chloride, PCB138 and Valproic acid) along with 2,2'4,4'-tetrabromodiphenyl ether (BDE47), Ethanol, Vinclozolin and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)), on hiPSC-derived neural stem cells undergoing differentiation toward mixed neurons/astrocytes up to 21 days. Similar MoA chemicals in mixtures caused an increase of BDNF levels and neurite outgrowth, and a decrease of synapse formation, which led to inhibition of electrical activity. Perturbations of these endpoints are described as common key events in adverse outcome pathways (AOPs) specific for DNT. When compared with mixtures tested in our previous study, adding similarly acting chemicals (BDE47 and EtOH) to the mixture resulted in a stronger downregulation of synapses. A synergistic effect on some synaptogenesis-related features (PSD95 in particular) was hypothesized upon treatment with tested mixtures, as indicated by mathematical modelling. Our findings confirm that the use of human iPSC-derived mixed neuronal/glial models applied to a battery of in vitro assays anchored to key events in DNT AOP networks, combined with mathematical modelling, is a suitable testing strategy to assess in vitro DNT induced by chemical mixtures.

Nanoemulsion Improves the Neuroprotective Effects of Curcumin in an Experimental Model of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor dysfunction. Recent studies have shown that curcumin (CUR) has neuroprotective effects in PD experimental models. However, its efficacy is limited due to low water solubility, bioavailability, and access to the central nervous system. In this study, we compared the effects of new curcumin-loaded nanoemulsions (NC) and free CUR in an experimental model of PD. Adult Swiss mice received NC or CUR (25 and 50 mg/kg) or vehicle orally for 30 days. Starting on the eighth day, they were administered rotenone (1 mg/kg) intraperitoneally until the 30th day. At the end of the treatment, motor assessment was evaluated by open field, pole test, and beam walking tests. Oxidative stress markers and mitochondrial complex I activity were measured in the brain tissue. Both NC and CUR treatment significantly improved motor impairment, reduced lipoperoxidation, modified antioxidant defenses, and prevented inhibition of complex I. However, NC was more effective in preventing motor impairment and inhibition of complex I when compared to CUR in the free form. In conclusion, our results suggest that NC effectively enhances the neuroprotective potential of CUR and is a promising nanomedical application for PD.

Can Cranberry Juice Protect against Rotenone-Induced Toxicity in Rats?

The high polyphenols content of cranberry accounts for its strong antioxidant activity underlying the beneficial health effects of this fruit. Rotenone (ROT) is a specific inhibitor of mitochondrial complex I in the brain which leads to the generation of oxidative stress. To date, there are few data indicating that toxicity of ROT is not limited to the brain but can also affect other tissues. We aimed to examine whether ROT-induced oxidative stress could be counteracted by cranberry juice not only in the brain but also in the liver and kidney. Wistar rats were given the combined treatment with ROT and cranberry juice (CJ) for 35 days. Parameters of antioxidant status were determined in the organs. ROT enhanced lipid peroxidation solely in the brain. The increase in the DNA damage was noticed in all organs examined and in leukocytes. The beneficial effect of CJ on these parameters appeared only in the brain. Additionally, CJ decreased the activity of serum hepatic enzymes. The effect of CJ on antioxidant enzymes was not consistent, however, in some organs, CJ reversed changes evoked by ROT. Summing up, ROT can cause oxidative damage not only in the brain but also in other organs. CJ demonstrated a protective effect against ROT-induced toxicity.

Exposure to human relevant mixtures of halogenated persistent organic pollutants (POPs) alters neurodevelopmental processes in human neural stem cells undergoing differentiation

Halogenated persistent organic pollutants (POPs) like perfluorinated alkylated substances (PFASs), brominated flame retardants (BFRs), organochlorine pesticides and polychlorinated biphenyls (PCBs) are known to cause cancer, immunotoxicity, neurotoxicity and interfere with reproduction and development. Concerns have been raised about the impact of POPs upon brain development and possibly neurodevelopmental disorders. The developing brain is a particularly vulnerable organ due to dynamic and complex neurodevelopmental processes occurring early in life. However, very few studies have reported on the effects of POP mixtures at human relevant exposures, and their impact on key neurodevelopmental processes using human in vitro test systems. Aiming to reduce this knowledge gap, we exposed mixed neuronal/glial cultures differentiated from neural stem cells (NSCs) derived from human induced pluripotent stem cells (hiPSCs) to reconstructed mixtures of 29 different POPs using concentrations comparable to Scandinavian human blood levels. Effects of the POP mixtures on neuronal proliferation, differentiation and synaptogenesis were evaluated using in vitro assays anchored to common key events identified in the existing developmental neurotoxicity (DNT) adverse outcome pathways (AOPs). The present study showed that mixtures of POPs (in particular brominated and chlorinated compounds) at human relevant concentrations increased proliferation of NSCs and decreased synapse number. Based on a mathematical modelling, synaptogenesis and neurite outgrowth seem to be the most sensitive DNT in vitro endpoints. Our results indicate that prenatal exposure to POPs may affect human brain development, potentially contributing to recently observed learning and memory deficits in children.

Neonatal Rotenone Administration Induces Psychiatric Disorder-Like Behavior and Changes in Mitochondrial Biogenesis and Synaptic Proteins in Adulthood

Since psychiatric disorders are associated with changes in the development of the nervous system, an energy-dependent mechanism, we investigated whether mitochondrial inhibition during the critical neurodevelopment window in rodents would be able to induce metabolic alterations culminating in psychiatric-like behavior. We treated male Wistar rat puppies (P) with rotenone (Rot), an inhibitor of mitochondrial complex I, from postnatal days 5 to 11 (P5-P11). We demonstrated that at P60 and P120, Rot-treated animals showed hyperlocomotion and deficits in social interaction and aversive contextual memory, features observed in animal models of schizophrenia, autism spectrum disorder, and attention deficit hyperactivity disorder. During adulthood, Rot-treated rodents also presented modifications in CBP and CREB levels in addition to a decrease in mitochondrial biogenesis and Nrf1 expression. Additionally, NFE2L2-activation was not altered in Rot-treated P60 and P120 animals; an upregulation of pNFE2L2/ NFE2L2 was only observed in P12 cortices. Curiously, ATP/ADP levels did not change in all ages evaluated. Rot administration in newborn rodents also promoted modification in Rest and Mecp2 expression, and in synaptic protein levels, named PSD-95, Synaptotagmin-1, and Synaptophysin in the adult rats. Altogether, our data indicate that behavioral abnormalities and changes in synaptic proteins in adulthood induced by neonatal Rot administration might be a result of adjustments in CREB pathways and alterations in mitochondrial biogenesis and Nrf1 expression, rather than a direct deficiency of energy supply, as previously speculated. Consequently, Rot-induced psychiatric-like behavior would be an outcome of alterations in neuronal paths due to mitochondrial deregulation.

Intranasal Administration of Rotenone Reduces GABAergic Inhibition in the Mouse Insular Cortex Leading to Impairment of LTD and Conditioned Taste Aversion Memory

The pesticide rotenone inhibits mitochondrial complex I and is thought to cause neurological disorders such as Parkinson’s disease and cognitive disorders. However, little is known about the effects of rotenone on conditioned taste aversion memory. In the present study, we investigated whether intranasal administration of rotenone affects conditioned taste aversion memory in mice. We also examined how the intranasal administration of rotenone modulates synaptic transmission and plasticity in layer V pyramidal neurons of the mouse insular cortex that is critical for conditioned taste aversion memory. We found that the intranasal administration of rotenone impaired conditioned taste aversion memory to bitter taste. Regarding its cellular mechanisms, long-term depression (LTD) but not long-term potentiation (LTP) was impaired in rotenone-treated mice. Furthermore, spontaneous inhibitory synaptic currents and tonic GABA currents were decreased in layer V pyramidal neurons of rotenone-treated mice compared to the control mice. The impaired LTD observed in pyramidal neurons of rotenone-treated mice was restored by a GABA_A receptor agonist muscimol. These results suggest that intranasal administration of rotenone decreases GABAergic synaptic transmission in layer V pyramidal neurons of the mouse insular cortex, the result of which leads to impairment of LTD and conditioned taste aversion memory.

Integrating biokinetics and in vitro studies to evaluate developmental neurotoxicity induced by chlorpyrifos in human iPSC-derived neural stem cells undergoing differentiation towards neuronal and glial cells

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Human iPSC-derived NSCs undergoing differentiation possess some metabolic competence.

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CPF entered the cells and was biotrasformed into its two main metabolites (CPFO and TCP).

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After repeated exposure, very limited bioaccumulation of CPF was observed.

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Treatment with CPF decreased neurite outgrowth, synapse number and electrical activity.

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Treatment with CPF increased BDNF levels and the percentage of astrocytes.

For some complex toxicological endpoints, chemical safety assessment has conventionally relied on animal testing. Apart from the ethical issues, also scientific considerations have been raised concerning the traditional approach, highlighting the importance for considering real life exposure scenario. Implementation of flexible testing strategies, integrating multiple sources of information, including in vitro reliable test methods and in vitro biokinetics, would enhance the relevance of the obtained results. Such an approach could be pivotal in the evaluation of developmental neurotoxicity (DNT), especially when applied to human cell-based models, mimicking key neurodevelopmental processes, relevant to human brain development.

Here, we integrated the kinetic behaviour with the toxicodynamic alterations of chlorpyrifos (CPF), such as in vitro endpoints specific for DNT evaluation, after repeated exposure during differentiation of human neural stem cells into a mixed culture of neurons and astrocytes. The upregulation of some cytochrome P450 and glutathione S-transferase genes during neuronal differentiation and the formation of the two major CPF metabolites (due to bioactivation and detoxification) supported the metabolic competence of the used in vitro model. The alterations in the number of synapses, neurite outgrowth, brain derived neurotrophic factor, the proportion of neurons and astrocytes, as well as spontaneous electrical activity correlated well with the CPF ability to enter the cells and be bioactivated to CPF-oxon. Overall, our results confirm that combining in vitro biokinetics and assays to evaluate effects on neurodevelopmental endpoints in human cells should be regarded as a key strategy for a quantitative characterization of DNT effects.

Anti-inflammatory and Anti-oxidant Activity of Hidrox® in Rotenone-Induced Parkinson's Disease in Mice

BACKGROUND

In developed countries, the extension of human life is increasingly accompanied by a progressive increase in neurodegenerative diseases, most of which do not yet have effective therapy but only symptomatic treatments. In recent years, plant polyphenols have aroused considerable interest in the scientific community. The mechanisms currently hypothesized for the pathogenesis of Parkinson's disease (PD) are neuroinflammation, oxidative stress and apoptosis. Hydroxytyrosol (HT), the main component of Hidrox^® (HD), has been shown to have some of the highest free radical evacuation and anti-inflammatory activities. Here we wanted to study the role of HD on the neurobiological and behavioral alterations induced by rotenone.

METHODS

A study was conducted in which mice received HD (10 mg/kg, i.p.) concomitantly with rotenone (5 mg/kg, o.s.) for 28 days.

RESULTS

Locomotor activity, catalepsy, histological damage and several characteristic markers of the PD, such as the dopamine transporter (DAT) content, tyrosine hydroxylase (TH) and accumulation of α-synuclein, have been evaluated. Moreover, we observed the effects of HD on oxidative stress, neuroinflammation, apoptosis and inflammasomes. Taken together, the results obtained highlight HD's ability to reduce the loss of dopaminergic neurons and the damage associated with it by counteracting the three main mechanisms of PD pathogenesis.

CONCLUSION

HD is subject to fewer regulations than traditional drugs to improve patients' brain health and could represent a promising nutraceutical choice to prevent PD.

Biochemical Evaluation of the Antioxidant Effects of Hydroxytyrosol on Pancreatitis-Associated Gut Injury

Acute pancreatitis is a severe abdominal pathology often associated with several complications including gut dysfunction. Oxidative stress is one of the most important pathways involved in this pathology. Hydroxytyrosol (HT), a phenolic compound obtained from olive oil, has shown anti-inflammatory and antioxidant properties. We evaluated the effects of HT administration on pancreatic and intestinal injury induced by caerulein administration. CD1 female mice were administered caerulein (50 μg/kg) for 10 h. HT treatment (5 mg/kg) was performed 30 min after the first caerulein injection and for two consecutive hours afterwards. One hour after the last caerulein injection, mice were sacrificed and serum, colon and pancreatic tissue samples were collected. HT was able to reduce the serum hallmarks of pancreatitis (amylase and lipase), histological damage score in both pancreas and colon tissue, inflammatory cells recruitment (mast cells) in both injured tissues, intrapancreatic trypsin activity and overexpression of the adhesion molecules (Intercellular Adhesion Molecule-1 (ICAM-1) and P-selectin) in colon. Additionally, HT reduced cytokine (interleukin 1 beta (IL- 1β), interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α)) levels in serum, pancreas and colon tissue and chemokine release (monocyte chemotactic protein-1 (MCP1/CCL2)) in pancreas and colon tissue. HT decreased lipid peroxidation and oxidative stress (superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione S-transferase (GST) activity) by enhancing the nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) in both injured tissues. Moreover, HT preserved intestinal barrier integrity, as shown by the diamine oxidase (DAO) serum levels and tight junction (zonula occludens (ZO) and occludin) expression in pancreas and colon. Our findings demonstrated that HT would be an important therapeutic tool against pancreatitis-induced injuries in the pancreas and gut.

Redox toxicology of environmental chemicals causing oxidative stress

Living organisms are surrounded with heavy metals such as methylmercury, manganese, cobalt, cadmium, arsenic, as well as pesticides such as deltamethrin and paraquat, or atmospheric pollutants such as quinone. Extensive studies have demonstrated a strong link between environmental pollutants and human health. Redox toxicity is proposed as one of the main mechanisms of chemical-induced pathology in humans. Acting as both a sensor of oxidative stress and a positive regulator of antioxidants, the nuclear factor erythroid 2-related factor 2 (NRF2) has attracted recent attention. However, the role NRF2 plays in environmental pollutant-induced toxicity has not been systematically addressed. Here, we characterize NRF2 function in response to various pollutants, such as metals, pesticides and atmospheric quinones. NRF2 related signaling pathways and epigenetic regulations are also reviewed.

Human Induced Pluripotent Stem Cell-Derived 3D-Neurospheres are Suitable for Neurotoxicity Screening

We present a hiPSC-based 3D in vitro system suitable to test neurotoxicity (NT). Human iPSCs-derived 3D neurospheres grown in 96-well plate format were characterized timewise for 6-weeks. Changes in complexity and homogeneity were followed by immunocytochemistry and transmission electron microscopy. Transcriptional activity of major developmental, structural, and cell-type-specific markers was investigated at weekly intervals to present the differentiation of neurons, astrocytes, and oligodendrocytes. Neurospheres were exposed to different well-known toxicants with or without neurotoxic effect (e.g., paraquat, acrylamide, or ibuprofen) and examined at various stages of the differentiation with an ATP-based cell viability assay optimized for 3D-tissues. Concentration responses were investigated after acute (72 h) exposure. Moreover, the compound-specific effect of rotenone was investigated by a panel of ER-stress assay, TUNEL assay, immunocytochemistry, electron microscopy, and in 3D-spheroid based neurite outgrowth assay. The acute exposure to different classes of toxicants revealed distinct susceptibility profiles in a differentiation stage-dependent manner, indicating that hiPSC-based 3D in vitro neurosphere models could be used effectively to evaluate NT, and can be developed further to detect developmental neurotoxicity (DNT) and thus replace or complement the use of animal models in various basic research and pharmaceutical applications.

Characterization and application of electrically active neuronal networks established from human induced pluripotent stem cell-derived neural progenitor cells for neurotoxicity evaluation

Neurotoxicity is mediated by a variety of modes-of-actions leading to disturbance of neuronal function. In order to screen larger numbers of compounds for their neurotoxic potential, in vitro functional neuronal networks (NN) might be helpful tools. We established and characterized human NN (hNN) from hiPSC-derived neural progenitor cells by comparing hNN formation with two different differentiation media: in presence (CINDA) and absence (neural differentiation medium (NDM)) of maturation-supporting factors. As a NN control we included differentiating rat NN (rNN) in the study. Gene/protein expression and electrical activity from in vitro developing NN were assessed at multiple time points. Transcriptomes of 5, 14 and 28 days in vitro CINDA-grown hNN were compared to gene expression profiles of in vivo human developing brains. Molecular expression analyses as well as measures of electrical activity indicate that NN mature into neurons of different subtypes and astrocytes over time. In contrast to rNN, hNN are less electrically active within the same period of differentiation time, yet hNN grown in CINDA medium develop higher firing rates than hNN without supplements. Challenge of NN with neuronal receptor stimulators and inhibitors demonstrate presence of inhibitory, GABAergic neurons, whereas glutamatergic responses are limited. hiPSC-derived GABAergic hNN grown in CINDA medium might be a useful tool as part of an in vitro battery for assessing neurotoxicity.

Assessment of developmental neurotoxicity induced by chemical mixtures using an adverse outcome pathway concept

BACKGROUND

In light of the vulnerability of the developing brain, mixture risk assessment (MRA) for the evaluation of developmental neurotoxicity (DNT) should be implemented, since infants and children are co-exposed to more than one chemical at a time. One possible approach to tackle MRA could be to cluster DNT chemicals in a mixture on the basis of their mode of action (MoA) into 'similar' and 'dissimilar', but still contributing to the same adverse outcome, and anchor DNT assays to common key events (CKEs) identified in DNT-specific adverse outcome pathways (AOPs). Moreover, the use of human in vitro models, such as induced pluripotent stem cell (hiPSC)-derived neuronal and glial cultures would enable mechanistic understanding of chemically-induced adverse effects, avoiding species extrapolation.

METHODS

HiPSC-derived neural progenitors differentiated into mixed cultures of neurons and astrocytes were used to assess the effects of acute (3 days) and repeated dose (14 days) treatments with single chemicals and in mixtures belonging to different classes (i.e., lead(II) chloride and methylmercury chloride (heavy metals), chlorpyrifos (pesticide), bisphenol A (organic compound and endocrine disrupter), valproic acid (drug), and PCB138 (persistent organic pollutant and endocrine disrupter), which are associated with cognitive deficits, including learning and memory impairment in children. Selected chemicals were grouped based on their mode of action (MoA) into 'similar' and 'dissimilar' MoA compounds and their effects on synaptogenesis, neurite outgrowth, and brain derived neurotrophic factor (BDNF) protein levels, identified as CKEs in currently available AOPs relevant to DNT, were evaluated by immunocytochemistry and high content imaging analysis.

RESULTS

Chemicals working through similar MoA (i.e., alterations of BDNF levels), at non-cytotoxic (IC20/100), very low toxic (IC5), or moderately toxic (IC20) concentrations, induce DNT effects in mixtures, as shown by increased number of neurons, impairment of neurite outgrowth and synaptogenesis (the most sensitive endpoint as confirmed by mathematical modelling) and increase of BDNF levels, to a certain extent reproducing autism-like cellular changes observed in the brain of autistic children.

CONCLUSIONS

Our findings suggest that the use of human iPSC-derived mixed neuronal/glial cultures applied to a battery of assays anchored to key events of an AOP network represents a valuable approach to identify mixtures of chemicals with potential to cause learning and memory impairment in children.

Nrf2: Redox and Metabolic Regulator of Stem Cell State and Function

Nuclear factor erythroid 2-related factor 2 (Nrf2) is ubiquitously expressed in most eukaryotic cells and functions to induce a broad range of cellular defenses against exogenous and endogenous stresses, including oxidants, xenobiotics, and excessive nutrient/metabolite supply. Because the production and fate of stem cells are often modulated by cellular redox and metabolic homeostasis, important roles of Nrf2 have emerged in the regulation of stem cell quiescence, survival, self-renewal, proliferation, senescence, and differentiation. In a rapidly advancing field, this review summarizes Nrf2 signaling in the context of stem cell state and function and provides a rationale for Nrf2 as a therapeutic target in stem cell-based regenerative medicine.

A novel inhibitor of tumorspheres reveals the activation of the serine biosynthetic pathway upon mitochondrial inhibition

Differences in the metabolism of cancer cells or cancer stem cells (CSCs) as compared to normal cells have provided avenues to safely target cancers. To discover metabolic inhibitors of CSCs, we performed alkaline phosphatase- and tumoursphere-based drug screening using induced cancer stem cell-like cells. From the screening of a RIKEN NPDepo chemical library, we discovered NPD2381 as a novel and selective cancer-stemness inhibitor that targets mitochondrial metabolism. Using our ChemProteoBase profiling, we found that NPD2381 increases the expression of enzymes within the serine biosynthesis pathway. We also found a role for serine in protecting cancer cells from mitochondrial inhibitors. Our results suggest the existence of a compensatory mechanism to increase the level of intracellular serine in response to mitochondrial inhibitors.

Liraglutide and its Neuroprotective Properties-Focus on Possible Biochemical Mechanisms in Alzheimer's Disease and Cerebral Ischemic Events

Liraglutide is a GLP-1 analog (glucagon like peptide-1) used primarily in the treatment of diabetes mellitus type 2 (DM2) and obesity. The literature starts to suggest that liraglutide may reduce the effects of ischemic stroke by activating anti-apoptotic pathways, as well as limiting the harmful effects of free radicals. The GLP-1R expression has been reported in the cerebral cortex, especially occipital and frontal lobes, the hypothalamus, and the thalamus. Liraglutide reduced the area of ischemia caused by MCAO (middle cerebral artery occlusion), limited neurological deficits, decreased hyperglycemia caused by stress, and presented anti-apoptotic effects by increasing the expression of Bcl-2 and Bcl-xl proteins and reduction of Bax and Bad protein expression. The pharmaceutical managed to decrease concentrations of proapoptotic factors, such as NF-κB (Nuclear Factor-kappa β), ICAM-1 (Intercellular Adhesion Molecule 1), caspase-3, and reduced the level of TUNEL-positive cells. Liraglutide was able to reduce the level of free radicals by decreasing the level of malondialdehyde (MDA), and increasing the superoxide dismutase level (SOD), glutathione (GSH), and catalase. Liraglutide may affect the neurovascular unit causing its remodeling, which seems to be crucial for recovery after stroke. Liraglutide may stabilize atherosclerotic plaque, as well as counteract its early formation and further development. Liraglutide, through its binding to GLP-1R (glucagon like peptide-1 receptor) and consequent activation of PI3K/MAPK (Phosphoinositide 3-kinase/mitogen associated protein kinase) dependent pathways, may have a positive impact on Aβ (amyloid beta) trafficking and clearance by increasing the presence of Aβ transporters in cerebrospinal fluid. Liraglutide seems to affect tau pathology. It is possible that liraglutide may have some stem cell stimulating properties. The effects may be connected with PKA (phosphorylase kinase A) activation. This paper presents potential mechanisms of liraglutide activity in conditions connected with neuronal damage, with special emphasis on Alzheimer's disease and cerebral ischemia.

Strategies to improve the regulatory assessment of developmental neurotoxicity (DNT) using in vitro methods

Currently, the identification of chemicals that have the potential to induce developmental neurotoxicity (DNT) is based on animal testing. Since at the regulatory level, systematic testing of DNT is not a standard requirement within the EU or USA chemical legislation safety assessment, DNT testing is only performed in higher tiered testing triggered based on chemical structure activity relationships or evidence of neurotoxicity in systemic acute or repeated dose toxicity studies. However, these triggers are rarely used and, in addition, do not always serve as reliable indicators of DNT, as they are generally based on observations in adult rodents. Therefore, there is a pressing need for developing alternative methodologies that can reliably support identification of DNT triggers, and more rapidly and cost-effectively support the identification and characterization of chemicals with DNT potential. We propose to incorporate mechanistic knowledge and data derived from in vitro studies to support various regulatory applications including: (a) the identification of potential DNT triggers, (b) initial chemical screening and prioritization, (c) hazard identification and characterization, (d) chemical biological grouping, and (e) assessment of exposure to chemical mixtures. Ideally, currently available cellular neuronal/glial models derived from human induced pluripotent stem cells (hiPSCs) should be used as they allow evaluation of chemical impacts on key neurodevelopmental processes, by reproducing different windows of exposure during human brain development. A battery of DNT in vitro test methods derived from hiPSCs could generate valuable mechanistic data, speeding up the evaluation of thousands of compounds present in industrial, agricultural and consumer products that lack safety data on DNT potential.

Recommendation on test readiness criteria for new approach methods in toxicology: Exemplified for developmental neurotoxicity

Multiple non-animal-based test methods have never been formally validated. In order to use such new approach methods (NAMs) in a regulatory context, criteria to define their readiness are necessary. The field of developmental neurotoxicity (DNT) testing is used to exemplify the application of readiness criteria. The costs and number of untested chemicals are overwhelming for in vivo DNT testing. Thus, there is a need for inexpensive, high-throughput NAMs, to obtain initial information on potential hazards, and to allow prioritization for further testing. A background on the regulatory and scientific status of DNT testing is provided showing different types of test readiness levels, depending on the intended use of data from NAMs. Readiness criteria, compiled during a stakeholder workshop, uniting scientists from academia, industry and regulatory authorities are presented. An important step beyond the listing of criteria, was the suggestion for a preliminary scoring scheme. On this basis a (semi)-quantitative analysis process was assembled on test readiness of 17 NAMs with respect to various uses (e.g. prioritization/screening, risk assessment). The scoring results suggest that several assays are currently at high readiness levels. Therefore, suggestions are made on how DNT NAMs may be assembled into an integrated approach to testing and assessment (IATA). In parallel, the testing state in these assays was compiled for more than 1000 compounds. Finally, a vision is presented on how further NAM development may be guided by knowledge of signaling pathways necessary for brain development, DNT pathophysiology, and relevant adverse outcome pathways (AOP).

Liraglutide Activates the Nrf2/HO-1 Antioxidant Pathway and Protects Brain Nerve Cells against Cerebral Ischemia in Diabetic Rats

This study aimed to determine the effect of liraglutide pretreatment and to elucidate the mechanism of nuclear factor erythroid 2-related factor (Nrf2)/heme oxygenase-1 (HO-1) signaling after focal cerebral ischemia injury in diabetic rats model. Adult male Sprague-Dawley rats were randomly divided into the sham-operated (S) group, diabetes mellitus ischemia (DM + MCAO) group, liraglutide pretreatment normal blood glucose ischemia (NDM+MCAO+L) group, and liraglutide pretreatment diabetes ischemia (DM + MCAO + L) group. At 48 h after middle cerebral artery occlusion (MCAO), neurological deficits and infarct volume of brain were measured. Oxidative stress brain tissue was determined by superoxide dismutase (SOD) and myeloperoxidase (MPO) activities. The expression levels of Nrf2 and HO-1 of brain tissue were analyzed by western blotting. In the DM + MCAO + L group, neurological deficits scores and cerebral infarct volume seemed to decrease at 48 h after MCAO cerebral ischemia compared with those in DM + MCAO group (P < 0.05). In addition, the expression of Nrf2 and HO-1 increased in 48 h at liraglutide pretreatment groups after MCAO cerebral ischemia if compared with those in the DM + MCAO group (P < 0.05). Furthermore, the DM + MCAO + L group has no significant difference compared with the NDM + MCAO + L group (P > 0.05). To sum up, alleviating effects of liraglutide on diabetes complicated with cerebral ischemia injury rats would be related to Nrf2/HO-1 signaling pathway.

Rotenone exerts developmental neurotoxicity in a human brain spheroid model

Growing concern suggests that some chemicals exert (developmental) neurotoxicity (DNT and NT) and are linked to the increase in incidence of autism, attention deficit and hyperactivity disorders. The high cost of routine tests for DNT and NT assessment make it difficult to test the high numbers of existing chemicals. Thus, more cost effective neurodevelopmental models are needed. The use of induced pluripotent stem cells (iPSC) in combination with the emerging human 3D tissue culture platforms, present a novel tool to predict and study human toxicity. By combining these technologies, we generated multicellular brain spheroids (BrainSpheres) from human iPSC. The model has previously shown to be reproducible and recapitulates several neurodevelopmental features. Our results indicate, rotenone's toxic potency varies depending on the differentiation status of the cells, showing higher reactive oxygen species (ROS) and higher mitochondrial dysfunction during early than later differentiation stages. Immuno-fluorescence morphology analysis after rotenone exposure indicated dopaminergic-neuron selective toxicity at non-cytotoxic concentrations (1 μM), while astrocytes and other neuronal cell types were affected at (general) cytotoxic concentrations (25 μM). Omics analysis showed changes in key pathways necessary for brain development, indicating rotenone as a developmental neurotoxicant and show a possible link between previously shown effects on neurite outgrowth and presently observed effects on Ca2+ reabsorption, synaptogenesis and PPAR pathway disruption. In conclusion, our BrainSpheres model has shown to be a reproducible and novel tool to study neurotoxicity and developmental neurotoxicity. Results presented here support the idea that rotenone can potentially be a developmental neurotoxicant.

From the Cover: Manganese and Rotenone-Induced Oxidative Stress Signatures Differ in iPSC-Derived Human Dopamine Neurons

Parkinson's disease (PD) is the result of complex interactions between genetic and environmental factors. Two chemically distinct environmental stressors relevant to PD are the metal manganese and the pesticide rotenone. Both are thought to exert neurotoxicity at least in part via oxidative stress resulting from impaired mitochondrial activity. Identifying shared mechanism of action may reveal clues towards an understanding of the mechanisms underlying PD pathogenesis. Here we compare the effects of manganese and rotenone in human-induced pluripotent stem cells-derived postmitotic mesencephalic dopamine neurons by assessing several different oxidative stress endpoints. Manganese, but not rotenone caused a concentration and time-dependent increase in intracellular reactive oxygen/nitrogen species measured by quantifying the fluorescence of oxidized chloromethyl 2',7'-dichlorodihydrofluorescein diacetate (DCF) assay. In contrast, rotenone but not manganese caused an increase in cellular isoprostane levels, an indicator of lipid peroxidation. Manganese and rotenone both caused an initial decrease in cellular reduced glutathione; however, glutathione levels remained low in neurons treated with rotenone for 24 h but recovered in manganese-exposed cells. Neurite length, a sensitive indicator of overall neuronal health was adversely affected by rotenone, but not manganese. Thus, our observations suggest that the cellular oxidative stress evoked by these 2 agents is distinct yielding unique oxidative stress signatures across outcome measures. The protective effect of rasagiline, a compound used in the clinic for PD, had negligible impact on any of oxidative stress outcome measures except a subtle significant decrease in manganese-dependent production of reactive oxygen/nitrogen species detected by the DCF assay.

Protocol for the Differentiation of Human Induced Pluripotent Stem Cells into Mixed Cultures of Neurons and Glia for Neurotoxicity Testing

Human pluripotent stem cells can differentiate into various cell types that can be applied to human-based in vitro toxicity assays. One major advantage is that the reprogramming of somatic cells to produce human induced pluripotent stem cells (hiPSCs) avoids the ethical and legislative issues related to the use of human embryonic stem cells (hESCs). HiPSCs can be expanded and efficiently differentiated into different types of neuronal and glial cells, serving as test systems for toxicity testing and, in particular, for the assessment of different pathways involved in neurotoxicity. This work describes a protocol for the differentiation of hiPSCs into mixed cultures of neuronal and glial cells. The signaling pathways that are regulated and/or activated by neuronal differentiation are defined. This information is critical to the application of the cell model to the new toxicity testing paradigm, in which chemicals are assessed based on their ability to perturb biological pathways. As a proof of concept, rotenone, an inhibitor of mitochondrial respiratory complex I, was used to assess the activation of the Nrf2 signaling pathway, a key regulator of the antioxidant-response-element-(ARE)-driven cellular defense mechanism against oxidative stress.

Adverse outcome pathways: Application to enhance mechanistic understanding of neurotoxicity

Recent developments have prompted the transition of empirically based testing of late stage toxicity in animals for a range of different endpoints including neurotoxicity to more efficient and predictive mechanistically based approaches with greater emphasis on measurable key events early in the progression of disease. The adverse outcome pathway (AOP) has been proposed as a simplified organizational construct to contribute to this transition by linking molecular initiating events and earlier (more predictive) key events at lower levels of biological organization to disease outcomes. As such, AOPs are anticipated to facilitate the compilation of information to increase mechanistic understanding of pathophysiological pathways that are responsible for human disease.

In this review, the sequence of key events resulting in adverse outcome (AO) defined as parkinsonian motor impairment and learning and memory deficit in children, triggered by exposure to environmental chemicals has been briefly described using the AOP framework. These AOPs follow convention adopted in an Organization for Economic Cooperation and Development (OECD) AOP development program, publically available, to permit tailored application of AOPs for a range of different purposes.

Due to the complexity of disease pathways, including neurodegenerative disorders, a specific symptom of the disease (e.g. parkinsonian motor deficit) is considered as the AO in a developed AOP. Though the description is necessarily limited by the extent of current knowledge, additional characterization of involved pathways through description of related AOPs interlinked into networks for the same disease has potential to contribute to more holistic and mechanistic understanding of the pathophysiological pathways involved, possibly leading to the mechanism-based reclassification of diseases, thus facilitating more personalized treatment.