Emergence of nociceptive functionality and opioid signaling in human induced pluripotent stem cell-derived sensory neurons.

ABSTRACT: Induced pluripotent stem cells (iPSCs) have enabled the generation of various difficult-to-access cell types such as human nociceptors. A key challenge associated with human iPSC-derived nociceptors (hiPSCdNs) is their prolonged functional maturation. While numerous studies have addressed the expression of classic neuronal markers and ion channels in hiPSCdNs, the temporal development of key signaling cascades regulating nociceptor activity has remained largely unexplored. In this study, we used an immunocytochemical high-content imaging approach alongside electrophysiological staging to assess metabotropic and ionotropic signaling of large scale-generated hiPSCdNs across 70 days of in vitro differentiation. During this period, the resting membrane potential became more hyperpolarized, while rheobase, action potential peak amplitude, and membrane capacitance increased. After 70 days, hiPSCdNs exhibited robust physiological responses induced by GABA, pH shift, ATP, and capsaicin. Direct activation of protein kinase A type II (PKA-II) through adenylyl cyclase stimulation with forskolin resulted in PKA-II activation at all time points. Depolarization-induced activation of PKA-II emerged after 35 days of differentiation. However, effective inhibition of forskolin-induced PKA-II activation by opioid receptor agonists required 70 days of in vitro differentiation. Our results identify a pronounced time difference between early expression of functionally important ion channels and emergence of regulatory metabotropic sensitizing and desensitizing signaling only at advanced stages of in vitro cultivation, suggesting an independent regulation of ionotropic and metabotropic signaling. These data are relevant for devising future studies into the development and regulation of human nociceptor function and for defining time windows suitable for hiPSCdN-based drug discovery.

High-content phenotyping of Parkinson's disease patient stem cell-derived midbrain dopaminergic neurons using machine learning classification.

Combining multiple Parkinson's disease (PD) relevant cellular phenotypes might increase the accuracy of midbrain dopaminergic neuron (mDAN) in vitro models. We differentiated patient-derived induced pluripotent stem cells (iPSCs) with a LRRK2 G2019S mutation, isogenic control, and genetically unrelated iPSCs into mDANs. Using automated fluorescence microscopy in 384-well-plate format, we identified elevated levels of α-synuclein (αSyn) and serine 129 phosphorylation, reduced dendritic complexity, and mitochondrial dysfunction. Next, we measured additional image-based phenotypes and used machine learning (ML) to accurately classify mDANs according to their genotype. Additionally, we show that chemical compound treatments, targeting LRRK2 kinase activity or αSyn levels, are detectable when using ML classification based on multiple image-based phenotypes. We validated our approach using a second isogenic patient-derived SNCA gene triplication mDAN model which overexpresses αSyn. This phenotyping and classification strategy improves the practical exploitability of mDANs for disease modeling and the identification of novel LRRK2-associated drug targets.

Dynamics of Metabolic Pathways and Stress Response Patterns during Human Neural Stem Cell Proliferation and Differentiation.

Understanding early nervous system stress response mechanisms is crucial for studying developmental neurotoxicity and devising neuroprotective treatments. We used hiPSC-derived long-term self-renewing neuroepithelial stem (lt-NES) cells differentiated for up to 12 weeks as an in vitro model of human neural development. Following a transcriptome analysis to identify pathway alterations, we induced acute oxidative stress (OS) using tert-butyl hydroperoxide (TBHP) and assessed cell viability at different stages of neural differentiation. We studied NRF2 activation, autophagy, and proteasomal function to explore the contribution and interplay of these pathways in the acute stress response. With increasing differentiation, lt-NES cells showed changes in the expression of metabolic pathway-associated genes with engagement of the pentose phosphate pathway after 6 weeks, this was accompanied by a decreased susceptibility to TBHP-induced stress. Microarray analysis revealed upregulation of target genes of the antioxidant response KEAP1-NRF2-ARE pathway after 6 weeks of differentiation. Pharmacological inhibition of NRF2 confirmed its vital role in the increased resistance to stress. While autophagy was upregulated alongside differentiation, it was not further increased upon oxidative stress and had no effect on stress-induced cell loss and the activation of NRF2 downstream genes. In contrast, proteasome inhibition led to the aggravation of the stress response resulting in decreased cell viability, derangement of NRF2 and KEAP1 protein levels, and lacking NRF2-pathway activation. Our data provide detailed insight into the dynamic regulation and interaction of pathways involved in modulating stress responses across defined time points of neural differentiation.

Deep-learning-based multi-class segmentation for automated, non-invasive routine assessment of human pluripotent stem cell culture status.

Human induced pluripotent stem cells (hiPSCs) are capable of differentiating into a variety of human tissue cells. They offer new opportunities for personalized medicine and drug screening. This requires large quantities of high quality hiPSCs, obtainable only via automated cultivation. One of the major requirements of an automated cultivation is a regular, non-invasive analysis of the cell condition, e.g. by whole-well microscopy. However, despite the urgency of this requirement, there are currently no automatic, image-processing-based solutions for multi-class routine quantification of this nature. This paper describes a method to fully automate the cell state recognition based on phase contrast microscopy and deep-learning. This approach can be used for in process control during an automated hiPSC cultivation. The U-Net based algorithm is capable of segmenting important parameters of hiPSC colony formation and can discriminate between the classes hiPSC colony, single cells, differentiated cells and dead cells. The model achieves more accurate results for the classes hiPSC colonies, differentiated cells, single hiPSCs and dead cells than visual estimation by a skilled expert. Furthermore, parameters for each hiPSC colony are derived directly from the classification result such as roundness, size, center of gravity and inclusions of other cells. These parameters provide localized information about the cell state and enable well based treatment of the cell culture in automated processes. Thus, the model can be exploited for routine, non-invasive image analysis during an automated hiPSC cultivation. This facilitates the generation of high quality hiPSC derived products for biomedical purposes.

Energy Metabolism Disturbances in Cell Models of PARK2 CNV Carriers with ADHD.

The main goal of the present study was the identification of cellular phenotypes in attention-deficit-/hyperactivity disorder (ADHD) patient-derived cellular models from carriers of rare copy number variants (CNVs) in the PARK2 locus that have been previously associated with ADHD. Human-derived fibroblasts (HDF) were cultured and human-induced pluripotent stem cells (hiPSC) were reprogrammed and differentiated into dopaminergic neuronal cells (mDANs). A series of assays in baseline condition and in different stress paradigms (nutrient deprivation, carbonyl cyanide m-chlorophenyl hydrazine (CCCP)) focusing on mitochondrial function and energy metabolism (ATP production, basal oxygen consumption rates, reactive oxygen species (ROS) abundance) were performed and changes in mitochondrial network morphology evaluated. We found changes in PARK2 CNV deletion and duplication carriers with ADHD in PARK2 gene and protein expression, ATP production and basal oxygen consumption rates compared to healthy and ADHD wildtype control cell lines, partly differing between HDF and mDANs and to some extent enhanced in stress paradigms. The generation of ROS was not influenced by the genotype. Our preliminary work suggests an energy impairment in HDF and mDAN cells of PARK2 CNV deletion and duplication carriers with ADHD. The energy impairment could be associated with the role of PARK2 dysregulation in mitochondrial dynamics.

The StemCellFactory: A Modular System Integration for Automated Generation and Expansion of Human Induced Pluripotent Stem Cells.

While human induced pluripotent stem cells (hiPSCs) provide novel prospects for disease-modeling, the high phenotypic variability seen across different lines demands usage of large hiPSC cohorts to decipher the impact of individual genetic variants. Thus, a much higher grade of parallelization, and throughput in the production of hiPSCs is needed, which can only be achieved by implementing automated solutions for cell reprogramming, and hiPSC expansion. Here, we describe the StemCellFactory, an automated, modular platform covering the entire process of hiPSC production, ranging from adult human fibroblast expansion, Sendai virus-based reprogramming to automated isolation, and parallel expansion of hiPSC clones. We have developed a feeder-free, Sendai virus-mediated reprogramming protocol suitable for cell culture processing via a robotic liquid handling unit that delivers footprint-free hiPSCs within 3 weeks with state-of-the-art efficiencies. Evolving hiPSC colonies are automatically detected, harvested, and clonally propagated in 24-well plates. In order to ensure high fidelity performance, we have implemented a high-speed microscope for in-process quality control, and image-based confluence measurements for automated dilution ratio calculation. This confluence-based splitting approach enables parallel, and individual expansion of hiPSCs in 24-well plates or scale-up in 6-well plates across at least 10 passages. Automatically expanded hiPSCs exhibit normal growth characteristics, and show sustained expression of the pluripotency associated stem cell marker TRA-1-60 over at least 5 weeks (10 passages). Our set-up enables automated, user-independent expansion of hiPSCs under fully defined conditions, and could be exploited to generate a large number of hiPSC lines for disease modeling, and drug screening at industrial scale, and quality.

Induced pluripotent stem cell-based modeling of mutant LRRK2-associated Parkinson's disease.

Recent advances in cell reprogramming have enabled assessment of disease-related cellular traits in patient-derived somatic cells, thus providing a versatile platform for disease modeling and drug development. Given the limited access to vital human brain cells, this technology is especially relevant for neurodegenerative disorders such as Parkinson's disease (PD) as a tool to decipher underlying pathomechanisms. Importantly, recent progress in genome-editing technologies has provided an ability to analyze isogenic induced pluripotent stem cell (iPSC) pairs that differ only in a single genetic change, thus allowing a thorough assessment of the molecular and cellular phenotypes that result from monogenetic risk factors. In this review, we summarize the current state of iPSC-based modeling of PD with a focus on leucine-rich repeat kinase 2 (LRRK2), one of the most prominent monogenetic risk factors for PD linked to both familial and idiopathic forms. The LRRK2 protein is a primarily cytosolic multi-domain protein contributing to regulation of several pathways including autophagy, mitochondrial function, vesicle transport, nuclear architecture and cell morphology. We summarize iPSC-based studies that contributed to improving our understanding of the function of LRRK2 and its variants in the context of PD etiopathology. These data, along with results obtained in our own studies, underscore the multifaceted role of LRRK2 in regulating cellular homeostasis on several levels, including proteostasis, mitochondrial dynamics and regulation of the cytoskeleton. Finally, we expound advantages and limitations of reprogramming technologies for disease modeling and drug development and provide an outlook on future challenges and expectations offered by this exciting technology.

Ensuring the Quality of Stem Cell-Derived In Vitro Models for Toxicity Testing.

Quality control of cell cultures used in new in vitro toxicology assays is crucial to the provision of reliable, reproducible and accurate toxicity data on new drugs or constituents of new consumer products. This chapter explores the key scientific and ethical criteria that must be addressed at the earliest stages of developing toxicology assays based on human pluripotent stem cell (hPSC) lines. It also identifies key considerations for such assays to be acceptable for regulatory, laboratory safety and commercial purposes. Also addressed is the development of hPSC-based assays for the tissue and cell types of greatest interest in drug toxicology. The chapter draws on a range of expert opinion within the European Commission/Cosmetics Europe-funded alternative testing cluster SEURAT-1 and consensus from international groups delivering this guidance such as the International Stem Cell Banking Initiative. Accordingly, the chapter summarizes the most up-date best practices in the use and quality control of human Pluripotent Stem Cell lines in the development of in vitro toxicity assays from leading experts in the field.

TDP-43 loss of function inhibits endosomal trafficking and alters trophic signaling in neurons.

Nuclear clearance of TDP-43 into cytoplasmic aggregates is a key driver of neurodegeneration in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), but the mechanisms are unclear. Here, we show that TDP-43 knockdown specifically reduces the number and motility of RAB11-positive recycling endosomes in dendrites, while TDP-43 overexpression has the opposite effect. This is associated with delayed transferrin recycling in TDP-43-knockdown neurons and decreased ß2-transferrin levels in patient CSF Whole proteome quantification identified the upregulation of the ESCRT component VPS4B upon TDP-43 knockdown in neurons. Luciferase reporter assays and chromatin immunoprecipitation suggest that TDP-43 represses VPS4B transcription. Preventing VPS4B upregulation or expression of its functional antagonist ALIX restores trafficking of recycling endosomes. Proteomic analysis revealed the broad reduction in surface expression of key receptors upon TDP-43 knockdown, including ErbB4, the neuregulin 1 receptor. TDP-43 knockdown delays the surface delivery of ErbB4. ErbB4 overexpression, but not neuregulin 1 stimulation, prevents dendrite loss upon TDP-43 knockdown. Thus, impaired recycling of ErbB4 and other receptors to the cell surface may contribute to TDP-43-induced neurodegeneration by blocking trophic signaling.

Impedimetric real-time monitoring of neural pluripotent stem cell differentiation process on microelectrode arrays.

In today's neurodevelopment and -disease research, human neural stem/progenitor cell-derived networks represent the sole accessible in vitro model possessing a primary phenotype. However, cultivation and moreover, differentiation as well as maturation of human neural stem/progenitor cells are very complex and time-consuming processes. Therefore, techniques for the sensitive non-invasive, real-time monitoring of neuronal differentiation and maturation are highly demanded. Using impedance spectroscopy, the differentiation of several human neural stem/progenitor cell lines was analyzed in detail. After development of an optimum microelectrode array for reliable and sensitive long-term monitoring, distinct cell-dependent impedimetric parameters that could specifically be associated with the progress and quality of neuronal differentiation were identified. Cellular impedance changes correlated well with the temporal regulation of biomolecular progenitor versus mature neural marker expression as well as cellular structure changes accompanying neuronal differentiation. More strikingly, the capability of the impedimetric differentiation monitoring system for the use as a screening tool was demonstrated by applying compounds that are known to promote neuronal differentiation such as the γ-secretase inhibitor DAPT. The non-invasive impedance spectroscopy-based measurement system can be used for sensitive and quantitative monitoring of neuronal differentiation processes. Therefore, this technique could be a very useful tool for quality control of neuronal differentiation and moreover, for neurogenic compound identification and industrial high-content screening demands in the field of safety assessment as well as drug development.

Neural commitment of human pluripotent stem cells under defined conditions recapitulates neural development and generates patient-specific neural cells.

Standardization of culture methods for human pluripotent stem cell (PSC) neural differentiation can greatly contribute to the development of novel clinical advancements through the comprehension of neurodevelopmental diseases. Here, we report an approach that reproduces neural commitment from human induced pluripotent stem cells using dual-SMAD inhibition under defined conditions in a vitronectin-based monolayer system. By employing this method it was possible to obtain neurons derived from both control and Rett syndrome patients' pluripotent cells. During differentiation mutated cells displayed alterations in the number of neuronal projections, and production of Tuj1 and MAP2-positive neurons. Although investigation of a broader number of patients would be required, these observations are in accordance with previous studies showing impaired differentiation of these cells. Consequently, our experimental methodology was proved useful not only for the generation of neural cells, but also made possible to compare neural differentiation behavior of different cell lines under defined culture conditions. This study thus expects to contribute with an optimized approach to study the neural commitment of human PSCs, and to produce patient-specific neural cells that can be used to gain a better understanding of disease mechanisms.

A reproducible and versatile system for the dynamic expansion of human pluripotent stem cells in suspension.

Reprogramming of patient cells to human induced pluripotent stem cells (hiPSC) has facilitated in vitro disease modeling studies aiming at deciphering the molecular and cellular mechanisms that contribute to disease pathogenesis and progression. To fully exploit the potential of hiPSC for biomedical applications, technologies that enable the standardized generation and expansion of hiPSC from large numbers of donors are required. Paralleled automated processes for the expansion of hiPSC could provide an opportunity to maximize the generation of hiPSC collections from patient cohorts while minimizing hands-on time and costs. In order to develop a simple method for the parallel expansion of human pluripotent stem cells (hPSC) we established a protocol for their cultivation as undifferentiated aggregates in a bench-top bioreactor system (BioLevitator™). We show that long-term expansion (10 passages) of hPSCs either in mTeSR or E8 medium preserved a normal karyotype, three-germ-layer differentiation potential and high expression of pluripotency-associated markers. The system enables the expansion from low inoculation densities (0.3 × 10(5) cells/mL) and provides a simplified, cost-efficient and time-saving method for the provision of hiPSC at midi-scale. Implementation of this protocol in cell production schemes has the potential to advance cell manufacturing in many areas of hiPSC-based medical research.

Spatial and temporal control of cell aggregation efficiently directs human pluripotent stem cells towards neural commitment.

3D suspension culture is generally considered a promising method to achieve efficient expansion and controlled differentiation of human pluripotent stem cells (hPSCs). In this work, we focused on developing an integrated culture platform for expansion and neural commitment of hPSCs into neural precursors using 3D suspension conditions and chemically-defined culture media. We evaluated different inoculation methodologies for hPSC expansion as 3D aggregates and characterized the resulting cultures in terms of aggregate size distribution. It was demonstrated that upon single-cell inoculation, after four days of culture, 3D aggregates were composed of homogenous populations of hPSC and were characterized by an average diameter of 139 ± 26 µm, which was determined to be the optimal size to initiate neural commitment. Temporal analysis revealed that upon neural specification it is possible to maximize the percentage of neural precursor cells expressing the neural markers Sox1 and Pax6 after nine days of culture. These results highlight our ability to define a robust method for production of hPSC-derived neural precursors that minimizes processing steps and that constitutes a promising alternative to the traditional planar adherent culture system due to a high potential for scaling-up.

Integrated platform for production and purification of human pluripotent stem cell-derived neural precursors.

Human pluripotent stem cells (hPSCs) are a promising source of cells for clinical applications, such as transplantation of clinically engineered tissues and organs, and drug discovery programs due to their ability to self-renew and to be differentiated into cells from the three embryonic germ layers. In this study, the differentiation of two hPSC-lines into neural precursors (NPs) was accomplished with more than 80% efficiency, by means of the dual-SMAD inhibition protocol, based on the use of two small molecules (SB431542 and LDN193189) to generate Pax6 and Nestin-positive neural entities. One of the major hurdles related to the in vitro generation of PSC-derived populations is the tumorigenic potential of cells that remain undifferentiated. These remaining hPSCs have the potential to generate teratomas after being transplanted, and may interfere with the outcome of in vitro differentiation protocols. One strategy to tackle this problem is to deplete these "contaminating" cells during the differentiation process. Magnetic activated cell sorting (MACS) was used for the first time for purification of hPSC-derived NPs after the neural commitment stage using anti-Tra-1-60 micro beads for negative selection of the unwanted hPSCs. The depletion had an average efficiency of 80.4 ± 5% and less than 1.5% of Tra-1-60 positive cells were present in the purified populations. After re-plating, the purified neural precursors maintained their phenotype, and the success of the preparative purification with MACS was further confirmed with a decrease of 94.3% in the number of Oct4-positive proliferating hPSC colonies. Thus, the integration of the MACS depletion step with the neural commitment protocol paves the way towards the establishment of a novel bioprocess for production of purified populations of hPSC-derived neural cells for different applications.

Non-genetic modulation of Notch activity by artificial delivery of Notch intracellular domain into neural stem cells.

Stem cells have become a major focus of scientific interest as a potential source of somatic cell types for biomedical applications. Understanding and controlling the elicitors and mechanisms in differentiation of pluripotent stem cell-derived somatic cell types remains a key challenge. The major types of molecular processes that control cellular differentiation involve evolutionary conserved cell signaling pathways. Notch receptors participate in a wide variety of biological processes, including cell fate decisions of stem cells. This study explores the potential of protein transduction to directly deliver recombinant Notch-1 intracellular domain (NICD) into mammalian cells in order to accomplish transgene-free Notch activation. We engineered a cell-permeant version of NICD and explored its function on mouse and human neural stem cells. We show that NICD transduction modulates known direct and indirect Notch target genes and antagonizes the DAPT-mediated inhibition of Notch signaling on the transcriptional level. Moreover, NICD enhances cell proliferation accompanied by increased cyclin D1 and decreased p27 protein levels. In the absence of growth factors NICD strongly impairs neuronal differentiation while being insufficient to keep cells in a proliferative state. Furthermore, our studies depict NICD protein transduction as a novel tool for a time and dose-dependent non-genetic modulation of Notch signaling to decipher its cellular functions.

Automated selection and harvesting of pluripotent stem cell colonies.

The ability of pluripotent stem cells to differentiate into specialized cells of all three germ layers, their capability to self-renew, and their amenability to genetic modification provide fascinating prospects for the generation of cell lines for biomedical applications. Therefore, stem cells must increasingly suffice in terms of industrial standards, and automation of critical or time-consuming steps becomes a fundamental prerequisite for their routine application. Cumbersome manual picking of individual stem cell colonies still represents the most frequently used method for passaging or derivation of clonal stem cell lines. Here, we explore an automated harvesting system (CellCelector™) for detection, isolation, and propagation of human embryonic stem cells (hESCs) and murine induced pluripotent stem cells (iPSCs). Automatically transferred hESC colonies maintained their specific biological characteristics even after repeated passaging. We also selected and harvested primary iPSCs derived from mouse embryonic fibroblasts expressing the green fluorescent protein (GFP) under the control of the Oct4 promotor using either morphological criteria or GFP fluorescence. About 80% of the selected and harvested primary iPSC colonies gave rise to homogenously GFP-expressing iPSC lines. To validate the iPSC lines, we analyzed the expression of pluripotency-associated markers and multi-germ layer differentiation potential in vitro. Our data indicate that the CellCelector™ technology enables efficient identification and isolation of pluripotent stem cell colonies at the phase contrast or fluorescence level.

Inhibition of notch signaling in human embryonic stem cell-derived neural stem cells delays G1/S phase transition and accelerates neuronal differentiation in vitro and in vivo.

The controlled in vitro differentiation of human embryonic stem cells (hESCs) and other pluripotent stem cells provides interesting prospects for generating large numbers of human neurons for a variety of biomedical applications. A major bottleneck associated with this approach is the long time required for hESC-derived neural cells to give rise to mature neuronal progeny. In the developing vertebrate nervous system, Notch signaling represents a key regulator of neural stem cell (NSC) maintenance. Here, we set out to explore whether this signaling pathway can be exploited to modulate the differentiation of hESC-derived NSCs (hESNSCs). We assessed the expression of Notch pathway components in hESNSCs and demonstrate that Notch signaling is active under self-renewing culture conditions. Inhibition of Notch activity by the gamma-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT) in hESNSCs affects the expression of human homologues of known targets of Notch and of several cell cycle regulators. Furthermore, DAPT-mediated Notch inhibition delays G1/S-phase transition and commits hESNSCs to neurogenesis. Combined with growth factor withdrawal, inhibition of Notch signaling results in a marked acceleration of differentiation, thereby shortening the time required for the generation of electrophysiologically active hESNSC-derived neurons. This effect can be exploited for neural cell transplantation, where transient Notch inhibition before grafting suffices to promote the onset of neuronal differentiation of hESNSCs in the host tissue. Thus, interference with Notch signaling provides a tool for controlling human NSC differentiation both in vitro and in vivo.

Laser-assisted photoablation of human pluripotent stem cells from differentiating cultures.

Due to their pluripotency and their self-renewal capacity, human pluripotent stem cells (hPSC) provide fascinating perspectives for biomedical applications. In the long term, hPSC-derived tissue-specific cells will constitute an important source for cell replacement therapies in non-regenerative organs. These therapeutic approaches, however, will critically depend on the purity of the in vitro differentiated cell populations. In particular, remaining undifferentiated hPSC in a transplant can induce teratoma formation. In order to address this challenge, we have developed a laser-based method for the ablation of hPSC from differentiating cell cultures. Specific antibodies were directed against the hPSC surface markers tumor related antigen (Tra)-1-60 and Tra-1-81. These antibodies, in turn, were targeted with nanogold particles. Subsequent laser exposure resulted in a 98,9 +/- 0,9% elimination of hPSCs within undifferentiated cell cultures. In order to study potential side effects of laser ablation on cells negative for Tra-1-60 and Tra-1-81, hPSC were mixed with GFP-positive hPSC-derived neural precursors (hESCNP) prior to ablation. These studies showed efficient elimination of hPSC while co-treated hESCNP maintained their normal proliferation and differentiation potential. In vivo transplantation of treated and untreated mixed hPSC/hESCNP cultures revealed that laser ablation can dramatically reduce the risk of teratoma formation. Laser-assisted photothermolysis thus represents a novel contact-free method for the efficient elimination of hPSC from in vitro differentiated hPSC-derived somatic cell populations.

Defining maximum levels of higher alcohols in alcoholic beverages and surrogate alcohol products.

Higher alcohols occur naturally in alcoholic beverages as by-products of alcoholic fermentation. Recently, concerns have been raised about the levels of higher alcohols in surrogate alcohol (i.e., illicit or home-produced alcoholic beverages) that might lead to an increased incidence of liver diseases in regions where there is a high consumption of such beverages. In contrast, higher alcohols are generally regarded as important flavour compounds, so that European legislation even demands minimum contents in certain spirits. In the current study we review the scientific literature on the toxicity of higher alcohols and estimate tolerable concentrations in alcoholic beverages. On the assumption that an adult consumes 4 x 25 ml of a drink containing 40% vol alcohol, the maximum tolerable concentrations of 1-propanol, 1-butanol, 2-butanol, isobutanol, isoamyl alcohol and 1-hexanol in such a drink would range between 228 and 3325 g/hl of pure alcohol. A reasonable preliminary guideline level would be 1000 g/hl of pure alcohol for the sum of all higher alcohols. This level is higher than the concentrations usually found in both legal alcoholic beverages and surrogate alcohols, so that we conclude that scientific data are lacking so far to consider higher alcohols as a likely cause for the adverse effects of surrogate alcohol. The limitations of our study include the inadequate toxicological data base leading to uncertainties during the extrapolation of toxicological data between the different alcohols, as well as unknown interactions between the different higher alcohols and ethanol.

Stage-specific conditional mutagenesis in mouse embryonic stem cell-derived neural cells and postmitotic neurons by direct delivery of biologically active Cre recombinase.

Conditional mutagenesis using Cre/loxP recombination is a powerful tool to investigate genes involved in neural development and function. However, the efficient delivery of biologically active Cre recombinase to neural cells, particularly to postmitotic neurons, represents a limiting factor. In this study, we devised a protocol enabling highly efficient conditional mutagenesis in ESC-derived neural progeny. Using a stepwise in vitro differentiation paradigm, we demonstrate that recombinant cell-permeable Cre protein can be used to efficiently induce recombination at defined stages of neural differentiation. Recombination rates of more than 90% were achieved in multipotent pan-neural and glial precursors derived from the Z/EG reporter mouse ESC line, in which Cre recombination activates enhanced green fluorescent proteinexpression. Recombined precursor cells displayed a normal phenotype and were able to differentiate into neurons and/or glial cells, indicating that Cre treatment has no overt side effects on proliferation and neural differentiation. Our data further demonstrate that recombination via Cre protein transduction is not restricted to dividing cells but can even be applied to postmitotic neurons. The ability to conduct Cre/loxP recombination at defined stages of stem cell differentiation in an expression-independent manner provides new prospects for studying the role of individual genes under stringent temporal control.