Yoshimitsu Kiriyama

Troglitazone suppresses cell growth of KU812 cells independently of PPARγ

We examined the effects of troglitazone, one of thiazolidinedione derivatives on human basophilic leukemia cell line KU812. Troglitazone caused the suppression of cell growth, which was suggested to result from the decrease in cyclin E and the hyperphosphorylated form of retinoblastoma tumor suppressor gene product (pRb). In addition, troglitazone caused a decrease in histamine secretion due to the reduced expression of histidine decarboxylase mRNA. Peroxisome proliferator-activated receptor (PPAR)-gamma mRNA was undetectable by reverse transcription-polymerase chain reaction (RT-PCR) in KU812 cells. These findings suggested that troglitazone suppressed cell growth and histamine synthesis independently of PPARgamma.

The Function of Autophagy in Neurodegenerative Diseases.

Macroautophagy, hereafter referred to as autophagy, is a bulk degradation process performed by lysosomes in which aggregated and altered proteins as well as dysfunctional organelles are decomposed. Autophagy is a basic cellular process that maintains homeostasis and is crucial for postmitotic neurons. Thus, impaired autophagic processes in neurons lead to improper homeostasis and neurodegeneration. Recent studies have suggested that impairments of the autophagic process are associated with several neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and static encephalopathy of childhood with neurodegeneration in adulthood. In this review, we focus on the recent findings regarding the autophagic process and the involvement of autophagy in neurodegenerative diseases.

Protein kinase A-dependent IL-6 production induced by calcitonin in human glioblastoma A172 cells.

In human glioblastoma A172 cells, interleukin-6 (IL-6) production was induced by interleukin-1 beta (IL-1 beta) and dibutyryl cyclic AMP. These cells have been shown to induce IL-6 production via a cAMP-protein kinase A system. Since calcitonin (CT) and calcitonin gene-related peptide (CGRP) are known to increase cAMP accumulation in murine and rat astrocytes, we examined whether these neuropeptides induced IL-6 production in A172 cells. Human CT and human CGRP increased IL-6 production and cAMP accumulation in a dose-dependent manner. A specific protein kinase A inhibitor, H-89, inhibited both CT- and CGRP-induced IL-6 production. CT and CGRP have been shown to cross-react with each other. To exclude the possibility of this cross-reactivity, we studied the additive effects of CT and CGRP and the inhibitory effects of specific inhibitors. When 100 nM CT was added, cAMP accumulation stimulated by 10 nM CGRP (the maximal dose) was increased. CGRP (8-37), a specific CGRP receptor inhibitor, inhibited cAMP accumulation and IL-6 production induced by CGRP, but did not inhibit these effects when they were induced by CT. Salmon CT (8-32), a specific inhibitor of the CT receptor, inhibited cAMP accumulation induced by CT, but did not inhibit the effect induced by CGRP. These results demonstrated that CT can induce IL-6 production via cAMP accumulation and the effects of CT are mediated via its own receptors.

D-Amino Acids in the Nervous and Endocrine Systems

Amino acids are important components for peptides and proteins and act as signal transmitters. Only L-amino acids have been considered necessary in mammals, including humans. However, diverse D-amino acids, such as D-serine, D-aspartate, D-alanine, and D-cysteine, are found in mammals. Physiological roles of these D-amino acids not only in the nervous system but also in the endocrine system are being gradually revealed. N-Methyl-D-aspartate (NMDA) receptors are associated with learning and memory. D-Serine, D-aspartate, and D-alanine can all bind to NMDA receptors. H2S generated from D-cysteine reduces disulfide bonds in receptors and potentiates their activity. Aberrant receptor activity is related to diseases of the central nervous system (CNS), such as Alzheimers disease, amyotrophic lateral sclerosis, and schizophrenia. Furthermore, D-amino acids are detected in parts of the endocrine system, such as the pineal gland, hypothalamus, pituitary gland, pancreas, adrenal gland, and testis. D-Aspartate is being investigated for the regulation of hormone release from various endocrine organs. Here we focused on recent findings regarding the synthesis and physiological functions of D-amino acids in the nervous and endocrine systems.

Intra- and Intercellular Quality Control Mechanisms of Mitochondria

Mitochondria function to generate ATP and also play important roles in cellular homeostasis, signaling, apoptosis, autophagy, and metabolism. The loss of mitochondrial function results in cell death and various types of diseases. Therefore, quality control of mitochondria via intra- and intercellular pathways is crucial. Intracellular quality control consists of biogenesis, fusion and fission, and degradation of mitochondria in the cell, whereas intercellular quality control involves tunneling nanotubes and extracellular vesicles. In this review, we outline the current knowledge on the intra- and intercellular quality control mechanisms of mitochondria.

NG-nitro-l-[3h]arginine binding properties of neuronal nitric oxide synthase in rat brain

NG-Nitro-L-arginine (L-NNA), a derivative of L-arginine (L-Arg), is known as a pseudosubstrate and inhibitor for nitric oxide synthase (NOS). To clarify the regulatory mechanism of substrate-binding domain in neuronal NOS (nNOS), we examined the characteristics of NG-nitro-L-[3H]Arg (L-[3H]NNA) binding using the cytosolic fraction and purified nNOS from the rat cerebellum, in comparison with L-[14C]citrulline formation from L-[14C]Arg. The L-[3H]NNA binding was inhibited by L-NNA > NG-methyl-L-Arg > diphenyleneiodonium > L-Arg, but was not inhibited by L-citrulline and D-Arg. Thus, L-NNA seems to bind the substrate-binding domain in the nNOS with high affinity rather than L-Arg. Even in the absence of NADPH, tetrahydrobiopterin (BH4) and Ca2+, the L-[3H]NNA binding activity was observed in the cerebellar cytosol, although L-[14C]citrulline could not be produced from L-[14C]Arg. L-[3H]NNA binding was increased by BH4 alone and was markedly enhanced by NADPH plus BH4 (NADPH/BH4), but not by Ca2+/CaM. In contrast, L-[14C]citrulline was formed only in the presence of NADPH/BH4 and Ca2+. Similar results were obtained in purified nNOS. These results suggest that L-[3H]NNA seems to bind the substrate-binding domain in the nNOS but the binding affinity of L-Arg was lower than the affinity of L-NNA. Although the substrate binding is necessary to BH4 and NADPH, Ca2+/CaM are further necessary for the formation of NO and L-citrulline.

Commentary on the Phototoxicity and Absorption of Vitamin B2 and Its Degradation Product, Lumichrome

In this commentary, we present two views related to the study of riboflavin (vitamin B2): (i) future research into the photo toxicity of riboflavin and its photo-degradation product, lumichrome, should consider effects under visible light and ultraviolet (UV) light in skin because the photochemistry of these reactions differ; and (ii) future research should consider the possibility that excess lumichrome, which is metabolized from riboflavin by intestinal bacteria and is much less water-soluble than riboflavin, could be more readily absorbed and lead to symptoms that resemble those of fat-soluble vitamins.

Role and Cytotoxicity of Amylin and Protection of Pancreatic Islet β-Cells from Amylin Cytotoxicity

Amylin, (or islet amyloid polypeptide; IAPP), a 37-amino acid peptide hormone, is released in response to nutrients, including glucose, lipids or amino acids. Amylin is co-stored and co-secreted with insulin by pancreatic islet β-cells. Amylin inhibits food intake, delays gastric emptying, and decreases blood glucose levels, leading to the reduction of body weight. Therefore, amylin as well as insulin play important roles in controlling the level of blood glucose. However, human amylin aggregates and human amylin oligomers cause membrane disruption, endoplasmic reticulum (ER) stress and mitochondrial damage. Since cytotoxicity of human amylin oligomers to pancreatic islet β-cells can lead to diabetes, the protection of pancreatic islet β cells from cytotoxic amylin is crucial. Human amylin oligomers also inhibit autophagy, although autophagy can function to remove amylin aggregates and damaged organelles. Small molecules, including β-sheet breaker peptides, chemical chaperones, and foldamers, inhibit and disaggregate amyloid formed by human amylin, suggesting the possible use of these small molecules in the treatment of diabetes. In this review, we summarize recent findings regarding the role and cytotoxicity of amylin and the protection of pancreatic islet β-cells from cytotoxicity of amylin.

Induction of the expression of GABARAPL1 by hydrogen peroxide in C6 glioma cells

Ischemia-reperfusion or traumatic brain injury induces the accumulation of reactive oxygen species (ROS) in brain. ROS causes oxidative stress to astrocytes as well as neurons and oxidative stress induces the damage to organelles, proteins or lipids. The removal of damaged cellular cytosolic components is indispensable for the cell to keep the homeostasis. Macroautophagy (hereafter referred to as autophagy) is the process to degrade defective proteins and damaged organelles. In the process of autophagy, damaged cellular cytosolic components are isolated by autophagosomes. Microtubule-associated protein 1 light chain 3B (LC3B) plays a significant role in the autophagosome formation, and the conversion from unconjugated-LC3B (LC3B-I) to phosphatidylethanolamine (PE) conjugated-LC3B (LC3B-II) is the index of the activitation of autophagy. GABARAPL1 is the paralogue of LC3B and the function of GABARAPL1 is not fully understood. In this study, we demonstrated GABARAPL1 mRNA and protein expression are up-regulated by H2O2 in rat C6 glioma cells and the induction of GABARAPL1 by H2O2 was accompanied with the conversion from LC3B-I to LC3B-II, indicating the formation of autophagosomes. Thus, GABARAPL1 may play a role in autophagic process, which is induced by H2O2. However, elucidation of the function of GABARAPL1 in autophagy will require further studies.

The effects of herbal teas on drug permeability

Herbal teas such as those made from Houttuynia cordata have been consumed for generations for health promotion. Herbal teas contain many ingredients, and there is concern that herbal teas can affect the pharmacokinetics of drugs. In this study we examined the effect of herbal teas on drug permeability. We used the human colon carcinoma cell line Caco-2 as a model to study the permeability of two drugs across the intestinal cell membrane. We quantified of the amount of digoxin and verapamil passed from apical to basal membranes of Caco-2 cells with and without extracts (1 mg/mL or 10 mg/mL) of four different teas (Rubus suavissimus S. Lee, Ginkgo biloba, Houttuynia cordata, and Eucommia ulmoides). These extracts were made with hot water and dried. For our experiments, the dried extracts were resuspended in water. Our results showed that extracts from Rubus suavissimus S. Lee, Houttuynia cordata, and Eucommia ulmoides at a concentration of 1 mg/mL or 10 mg/mL did not affect digoxin permeability from apical to basal membranes of Caco-2 cells. However, an extract from Ginkgo biloba at a concentration of 10 mg/ mL significantly increased permeability of digoxin and verapamil. Though this concentration is higher than that of typical tea preparations, Ginkgo biloba extract may exert this effect by inhibiting drug export P-glycoprotein (P-gp) since both digoxin and verapamil are known to be transported by P-gp.