Biomedical subjects

K Kitatani

Publications and source records attributed to K Kitatani.

7 recordsLinked to original sources

PubMed2000

Acceleration by ceramide of calcium-dependent translocation of phospholipase A2 from cytosol to membranes in platelets.

The effect of ceramide on Ca2+-dependent translocation of cytosolic phospholipase A2 (cPLA2) to membranes was studied. Pretreatment of platelets with sphingomyelinase or C6-ceramide (N-hexanoylsphingosine) led to apparent enhancement of Ca2+-ionophore A23187-stimulated arachidonic acid release but did not affect the cytosolic phospholipase A2 (cPLA2) activity. Under these conditions, the cPLA2 proteins in membranes increased significantly, compared with those by A23187 alone. Sphingomyelinase and C6-ceramide, but not C6-dihydroceramide, a control analog of C6-ceramide, also facilitated the Ca2+-dependent increase in the cPLA2 protein, as well as the activity, in membranes induced by addition of Ca2+ into platelet lysate. Protein kinase Calpha, which possesses a Ca2+-dependent lipid binding domain, was increased in membranes in a Ca2+-dependent manner, but the increase was not accelerated by sphingomyelinase or C6-ceramide. These findings suggest that ceramide in membranes potentiates Ca2+-dependent cPLA2 translocation from cytosol to membranes, probably through modification of membrane phospholipid organization.

Animals↗

PubMed2000

Characterization of recombinant human adipocyte-derived leucine aminopeptidase expressed in Chinese hamster ovary cells.

Adipocyte-derived leucine aminopeptidase (A-LAP) is a recently identified novel member of the M1 family of zinc-metallopeptidases. Transfection of the A-LAP cDNA into COS-7 cells resulted in the secretion of the enzyme. In this study, recombinant A-LAP was expressed in Chinese hamster ovary cells, purified to homogeneity and its enzymatic properties were characterized. The purified enzyme was active towards a synthetic substrate, L-leucyl-p-nitroanilide, yielding a V(max) of 3.55 micromol/min/mg and a K(m) of 1.28 mM, and was shown to be a monomeric protein with molecular mass of 120 kDa in solution. By monitoring the sequential N-terminal amino acid liberation, it was found that the enzyme hydrolyzes a variety of bioactive peptides, including angiotensin II and kallidin. Immunohistochemical analysis indicated that the enzyme is expressed in the cortex of the human kidney, where tissue kallikrein is localized. Taken together, these results indicate that A-LAP possesses a broad substrate specificity towards naturally occurring peptide hormones and suggest that it plays a role in the regulation of blood pressure through the inactivation of angiotensin II and/or the generation of bradykinin in the kidney.

Adipocytes↗

PubMed2000

Involvement of lipoxygenase pathway in docosapentaenoic acid-induced inhibition of platelet aggregation.

The effects of docosapentaenoic acid (DPA) on platelet aggregation and arachidonic acid metabolism were studied in comparison to those of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Collagen- or arachidonic acid-stimulated platelet aggregation was inhibited dose-dependently by n-3 fatty acids, among which DPA was the most potent inhibitor. These fatty acids inhibited U46619-induced aggregation but to almost the same extent. No effect of the acids on thrombin-induced aggregation was observed. Furthermore, these fatty acids suppressed thromboxane A2 formation by platelets which were exposed to collagen or thrombin, or by platelets to which arachidonic acid was added. In these experiments also, DPA was the most potent inhibitor, whereas DHA was the most effective inhibitor of cyclooxygenase-1 activity. DPA enhanced formation of 12-hydroxyeicosatetraenoic acid in response to collagen or from arachidonic acid by intact platelets, while the other two acids had less of an effect. These results suggest that DPA possesses potent activity for interfering with the cyclooxygenase pathway and accelerating the lipoxygenase pathway, thus inhibiting platelet aggregation most effectively.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗

PubMed2000

Role of phospholipase D-derived phosphatidic acid as a substrate for phospholipase A2 in RBL-2H3 cells.

The implications of phospholipase D (PLD) in cytosolic phospholipase A2 (cPLA2) activation were studied in a mast cell line, RBL-2H3, upon stimulation with antigen. Antigen-stimulated prostaglandin D2 generation was apparently suppressed by ethanol with a concomitant decrease in phosphatidic acid (PA) formation. The prostaglandin D2 generation was also inhibited almost completely by methyl arachidonyl fluorophosphonate (MAFP), an inhibitor of cPLA2, but not by diacylglycerol lipase inhibitor. Furthermore, stimulation with antigen resulted in an increase in lysophosphatidic acid formation, which was suppressed by MAFP in parallel with an increase in PA formation. These results suggest that PA formed by the catalytic action of PLD is used as a substrate for cPLA2, thus PLD regulates cPLA2 activation in antigen-stimulated RBL-2H3 cells.

Animals↗

PubMed1999

Stimulation by ceramide of phospholipase A2 activation through a mechanism related to the phospholipase C-initiated signaling pathway in rabbit platelets.

To study the involvement of sphingolipids in glycerophospholipid metabolism, the contribution of ceramide to the activation of group IV cytosolic phospholipase A2 (cPLA2) was investigated in platelets using cell-permeable C6-ceramide (N-hexanoylsphingosine). The addition of ceramide led to potentiation of thrombin-induced activation of cPLA2 and mitogen-activated protein kinase (MAPK) as well as arachidonic acid release and lysophosphatidylcholine formation. However, ceramide by itself did not induce any response. The arachidonic acid release due to the synergistic action of ceramide and thrombin was inhibited by PD98059, a MAPK kinase inhibitor. Ceramide also stimulated thrombin-induced protein kinase C (PKC) activation, but ceramide by itself failed to do so. Furthermore, ceramide synergistically enhanced diacylglycerol (DAG) formation and Ca2+ mobilization with thrombin, and also DAG formation with Ca2+-ionophore A23187. The DAG formation in response to ceramide with thrombin or A23187, as well as arachidonic acid release with thrombin were completely inhibited by U73122, a phospholipase C (PLC) inhibitor. These results suggest that ceramide triggers PLC activation through its synergistic action with thrombin, and subsequently potentiates the sequential PKC-MAPK cascade-cPLA2 pathway, thus resulting in enhancement of arachidonic acid release.

Animals↗

PubMed1999

Ceramide enhances susceptibility of membrane phospholipids to phospholipase A2 through modification of lipid organization in platelet membranes.

The effects of ceramide on agonist-stimulated phospholipase A2 (PLA2) activity were studied in platelets. Cell-permeable C6-ceramide (N-hexanoylsphingosine) exogenously added to platelet suspension enhanced U46619-stimulated arachidonic acid release and lysophosphatidylcholine production. Treatment of platelets with sphingomyelinase also led to an enhancement of the release. The enhanced arachidonic acid release by exogenous ceramide was completely inhibited by methyl arachidonyl fluorophosphonate, a cytosolic PLA2 inhibitor. However, U46619-stimulated PLA2 activity was not significantly potentiated by ceramide. These results suggest that enrichment of ceramide in membranes causes modification of intermolecular organization, leading to increased susceptibility of substrate phospholipids to PLA2.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1998

[Ipriflavone].

Ipriflavone (7-isopropoxyisoflavone), a non-hormonal isoflavone derivative, is currently used in several countries for prevention and treatment of postmenopausal osteoporosis. This compound is devoid of estrogenic activity in humans, but increases the activity of estrogens. Ipriflavone has been shown to be effective in reducing bone turnover rate mainly through an inhibition of bone resorption, and has been effect to stimulate of bone formation. Inhibitory effect of ipriflavone on bone resorption has been demonstrated both directly by the activation of mature osteoclast and the formation of new osteoclasts by stimulating estrogen-induced calcitonin secretion by thyroids in vivo. There are some evidence that ipriflavone has direct effect on bone formation. Several clinical studies have demonstrated that bone mineral density (BMD) was increased or maintained in patients treated with ipriflavone. Recently, a large multicentral study, Ipriflavone Multicenter European Fracture Study (IMEFS), was designed in order to investigate the efficacy of ipriflavone on the prevention of vertebral and the effect on BMD in women with postmenopausal osteoporosis.

Bone Remodeling↗