Cytoprotective effects of Hangekobokuto against corticosterone-induced cell death in HT22 cells

The hypothalamic-pituitary-adrenal (HPA) system plays an important role in stress response. Chronic stress is thought to induce neuronal damage and contribute to the pathogenesis of psychiatric disorders by causing dysfunction of the HPA system and promoting the production and release of glucocorticoids, including corticosterone and cortisol. Several clinical studies have demonstrated the efficacy of herbal medicines in treating psychiatric disorders; however, their effects on corticosterone-induced neuronal cell death remain unclear. Here, we used HT22 cells to evaluate the neuroprotective potential of herbal medicines used in neuropsychiatry against corticosterone-induced hippocampal neuronal cell death. Cell death was assessed using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) reduction and Live/Dead assays. Hangekobokuto, Kamikihito, Saikokaryukotsuboreito, Kamishoyosan, and Yokukansan were supplied in the form of water-extracted dried powders. Exposure of HT22 cells to ≥ 100 μM corticosterone decreased MTT values. Exposure to 500 μM corticosterone alone reduced MTT values to 18%, while exposure to 10 μM Mifepristone (RU486)-a glucocorticoid receptor antagonist-restored values to 36%. Corticosterone-induced cell death was partially suppressed by treatment with RU486. At 100 μg/mL, Hangekobokuto significantly suppressed the decrease in MTT values (15-32%) and increase in the percentage of ethidium homodimer-1-positive dead cells caused by corticosterone exposure (78-36%), indicating an inhibitory effect on cell death. By contrast, Kamikihito, Saikokaryukotsuboreito, Kamishoyosan, and Yokukansan did not affect corticosterone-induced cell death. Therefore, our results suggest that Hangekobokuto may ameliorate the onset and progression of psychiatric disorders by suppressing neurological disorders associated with increased levels of glucocorticoids.

Therapeutic effect of aged garlic extract on gingivitis in dogs

Periodontal disease is one of the most common dental health problems in dogs. Clinical studies in humans have shown that aged garlic extract (AGE), which contains stable and water-soluble sulfur-containing bioactive compounds, improves the symptoms of periodontal diseases. Our previous study demonstrated that oral administration of AGE in healthy Beagle dogs at 90 mg/kg/day for 12 weeks had no adverse effects such as hemolytic anemia, which is well known to occur as a result of ingestion of Allium species, including onions and garlic, in dogs. However, the therapeutic potential of AGE in canine periodontal disease remains unclear. Accordingly, we investigated the therapeutic effects of AGE in Beagle dogs with mild gingivitis. Feeding 18 mg/kg/day of AGE for 8 weeks resulted in the improvement of gingival index score, level of volatile sulfur compounds in exhaled air, and enzyme activity of periodontal pathogens without any adverse effects on clinical signs and hematological and serum biochemical parameters. Moreover, AGE increased the concentration of salivary cathelicidin, an antimicrobial peptide that contributes to the oral innate immune response. These results suggest that AGE could be a potential therapeutic agent for canine gingivitis.

Anti-Inflammatory Effects of Miyako Bidens pilosa in a Mouse Model of Amyotrophic Lateral Sclerosis and Lipopolysaccharide-Stimulated BV-2 Microglia

Neuroinflammation is a fundamental feature in the pathogenesis of amyotrophic lateral sclerosis (ALS) and arises from the activation of astrocytes and microglial cells. Previously, we reported that Miyako Bidens pilosa extract (MBP) inhibited microglial activation and prolonged the life span in a human ALS-linked mutant superoxide dismutase-1 (SOD1G93A) transgenic mouse model of ALS (G93A mice). Herein, we evaluated the effect of MBP on microglial activation in the spinal cord of G93A mice and lipopolysaccharide-stimulated BV-2 microglial cells. The administration of MBP inhibited the upregulation of the M1-microglia/macrophage marker (interferon-γ receptor (IFN-γR)) and pro-inflammatory cytokines (tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6) in G93A mice. However, MBP did not affect the increase in the M2-microglia/macrophage marker (IL-13R) and anti-inflammatory cytokines (transforming growth factor (TGF)-β and IL-10) in G93A mice. BV-2 cell exposure to MBP resulted in a decrease in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) reduction activity and bromodeoxyuridine incorporation, without an increase in the number of ethidium homodimer-1-stained dead cells. Moreover, MBP suppressed the production of lipopolysaccharide-induced pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) in BV-2 cells. These results suggest that the selective suppression of M1-related pro-inflammatory cytokines is involved in the therapeutic potential of MBP in ALS model mice.

Update on the pathological roles of prostaglandin E2 in neurodegeneration in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by selective degeneration of upper and lower motor neurons. The pathogenesis of ALS remains largely unknown; however, inflammation of the spinal cord is a focus of ALS research and an important pathogenic process in ALS. Prostaglandin E₂ (PGE₂) is a major lipid mediator generated by the arachidonic-acid cascade and is abundant at inflammatory sites. PGE₂ levels are increased in the postmortem spinal cords of ALS patients and in ALS model mice. Beneficial therapeutic effects have been obtained in ALS model mice using cyclooxygenase-2 inhibitors to inhibit the biosynthesis of PGE₂, but the usefulness of this inhibitor has not yet been proven in clinical trials. In this review, we present current evidence on the involvement of PGE₂ in the progression of ALS and discuss the potential of microsomal prostaglandin E synthase (mPGES) and the prostaglandin receptor E-prostanoid (EP) 2 as therapeutic targets for ALS. Signaling pathways involving prostaglandin receptors mediate toxic effects in the central nervous system. In some situations, however, the receptors mediate neuroprotective effects. Our recent studies demonstrated that levels of mPGES-1, which catalyzes the final step of PGE₂ biosynthesis, are increased at the early-symptomatic stage in the spinal cords of transgenic ALS model mice carrying the G93A variant of superoxide dismutase-1. In addition, in an experimental motor-neuron model used in studies of ALS, PGE₂ induces the production of reactive oxygen species and subsequent caspase-3-dependent cytotoxicity through activation of the EP2 receptor. Moreover, this PGE₂-induced EP2 up-regulation in motor neurons plays a role in the death of motor neurons in ALS model mice. Further understanding of the pathophysiological role of PGE₂ in neurodegeneration may provide new insights to guide the development of novel therapies for ALS.

S-1-propenyl-L-cysteine suppresses lipopolysaccharide-induced expression of matrix metalloproteinase-1 through inhibition of tumor necrosis factor-α converting enzyme-epidermal growth factor receptor axis in human gingival fibroblasts

Periodontal disease is the most common dental health problem characterized by the destruction of connective tissue and the resorption of alveolar bone resulting from a chronic infection associated with pathogenic bacteria in the gingiva. Aged garlic extract has been reported to improve gingival bleeding index and probing pocket depth score in patients with mild to moderate periodontitis. Although our previous study found that aged garlic extract and its constituents suppressed the tumor necrosis factor-α-induced inflammatory responses in a human gingival epithelial cell line, the mechanism underlying the effect of aged garlic extract on the destruction of the gingiva remains unclear. The present study investigated the effect of S-1-propenyl-L-cysteine, one of the major sulfur bioactive compounds in aged garlic extract, on the lipopolysaccharide-induced expression of matrix metalloproteinases in human gingival fibroblasts HGF-1 cells. Matrix metalloproteinases are well known to be closely related to the destruction of the gingiva. We found that S-1-propenyl-L-cysteine suppressed the lipopolysaccharide-induced expression and secretion of matrix metalloproteinase-1 in HGF-1 cells. In addition, S-1-propenyl-L-cysteine inhibited the lipopolysaccharide-induced phosphorylation of epidermal growth factor receptor and expression of the active form of tumor necrosis factor-α converting enzyme. Furthermore, the inhibitors of epidermal growth factor receptor tyrosine kinase and tumor necrosis factor-α converting enzyme, AG-1478 and TAPI-1, respectively, reduced the lipopolysaccharide-induced protein level of matrix metalloproteinase-1, as did S-1-propenyl-L-cysteine. Taken together, these results suggested that S-1-propenyl-L-cysteine suppresses the lipopolysaccharide-induced expression of matrix metalloproteinase-1 through the blockade of the tumor necrosis factor-α converting enzyme-epidermal growth factor receptor axis in gingival fibroblasts.

Present State and Future Perspectives of Prostaglandins as a Differentiation Factor in Motor Neurons

Spinal motor neurons have the longest axons that innervate the skeletal muscles of the central nervous system. Motor neuron diseases caused by spinal motor neuron cell death are incurable due to the unique and irreplaceable nature of their neural circuits. Understanding the mechanisms of neurogenesis, neuritogenesis, and synaptogenesis in motor neurons will allow investigators to develop new in vitro models and regenerative therapies for motor neuron diseases. In particular, small molecules can directly reprogram and convert into neural stem cells and neurons, and promote neuron-like cell differentiation. Prostaglandins are known to have a role in the differentiation and tissue regeneration of several cell types and organs. However, the involvement of prostaglandins in the differentiation of motor neurons from neural stem cells is poorly understood. The general cell line used in research on motor neuron diseases is the mouse neuroblastoma and spinal motor neuron fusion cell line NSC-34. Recently, our laboratory reported that prostaglandin E₂ and prostaglandin D₂ enhanced the conversion of NSC-34 cells into motor neuron-like cells with neurite outgrowth. Moreover, we found that prostaglandin E₂-differentiated NSC-34 cells had physiological and electrophysiological properties of mature motor neurons. In this review article, we provide contemporary evidence on the effects of prostaglandins, particularly prostaglandin E₂ and prostaglandin D₂, on differentiation and neural conversion. We also discuss the potential of prostaglandins as candidates for the development of new therapeutic drugs for motor neuron diseases.

Highly Efficient Conversion of Motor Neuron-Like NSC-34 Cells into Functional Motor Neurons by Prostaglandin E2

Motor neuron diseases are a group of progressive neurological disorders that degenerate motor neurons. The neuroblastoma × spinal cord hybrid cell line NSC-34 is widely used as an experimental model in studies of motor neuron diseases. However, the differentiation efficiency of NSC-34 cells to neurons is not always sufficient. We have found that prostaglandin E₂ (PGE₂) induces morphological differentiation in NSC-34 cells. The present study investigated the functional properties of PGE₂-differentiated NSC-34 cells. Retinoic acid (RA), a widely-used agent inducing cell differentiation, facilitated neuritogenesis, which peaked on day 7, whereas PGE₂-induced neuritogenesis took only 2 days to reach the same level. Whole-cell patch-clamp recordings showed that the current threshold of PGE₂-treated cell action potentials was lower than that of RA-treated cells. PGE₂ and RA increased the protein expression levels of neuronal differentiation markers, microtubule-associated protein 2c and synaptophysin, and to the same extent, motor neuron-specific markers HB9 and Islet-1. On the other hand, protein levels of choline acetyltransferase and basal release of acetylcholine in PGE₂-treated cells were higher than in RA-treated cells. These results suggest that PGE₂ is a rapid and efficient differentiation-inducing factor for the preparation of functionally mature motor neurons from NSC-34 cells.

The Molecular Mechanisms Underlying Prostaglandin D2-Induced Neuritogenesis in Motor Neuron-Like NSC-34 Cells

Prostaglandins are a group of physiologically active lipid compounds derived from arachidonic acid. Our previous study has found that prostaglandin E2 promotes neurite outgrowth in NSC-34 cells, which are a model for motor neuron development. However, the effects of other prostaglandins on neuronal differentiation are poorly understood. The present study investigated the effect of prostaglandin D2 (PGD2) on neuritogenesis in NSC-34 cells. Exposure to PGD2 resulted in increased percentages of neurite-bearing cells and neurite length. Although D-prostanoid receptor (DP) 1 and DP2 were dominantly expressed in the cells, BW245C (a DP1 agonist) and 15(R)-15-methyl PGD2 (a DP2 agonist) had no effect on neurite outgrowth. Enzyme-linked immunosorbent assay demonstrated that PGD2 was converted to 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) under cell-free conditions. Exogenously applied 15d-PGJ2 mimicked the effect of PGD2 on neurite outgrowth. GW9662, a peroxisome proliferator-activated receptor-gamma (PPARγ) antagonist, suppressed PGD2-induced neurite outgrowth. Moreover, PGD2 and 15d-PGJ2 increased the protein expression of Islet-1 (the earliest marker of developing motor neurons), and these increases were suppressed by co-treatment with GW9662. These results suggest that PGD2 induces neuritogenesis in NSC-34 cells and that PGD2-induced neurite outgrowth was mediated by the activation of PPARγ through the metabolite 15d-PGJ2.

Pathophysiological role of prostaglandin E2-induced up-regulation of the EP2 receptor in motor neuron-like NSC-34 cells and lumbar motor neurons in ALS model mice

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by selective degeneration of motor neurons. The primary triggers for motor neuronal death are still unknown, but inflammation is considered to be an important factor contributing to the pathophysiology of ALS both clinically and in ALS models. Prostaglandin E2 (PGE2) and its corresponding four E-prostanoid receptors play a pivotal role in the degeneration of motor neurons in human and transgenic models of ALS. It has also been shown that PGE2-EP2 signaling in glial cells (astrocytes or microglia) promotes motor neuronal death in G93A mice. The present study was designed to investigate the levels of expression of EP receptors in the spinal motor neurons of ALS model mice and to examine whether PGE2 alters the expression of EP receptors in differentiated NSC-34 cells, a motor neuron-like cell line. Immunohistochemical staining demonstrated that EP2 and EP3 immunoreactivity was localized in NeuN-positive large cells showing the typical morphology of motor neurons in mice. Semi-quantitative analysis showed that the immunoreactivity of EP2 in motor neurons was significantly increased in the early symptomatic stage in ALS model mice. In contrast, the level of EP3 expression remained constant, irrespective of age. In differentiated NSC-34 cells, bath application of PGE2 resulted in a concentration-dependent decrease of MTT reduction. Although PGE2 had no effect on cell survival at concentrations of less than 10 μM, pretreatment with 10 μM PGE2 significantly up-regulated EP2 and concomitantly potentiated cell death induced by 30 μM PGE2. These results suggest that PGE2 is an important effector for induction of the EP2 subtype in differentiated NSC-34 cells, and that not only EP2 up-regulation in glial cells but also EP2 up-regulation in motor neurons plays a pivotal role in the vulnerability of motor neurons in ALS model mice.

Increased Expression of 15-Hydroxyprostaglandin Dehydrogenase in Spinal Astrocytes During Disease Progression in a Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset, progressive, and fatal neurodegenerative disease caused by selective loss of motor neurons. Both ALS model mice and patients with sporadic ALS have increased levels of prostaglandin E2 (PGE2). Furthermore, the protein levels of microsomal PGE synthase-1 and cyclooxygenase-2, which catalyze PGE2 biosynthesis, are significantly increased in the spinal cord of ALS model mice. However, it is unclear whether PGE2 metabolism in the spinal cord is altered. In the present study, we investigated the protein level of 15-hydroxyprostaglandin dehydrogenase (15-PGDH), a key enzyme in prostaglandin metabolism, in ALS model mice at three different disease stages. Western blotting revealed that the 15-PGDH level was significantly increased in the lumbar spinal cord at the symptomatic stage and end stage. Immunohistochemical staining demonstrated that 15-PGDH immunoreactivity was localized in glial fibrillary acidic protein (GFAP)-positive astrocytes at the end stage. In contrast, 15-PGDH immunoreactivity was not identified in NeuN-positive large cells showing the typical morphology of motor neurons in the anterior horn. Unlike 15-PGDH, the level of PGE2 in the spinal cord was increased only at the end stage. These results suggest that the significant increase of PGE2 at the end stage of ALS in this mouse model is attributable to an imbalance of the synthetic pathway and 15-PGDH-dependent scavenging system for PGE2, and that this drives the pathogenetic mechanism responsible for transition from the symptomatic stage.