Taiho Shibata

Release of Excitatory Amino Acids from Cultured Hippocampal Astrocytes Induced by a Hypoxic‐Hypoglycemic Stimulation

Abstract: An excess release of excitatory amino acids (EAA) is an important factor for postischemic brain damage. In the present communication, we demonstrate that cultured hippocampal cells release EAA after hypoxic‐hypoglycemic treatment. The amounts of EAA released from astrocytes were appreciably above those released from neurons. Furthermore, the amount of aspartate released from astrocytes was comparable to that of glutamate, although the endogenous content of aspartate was one‐fifth that of glutamate. The endogenous content of aspartate in astrocytes increased even after hypoxic‐hypoglycemic treatment. These results suggests that ischemic neuronal death is due, at least in part, to the excitotoxicity of aspartate and glutamate‐derived from surrounding astrocytes.

Adenosine enhances intracellular Ca2+ mobilization in conjunction with metabotropic glutamate receptor activation by t-ACPD in cultured hippocampal astrocytes

2Cl-Adenosine, a non-metabolized adenosine agonist, enhanced the increase in intracellular Ca2+ concentration ([Ca2+]i) in cultured hippocampal astrocytes induced by (+-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (t-ACPD), a metabotropic glutamate agonist. In the absence of 2Cl-adenosine, the half effective concentration (EC50) of t-ACPD was about 80 microM. On the other hand, in the presence of 1 microM 2Cl-adenosine, the EC50 of t-ACPD shifted to about 5 microM, although the maximum [Ca2+]i did not change. The synergistic effect of 2Cl-adenosine with t-ACPD on [Ca2+]i elevation was not inhibited by the elimination of extracellular Ca2+, but was inhibited by A1-specific adenosine antagonists. These results indicate that adenosine can act via the A1 receptor as an endogenous co-activator of the metabolic processes induced by metabotropic glutamate receptor activation.

A possible mechanism for the hypoxia-hypoglycemia-induced release of excitatory amino acids from cultured hippocampal astrocytes

In order to elucidate the mechanism of release of excitatory amino acid (EAA) induced by hypoxiahypoglycemia (in vitro ischemia) from cultured hippocampal astrocytes, we compared the EAA release by in vitro ischemia with those by other treatments. The EAA release induced by in vitro ischemia treatment was rapid and reversible. The amount of released aspartate was comparable to that of glutamate, although the endogenous content of aspartate was one sixth that of glutamate. High-K (100 mM) treatment and the addition of 5 mM NaCN induced a rapid EAA release and the glutamate release was much greater than aspartate. Addition of 5 mM iodoacetate, a glycolysis inhibitor, induced a slow EAA release, and the amount of released aspartate was much higher than that of glutamate. On the other hand, the in vitro ischemia treatment and the addition of 5 mM NaCN induced only 20% reduction in ATP content for initial 5 min, whereas the addition of 5 mM iodiacetate induced a marked reduction. Our data suggest that ischemia-induced EAA release from astrocytes is a complex process in which local energy failure, inhibition of glycolysis, and depolarization of the cell membrane are involved.

IBUDILAST PROTECTS AGAINST NEURONAL DAMAGE INDUCED BY GLUTAMATE IN CULTURED HIPPOCAMPAL NEURONS

1. The effect of ibudilast, a drug that has been clinically used for asthma and the improvement of cerebrovascular disorders, was examined on glutamate neurotoxicity in cultured neurons from rat hippocampus.

Glycosylation of lipoprotein lipase in human subcutaneous and omental adipose tissues

Human adipose tissues from the abdomen (subcutaneous), thigh (subcutaneous) and omentum were incubated for 2 h with [35S]methionine. Then glycosylation of lipoprotein lipase (LPL) was analyzed by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of endoglycosidase H (endo H)-digested subunits of the 35S-labeled lipase. Adipose tissues from the abdomen, thigh, and omentum all synthesized LPL subunits with Mr = 57,000 composed of two types of subunits. One type was partially endo H-sensitive yielding a product with Mr = 55,000, indicating that it had one endo H-resistant and one endo H-sensitive oligosaccharide chain. The other type of subunit was totally endo H-sensitive yielding a product with Mr = 52,000. Subcutaneous adipose tissues contained nearly equal amounts of partially and totally endo H-sensitive subunits of LPL, whereas omental adipose tissues contained mainly partially endo H-sensitive subunits of LPL.

Metallosis caused by alumina ceramic screw fixation of grafted bone in a bipolar hip endoprosthesis

SummaryWe report a case of metallosis due to ceramic fragments in the inner bearing surface of the polyethylene cup of a bipolar hip prosthesis with fracture of the alumina ceramic screws used for grafted bone fixation. After bone-grafting acetabuloplasty with a Bateman bipolar endoprosthesis, gradual migration of the outer head occurred, and fracture of the screws was observed. Seven years after the operation, radiographs showed severe metallosis of the surrounding tissues. At revision, marked wear of the inner head was seen. Detailed examination revealed that many rough-edged ceramic particles originating from the fractured ceramic screws had become embedded in the inner surface of the polyethylene bearing insert. These extremely hard ceramic fragments had entered the prosthetic joint space during joint movement, thereafter causing continuous abrasion of the metal head. After revision, the concentration of the constituents of the prosthesis alloy in the serum decreased toward control levels. To prevent serious complications like those in the present case, screws should be inserted more than 1 cm from the outer head of a bipolar endoprosthesis, and the outer head should be removed as soon as possible if it comes into contact with the screws.

The Role of Bone Fracture at the Site of Carcinogen Exposure on Nickel Carcinogenesis in the Soft Tissue

The influence upon nickel subsulfide (α‐Ni3S2; Ni‐SS)‐induced carcinogenesis in the soft tissue of bone fracture at the site of Ni‐SS exposure was studied using female Fischer rats. During the one year of the experiment, the group subjected to bone fracture exhibited the shortest tumor induction time and survival time, and a significantly higher metastatic rate. The present study may suggest a model for the metastasis of human soft tissue tumors.