Establishment of Neurotoxicity Assessment Using Microelectrode Array (MEA) with hiPSC-Derived Neurons and Evaluation of New Psychoactive Substances (NPS)

Background and Objectives

Currently, safety pharmacological tests for the central nervous system depend on animal behavioral analysis. However, due to the subjectivity of behavioral analysis and differences between species, there is a limit to appropriate nervous system toxicity assessment, therefore a new neurotoxicity assessment that can simulate the human central nervous system is required.

Methods and Results

In our study, we developed an in vitro neurotoxicity assessment focusing on neuronal function. To minimize the differences between species and fast screening, hiPSC-derived neurons and a microelectrode array (MEA) that could simultaneously measure the action potentials of the neuronal networks were used. After analyzing the molecular and electrophysiological characters of our neuronal network, we conducted a neurotoxicity assessment on neurotransmitters, neurotoxicants, illicit drugs, and new psychoactive substances (NPS). We found that most substances used in our experiments responded more sensitively to our MEA-based neurotoxicity assessment than to the conventional neurotoxicity assessment. Also, this is the first paper that evaluates various illicit drugs and NPS using MEA-based neurotoxicity assessment using hiPSC-derived neurons.

Conclusions

Our study expanded the scope of application of neurotoxicity assessment using hiPSC-derived neurons to NPS, and accumulated evaluation data of various toxic substances for hiPSC-derived neurons.

BAPTA, a calcium chelator, neuroprotects injured neurons in vitro and promotes motor recovery after spinal cord transection in vivo

Aim

Despite animal evidence of a role of calcium in the pathogenesis of spinal cord injury, several studies conducted in the past found calcium blockade ineffective. However, those studies involved oral or parenteral administration of Ca++ antagonists. We hypothesized that Ca++ blockade might be effective with local/immediate application (LIA) at the time of neural injury.

Methods

In this study, we assessed the effects of LIA of BAPTA (1,2‐bis (o‐aminophenoxy) ethane‐N, N, N′, N'‐tetraacetic acid), a cell‐permeable highly selective Ca++ chelator, after spinal cord transection (SCT) in mice over 4 weeks. Effects of BAPTA were assessed behaviorally and with immunohistochemistry. Concurrently, BAPTA was submitted for the first time to multimodality assessment in an in vitro model of neural damage as a possible spinal neuroprotectant.

Results

We demonstrate that BAPTA alleviates neuronal apoptosis caused by physical damage by inhibition of neuronal apoptosis and reactive oxygen species (ROS) generation. This translates to enhanced preservation of electrophysiological function and superior behavioral recovery.

Conclusion

This study shows for the first time that local/immediate application of Ca++ chelator BAPTA is strongly neuroprotective after severe spinal cord injury.

Development and validation of dual-cardiotoxicity evaluation method based on analysis of field potential and contractile force of human iPSC-derived cardiomyocytes / multielectrode assay platform

A recent in vitro cardiovascular safety pharmacology test uses cardiomyocytes derived from human induced pluripotent stem cells (hiPSCs) to overcome the limitations of the classical test systems, such as species differences and local channel analysis. The Comprehensive in vitro Proarrhythmia Assay (CiPA) is a new proarrhythmia screening paradigm proposed by a CiPA steering expert group, which essentially requires iPSCs derived cardiomyocyte-based electrophysiological evaluation technology. Moreover, the measurement of the contractile force is also emerging as an important parameter to recapitulate non-proarrhythmic cardiotoxicity. Therefore, we constructed an multielectrode assay (MEA) evaluation method that can measure the electrophysiological changes with 6 reference drugs in hiPSC-derived cardiomyocytes. Subsequently, it was confirmed that the electrophysiological were changed in accordance with the mechanism of action of the drugs. Furthermore, based on the multi-probe impedance, we confirmed the decrease in contractile force due to treatment with drugs, and developed a platform to evaluate cardiotoxicity according to drugs along with field potential changes. Our excitation-contraction coupling cardiotoxicity assessment is considered to be more supportive in cardiac safety studies on pharmacologic sensitivity by complementing each assessment parameter.

Anti-Inflammatory Effects of M-MSCs in DNCB-Induced Atopic Dermatitis Mice

Atopic dermatitis (AD) is an inflammatory skin disease caused by an imbalance between Th1 and Th2 cells. AD patients suffer from pruritus, excessive dryness, red or inflamed skin, and complications such as sleep disturbances and depression. Although there are currently many AD treatments available there are insufficient data on their long-term stability and comparative effects. Moreover, they have limitations due to various side effects. Multipotent mesenchymal stem cells (M-MSCs) might have potential for next-generation AD therapies. MSCs are capable of immune function regulation and local inflammatory response inhibition. M-MSCs, derived from human embryonic stem cells (hESC), additionally have a stable supply. In L507 antibody array, M-MSCs generally showed similar tendencies to bone marrow-derived mesenchymal stem cells (BM-MSCs), although the immunoregulatory function of M-MSCs seemed to be superior to BM-MSCs. Based on the characteristics of M-MSCs on immunoregulatory functions, we tested a M-MSC conditioned media concentrate (MCMC) in mice with AD lesions on their dorsal skin. MCMC significantly decreased RNA expression levels of inflammatory cytokines in the mouse dorsal skin. It also suppressed serum IgE levels. In addition, significant histopathologic alleviation was identified. In conclusion, secretions of M-MSCs have the potential to effectively improve AD-related inflammatory lesions. M-MSCs showed potential for use in next-generation AD treatment.

Inhibition of BET selectively eliminates undifferentiated pluripotent stem cells

Embryonic stem cells (ESCs) maintain their cellular identity through the systematic regulation of master transcription factors and chromatin remodeling complexes. Recent work has shown that the unusually large-scale enhancers-namely super-enhancers (SEs), on which BRD4, a member of the bromodomain and extraterminal domain (BET) family is highly enriched-could regulate pluripotency-related transcription factors. Moreover, inhibition of BRD4 binding on SEs has been shown to induce the differentiation of ESCs. However, the underlying mechanism of BRD4 inhibition-mediated stem cell differentiation remains elusive. Here we show that both mouse and human ESCs lose their capacity for self-renewal upon treatment with JQ1, a selective inhibitor of BET family including BRD4, with rapid suppression of pluripotency-associated genes. Notably, a high concentration of JQ1 could selectively eliminate ESCs via apoptosis, without affecting the functionality of differentiated somatic cells from ESCs, suggesting that inhibition of BET may have a beneficial effect on the development of pluripotent stem cell-based cell therapy.

Increased expression of bitter taste receptors in human allergic nasal mucosa and their contribution to the shrinkage of human nasal mucosa

OBJECTIVE

Bitter taste receptors (TAS2Rs) are expressed in the extraoral tissues, where they possess various physiological functions. This study is to characterize TAS2Rs expression in normal and allergic nasal mucosa and analyse nasal symptom after challenge with bitter tastes to evaluate their pathophysiological function in normal and allergic nasal mucosa.

METHODS

The expression levels of TAS2Rs (TAS2R4, 5, 7, 10, 14, 39, and 43) in nasal mucosa were investigated by real-time PCR, Western blot, and immunohistochemistry. The expression levels of TAS2Rs and Ca(2+) imaging in cultured epithelial cells were measured after stimulation with type 2 cytokines (IL-4, IL-5, and IL-13) or bitter tastes. Nasal symptoms in control subjects and allergic rhinitis patients using visual analogue score and acoustic rhinometry were evaluated before and after stimulation with bitter tastes. Vascular diameter of rat nasal septum was measured before and after treatment with bitter tastes.

RESULTS

TAS2Rs tested here were expressed in nasal mucosa where they were commonly distributed in superficial epithelium, submucosal glands, and endothelium. Their expression levels are increased in allergic nasal mucosa and up-regulated in cultured epithelial cells simulated with type 2 cytokines. After treatment with bitter tastes, intracellular Ca(2+) signalling was increased in cultured epithelial cells, and vascular constriction was found in rat nasal septum. Increased nasal patency was observed in human nasal mucosa without pain or sneezing.

CONCLUSION AND CLINICAL RELEVANCE

TAS2Rs are constitutively expressed in human nasal mucosa and their expression levels are increased in allergic nasal mucosa, where they could potentially contribute to shrinkage of normal and allergic nasal mucosa.

Posttranslational synthesis of hypusine: evolutionary progression and specificity of the hypusine modification

A naturally occurring unusual amino acid, hypusine [N (epsilon)-(4-amino-2-hydroxybutyl)-lysine] is a component of a single cellular protein, eukaryotic translation initiation factor 5A (eIF5A). It is a modified lysine with structural contribution from the polyamine spermidine. Hypusine is formed in a novel posttranslational modification that involves two enzymes, deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH). eIF5A and deoxyhypusine/hypusine modification are essential for growth of eukaryotic cells. The hypusine synthetic pathway has evolved in eukaryotes and eIF5A, DHS and DOHH are highly conserved, suggesting maintenance of a fundamental cellular function of eIF5A through evolution. The unique feature of the hypusine modification is the strict specificity of the enzymes toward its substrate protein, eIF5A. Moreover, DHS exhibits a narrow specificity toward spermidine. In view of the extraordinary specificity and the requirement for hypusine-containing eIF5A for mammalian cell proliferation, eIF5A and the hypusine biosynthetic enzymes present new potential targets for intervention in aberrant cell proliferation.

Effect of serum and hydrogen peroxide on the Ca2+/calmodulin-dependent phosphorylation of eukaryotic elongation factor 2(eEF-2) in Chinese hamster ovary cells

Eukaryotic elongation factor eEF-2 mediates regulatory steps important for the overall regulation of mRNA translation in mammalian cells and is activated by variety of cellular conditions and factors. In this study, eEF-2 specific, Ca2+/CaM-dependent protein kinase III (CaM PK III), also called eEF-2 kinase, was examined under oxidative stress and cell proliferation state using CHO cells. The eEF-2 kinase activity was determined in the kinase buffer containing Ca2+ and CaM in the presence of eEF-2 and [gamma-32P] ATP. The eEF-2 kinase activity in cell lysates was completely dependent upon Ca2+ and CaM. Phosphorylation of eEF-2 was clearly identified in proliferating cells, but not detectable in CHO cells arrested in their growth by serum deprivation. The content of the eEF-2 protein, however, was equivalent in both cells. Using a phosphorylation state-specific antibody, we show that oxidant such as H2O2, which triggers a large influx of Ca2+, dramatically enhances the phosphorylation of eEF-2. In addition, H2O2-induced eEF-2 phosphorylation is dependent on Ca2+ and CaM, but independent of protein kinase C. In addition, okadaic acid inhibits phosphoprotein phosphatase 2A(PP2A)-mediated eEF-2 dephosphorylation. These results may provide a possible link between the elevation of intracellular Ca2+ and cell division and suggest that phosphorylation of eEF-2 is sensitive cellular reflex on stimuli that induces intracellular Ca2+ flux.

Dietary palm oil alters the lipid stability of polyunsaturated fatty acid-modified poultry products

Laying hens were fed a high polyunsaturated fatty acid (PUFA) diet with three levels [low (LPO, 0%), medium (MPO, 1.5%), and high (HPO, 3.5%)] of palm oil (PO) or a PUFA diet with tocopherol mix (control). Flax and fish oils were used as PUFA sources in all of the diets. Inclusion of tocopherols resulted in a lower (P < 0.05) thiobarbituric acid reactive substances (TBARS) in the control eggs in white and dark meats. Among the PO treatments, eggs from HPO diet had the lowest TBARS (P < 0.05). A higher (P < 0.05) TBARS was observed for eggs, meat, and liver from hens on the LPO diet. No difference was observed between the TBARS of LPO and MPO dark meat. The C22:6 n-3 fatty acid was lower (P < 0.05) in MPO and HPO eggs and the HPO white meat.

Regulation of chicken protein tyrosine phosphatase 1 and human protein tyrosine phosphatase 1B activity by casein kinase II- and p56lck-mediated phosphorylation

Protein tyrosine phosphorylation and dephosphorylation are important in the regulation of cell proliferation and signaling cascade. In order to examine whether phosphatase activity of CPTP1 and HPTP1B, typical nontransmembrane protein tyrosine phosphatase, could be controlled by phosphorylation, affinity-purified PTPs were phosphorylated by CKII and p56lck in vitro. Phosphoamino acid analysis revealed that CPTP1 was phosphorylated on both serine and threonine residues by CKII, and tyrosine residue by p56lck. Phosphatase activity of CPTP1 was gradually increased by three-fold concomitant with phosporylation by CKII. Phosphorylation of HPTP1B by CKII resulted in quick two-fold enhancement of its phosphatase activity within 5 min of incubation and remained in that state. In the presence of CKII inhibitor, heparin or poly(Glu.Tyr), both phosphorylation and enhancement of phosphatase activity of CPTP1 and HPTP1B were mostly blocked. p56lck catalyzed tyrosine phosphorylation of CPTP1 and HPTP1B was only observed by inhibiting the intrinsic tyrosine phosphatase activity. Taken together, these results indicate that CPTP1 or HPTP1B possesses a capability to regulate its phosphatase activity through phosphorylation processes and may participate in the cellular signal cascades.

Characterization of yeast deoxyhypusine synthase: PKC-dependent phosphorylation in vitro and functional domain identification

The biosynthesis of hypusine [Nepsilon-(4-amino-2-hydroxybutyl)-lysine] occurs in the eIF-5A precursor protein through two step posttranslational modification involving deoxyhypusine synthase which catalyzes transfer of the butylamine moiety of spermidine to the epsilon-amino group of a designated lysine residue and subsequent hydroxylation of this intermediate. This enzyme is exclusively required for cell viability and growth of yeast (Park, M.H. et al., J. Biol. Chem. 273: 1677-1683, 1998). In an effort to understand structure-function relationship of deoxyhypusine synthase, posttranslational modification(s) of the enzyme by protein kinases were carried out for a possible cellular modulation of this enzyme. And also twelve deletion mutants were constructed, expressed in E. coli system, and enzyme activities were examined. The results showed that deoxyhypusine synthase was phosphorylated by PKC in vitro but not by p56lck and p60c-src. Treatment with PMA specifically increased the relative phosphorylation of the enzyme supporting PKC was involved. Phosphoamino acid analysis of this enzyme revealed that deoxyhypusine synthase is mostly phosphorylated on serine residue and weakly on threonine. Removal of Met1-Glu10 (deltaMet1-Glu10) residues from amino terminal showed no effect on the catalytic activity but further deletion (deltaMet1-Ser20) caused loss of enzyme activity. The enzyme with internal deletion, deltaGln197-Asn212 (residues not present in the human enzyme) was found to be inactive. Removal of 5 residues from carboxyl terminal, deltaLys383-Asn387, retained only slight activity. These results suggested that deoxyhypusine synthase is substrate for PKC dependent phosphorylation and requires most of the polypeptide chains for enzyme activity except the first 15 residues of N-terminal despite of N- and C-terminal residues of the enzyme consist of variable regions.

Deoxyhypusine synthase activity is essential for cell viability in the yeast Saccharomyces cerevisiae

Deoxyhypusine synthase catalyzes the first step in the posttranslational synthesis of an unusual amino acid, hypusine (N epsilon-(4-amino-2-hydroxybutyl)lysine), in the eukaryotic translation initiation factor 5A (eIF-5A) precursor protein. The null mutation in the single copy gene, yDHS, encoding deoxyhypusine synthase results in the loss of viability in the yeast Saccharomyces cerevisiae. Upon depletion of deoxyhypusine synthase, and consequently of eIF-5A, cessation of growth was accompanied by a marked enlargement of cells, suggesting a defect in cell cycle progression or in cell division. Two residues of the yeast enzyme, Lys308 and Lys350, corresponding to Lys287 and Lys329, respectively, known to be critical for the activity of the human enzyme, were targeted for site-directed mutagenesis. The chromosomal ydhs null mutation was complemented by the plasmid-borne yDHS wild-type gene, but not by mutated genes encoding inactive proteins, including that with Lys350-->Arg substitution or with substitutions at both Lys308 and Lys350. The mutated gene ydhs (K308R) encoding a protein with diminished activities (< 1% of wild type) could support growth but only to a very limited extent. These findings provide strong evidence that the hypusine modification is indeed essential for the survival of S. cerevisiae and imply a vital function for eIF-5A in all eukaryotes.

Identification of YHR068w in Saccharomyces cerevisiae chromosome VIII as a gene for deoxyhypusine synthase. Expression and characterization of the enzyme

Deoxyhypusine synthase catalyzes the formation of deoxyhypusine, the first step in hypusine biosynthesis. Amino acid sequences of five tryptic peptides from rat deoxyhypusine synthase were found to match partially the deduced amino acid sequence of the open reading frame of gene YHR068w of Saccharomyces cerevisiae chromosome VIII (AC:U00061). In order to determine whether the product of this gene corresponds to yeast deoxyhypusine synthase,a 1.17-kilobase pair cDNA with an identical nucleotide sequence to that of the YHR068w coding region was obtained from S. cerevisiae cDNA by polymerase chain reaction and was expressed in Escherichia coli B strain BL21 (DE3). The recombinant protein was found mostly in the E. coli cytosol fraction and comprised approximately 20% of the total soluble protein. The purified form of the expressed protein effectively catalyzed the formation of deoxyhypusine in yeast eIF-5A precursors as well as in human precursor and in those from Chinese hamster ovary cells. The molecular mass of the enzyme was estimated to be 172,000 +/- 4,300 Da by equilibrium centrifugation. The mass of its polypeptide subunit was determined to be approximately 43,000 Da, in close agreement with that calculated for the coding region of the YHRO68w gene. These findings show that this gene is a coding sequence for yeast deoxyhypusine synthase and that the product of this gene exists in a tetrameric form.

Elongation factor-2 in chick embryo is phosphorylated on tyrosine as well as serine and threonine

An endogenous 95 kDa chick embryo cytosolic protein (p95) was phosphorylated in the presence of [gamma-32P]ATP and the kinase activity for p95 was mostly associated with particulate fraction. Phosphorylation of p95 was prominent in embryos of early developmental stage. Hydrolysis of p95 phosphoprotein yielded phosphotyrosine in addition to phosphothreonine and phosphoserine. Native p95 was also tyrosine-phosphorylated. p95 phosphoprotein was purified by DEAE-Sephacel chromatography and immunoprecipitation with anti-phosphotyrosine antibody and the amino acid sequence was determined. The N-terminal sequence, Val-Asn-Phe-Thr-Val-Asp-Gln-Ile-Arg-Ala-Ile-Met-Asp- Lys-Lys-Ala-Asn-Ile-Arg-Asn-Met-, was found to be identical to those of elongation factor-2 (EF-2) of both rat and hamster. Our results suggest the presence of other EF-2 kinase in chick embryo cell than the previously reported Ca2+/calmodulin-dependent protein kinase III.