Motoyuki Yajima

Cytoprotective effect of TRK-100, a prostacyclin analogue, against chemical injuries in cultured human vascular endothelial cells

We studied the cytoprotective effect of TRK-100, a chemically stable analogue of prostacyclin (PGI2), in the cultured human endothelial cells from umbilical vein. TRK-100 (10 and 100 nM) stimulated significantly proliferation of endothelial cells but did not affect PGI2 production in endothelial cells. Exposure of cultured endothelial cells to homocysteine (2.5 mM) or glucose (50 mM) caused concentration-dependent cytotoxicity, as evidenced by a decrease in number of viable cells. When endothelial cells were treated with TRK-100 simultaneously or prior to, but not after, exposure to injury substances, decreases in viable cell were significantly suppressed. The protective effect of TRK-100 against homocysteine-induced cytotoxicity also appeared in endothelial cells treated with acetylsalicylic acid, suggesting that endogenous PGI2 did not involve in the protective effect of TRK-100.

Dual mechanisms involved in development of diverse biological activities of islet-activating protein, pertussis toxin, as revealed by chemical modification of lysine residues in the toxin molecule

Islet-activating protein (IAP), pertussis toxin, is an oligomeric protein composed of an A-protomer and a B-oligomer. There seem to be at least two molecular mechanisms by which IAP exerts its various effects in vivo and in vitro. On the one hand, some of the effects were not significantly affected by acetamidination of the epsilon-amino groups of the lysine residues in the molecule. These include the activities in vitro (1) catalyzing ADP-ribosylation of one of the membrane proteins directly, (2) enhancing membrane adenylate cyclase activity in C6 cells, (3) reversing receptor-mediated inhibition of insulin or glycerol release from pancreatic islets or adipocytes, respectively, and the activities in vivo (4) inhibiting epinephrine-induced hyperglycemia, (5) potentiating glucose-induced hyperinsulinemia, (6) reducing hypertension and increasing the heart rate in genetically hypertensive rats. These activities are concluded to develop as a result of ADP-ribosylation catalyzed by the A-protomer which is rendered accessible to its intramembrane substrate thanks to the associated B-oligomer moiety. Thus, neither the enzymic activity of the A-protomer nor the transporting activity of the B-oligomer needs free amino groups of the lysine residues in the IAP molecule. On the other hand, additional effects of IAP, such as (1) mitogenic, (2) lymphocytosis-promoting, (3) histamine-sensitizing, (4) adjuvant and (5) vascular permeability increasing, were markedly suppressed by acetamidination of the intrapeptide lysine residues. The free epsilon-amino group of lysine would play an indispensable role in the firm (or divalent) attachment of the B-oligomer of IAP to the cell surface that is responsible for development of these activities.

Islet activating protein (IAP) derived from the culture supernatant fluid of Bordetella pertussis: Effect on spontaneous diabetic rats

SummaryThe early phase of insulin secretion to an oral glucose load was blunted in spontaneous diabetic rats. The blunted insulin secretion was associated with markedly impaired glucose tolerance. A single injection of the islet activating protein (IAP), a protein derived from the culture medium of Bordetella pertussis, into the spontaneous diabetic rats normalised glucose tolerance. The increase in insulin response to glucose was an important contributing factor to the improvement of glucose tolerance. This curative effect of the IAP on the diabetic state was of long duration; glucose tolerance remained virtually normal over a period of one month in the diabetic rats. Perfusion of the isolated pancreas of the diabetic rats pretreated with IAP showed an increase in insulin response to glucose and loss of suppression of glucagon secretion by noradrenaline.

Synthesis and biological evaluation of 2-amino-2-deoxy- and 6-amino-6-deoxy-cyclomaltoheptaose polysulfates as synergists for angiogenesis inhibition

2-Amino-2-deoxy-cyclomaltoheptaose was prepared from beta-cyclodextrin perbenzoate [heptakis(2,3,6-tri-O-benzoyl)cyclomaltoheptaose] by a series of reactions including selective de-O-benzoylation at C-2 of one of the perbenzoylated D-glucopyranosyl moieties, oxidation to the 2-ulose derivative, oxime formation, and reduction to the 2-amino-2-deoxy-D-glucose moiety. This compound and 6-amino-6-deoxycyclomaltoheptaose accessible from beta-cyclodextrin through the known procedure were sulfated to give polysulfated aminocyclomaltoheptaose derivatives (3, 5). Employing beta-cyclodextrin polysulfate as a reference compound, the synergistic effects of 3 and 5 for cortexolone or angiogenesis inhibitory activity were examined by rabbit-corneal micropocket assay system. In contrast to the significant anti-angiogenesis activity of the beta-cyclodextrin polysulfate-cortexolone pair, neither 3 nor 5 showed any cooperative activity with cortexolone in the inhibition of basic FGF-induced angiogenesis.

Hypoglycemia induced by α-adrenergic stimulation during alkalosis

Abstract Hypoglycemia developed during respiratory alkalosis in fasted rats. This hypoglycemia was markedly potentiated by the simultaneous injection of inhibitors of hepatic gluconeogenesis or a β-adrenergic blocking agent; was not influenced by anti-insulin serum; was attenuated by hexamethonium; and was abolished by an α-adrenergic blocking agent. The rate of removal of injected glucose by peripheral tissues increased during alkalosis in insulin-deficient rats. The uptake of [ 14 C]-glucose by th eadipose tissue in vivo, which is stimulated by a very minute amount of insulin, was also stimulated during alkalosis whether or not the circulating insulin was neutralized with anti-insulin serum. It was concluded that, in alkalotic rats, blood glucose is rapidly utilized by peripheral tissues dependent on α-adrenergic stimulation, but without mediation of insulin and that this leads to development of hypoglycemia.

An involvement of α-adrenergic stimulation in exercise-induced hypoglycemia

Abstract Hypoglycemia developed in fasted rats during forced swimming. This hypoglycemia was mostly abolished by phentolamine, an α-adrenolytic agent, or by hexamethonium; was potential by propanolol, a β-adrenolytic agent, of 5-methoxyindole-2-carboxylic acid, a gluconeogenic inhibitor; and was not affected by anti-insulin serum. The turnover rate of blood glucose estimated from the decay curve of blood [14C]glucose increased significantly during exercise. There was a slight but significantly increase during exercise in the transfer of 3-O-methyl-[14C]glucose into the muscle and adipose tissues, when it was corrected for by [3H]mannitol transfer to the same tissues. It is concluded that the α-receptor-mediated action of endogenous catecholamine stimulates peripheral glucose utilization leading to hydroglycemia during exercise. The action of α- and β-adrenergic mechanisms, directly on peripheral tissues or via insulin secretion, in fine regulation of blood glucose level is discussed.

Changes in Kinetic Properties of Cytosolic Phospholipase A2 in Activated Rat Neutrophils

The 85-kDa cytosolic phospholipase A2 (cPLA2) an arachidonic acid-preferential PLA2 isozyme, is distributed throughout a wide variety of animal tissues and cells. It preferentially hydrolyzes phospholipids containing arachidonic acid at the sn-2 position, translocates from the cytosol to the nuclear envelope in response to submicromolar concentrations of intracellular Ca2+, and is activated by phosphorylation1–3. On the basis of these features, cPLA2 is believed to regulate arachidonic acid release by mammalian cells following ligand-induced activation.