Biomedical subjects

Jin-Ho Chung

Publications and source records attributed to Jin-Ho Chung.

9 recordsLinked to original sources

PubMed2003

Arsenic-induced dysfunction in relaxation of blood vessels.

Several epidemiological studies have suggested that exposure to arsenic is strongly correlated with the development of cardiovascular diseases such as hypertension. To determine whether arsenic affects vasomotor tone in blood vessels, we investigated the effect of arsenic on vasorelaxation using isolated rat aortic rings in an organ-bath system. Treatment with arsenite inhibited acetylcholine-induced relaxation of the aortic rings in a concentration-dependent manner, whereas several other arsenic species did not have any effect. Consistent with these findings, the levels of guanosine 3',5'-cyclic monophosphate (cGMP) in the aortic rings were significantly reduced by arsenite treatment. In cultured human aortic endothelial cells, treatment with arsenite resulted in a concentration-dependent inhibition of endothelial nitric oxide synthase (eNOS). In addition, higher concentrations of arsenite decreased the relaxation induced by sodium nitroprusside (an NO donor) and 8-Br-cGMP (a cGMP analog) in aortic rings without endothelium. These in vitro results indicate that arsenite is capable of suppressing relaxation in blood vessels by inhibiting eNOS activity in endothelial cells and by impairing the relaxation machinery in smooth muscle cells. In vivo studies revealed that the reduction of blood pressure by acetylcholine infusion was significantly suppressed after arsenite was administered intravenously to rats. These data suggest that an impairment of vasomotor tone due to arsenite exposure may be a contributing factor in the development of cardiovascular disease.

Animals↗

PubMed2003

Antithrombotic activity of LB30057, a newly synthesized direct thrombin inhibitor.

An amidrazonophenylalanine derivative, LB30057, inhibits the catalytic activity of thrombin potently by interaction with the active site of thrombin, and has high water solubility. In the present study, we evaluated the effect of LB30057 on the biological activities of thrombin at various tissues, and determined whether thrombin inhibition by LB30057 could reduce the incidence of occlusive thrombosis in an in vivo animal model. Treatment with LB30057 to human plasma prolonged clotting times in a concentration-dependent manner. LB30057 suppressed significantly thrombin-induced phosphatidylserine (PS) exposure in platelets, suggesting that LB30057 could inhibit blood coagulation accelerated by PS exposure. In human platelets, soluble thrombin- and clot-induced platelet aggregation was inhibited by LB30057 potently. Consistent with this finding, LB30057 showed concentration-dependent inhibitory effects on serotonin secretion and P-selectin expression induced by thrombin in platelets. In the blood vessel isolated from the guinea pig, treatment with LB30057 resulted in a concentration-dependent inhibition of thrombin-induced vascular contraction. In vivo study revealed that LB30057 following oral administration significantly increased the time to occlusion and improved carotid arterial patency using rat carotid artery thrombosis model. All these results suggest that LB30057 is a potent inhibitor of biological activities of thrombin at various target tissues and, therefore, might be developed as an antithrombotic agent for treatment and prevention of thrombotic diseases.

Administration, Oral↗

PubMed2002

Temperature-dependent quinone cytotoxicity in platelets involves arylation.

Menadione (MEN), a representative quinone compound, produces cytotoxicity in many cells by arylation with protein thiols and oxidative stress due to redox cycling. Previously it was demonstrated that protein arylation appears to be a primary mechanism for MEN-induced toxicity in platelets. To test the hypothesis that temperature conditions may be important in MEN-induced cytotoxicity in noncancer cells, platelets were incubated with menadione at 25, 37, or 42 degrees C. As temperature was increased, MEN significantly enhanced lactate dehydrogenase (LDH) leakage. MEN-induced depletion of protein thiol levels also increased as temperature was elevated. To investigate the mechanism of temperature-dependent MEN cytotoxicity, MEN-induced platelet toxicity was compared to two other quinone substances. Benzoquinone (BQ), which acts via arylation, produced cytotoxic effects similar to those of MEN. Dimethoxy-1,4-naphthoquinone (DMNQ), which exerts toxicity via oxidative radical generation, failed to produce cytotoxicity at all three temperatures. While MEN and DMNQ enhanced O(2) consumption in a temperature-dependent manner, BQ did not affect this parameter. MEN, which possesses an electrophilic 3-position, was found to react with thiols to form a thioether linkage, a direct indicator of arylation. In the case of MEN uptake kinetics, the amount of cellular uptake was not different at various temperatures, but concentration of MEN in extracellular medium decreased temperature dependently. This might be due to increased arylation capacity binding to cellular proteins as temperature rises. These data suggest that MEN-induced platelet cytotoxicity involves arylation that is temperature related.

Animals↗

PubMed2002

Purification and characterization of a cytosolic, 42-kDa and Ca2+-dependent phospholipase A2 from bovine red blood cells: its involvement in Ca2+-dependent release of arachidonic acid from mammalian red blood cells.

It has become evident that a Ca(2+)-dependent release of arachidonic acid (AA) and subsequent formation of bioactive lipid mediators such as prostaglandins and leukotrienes in red blood cells (RBCs) can modify physiological functions of neighboring RBCs and platelets. Here we identified a novel type of cytosolic PLA(2) in bovine and human RBCs and purified it to apparent homogeneity with a 14,000-fold purification. The purified enzyme, termed rPLA(2), has a molecular mass of 42 kDa and reveals biochemical properties similar to group IV cPLA(2), but shows different profiles from cPLA(2) in several column chromatographies. Moreover, rPLA(2) did not react with any of anti-cPLA(2) and anti-sPLA(2) antibodies and was identified as an unknown protein in matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis. Divalent metal ions tested exhibited similar effects between rPLA(2) and cPLA(2), whereas mercurials inhibited cPLA(2) but had no effect on rPLA(2). Antibody against the 42-kDa protein not only precipitated the rPLA(2) activity, but also reacted with the 42-kDa protein from bovine and human RBCs in immunoblot analysis. The 42-kDa protein band was selectively detected in murine fetal liver cells known as a type of progenitor cells of RBCs. It was found that EA4, a derivative of quinone newly developed as an inhibitor for rPLA(2), inhibited a Ca(2+) ionophore-induced AA release from human and bovine RBCs, indicating that this enzyme is responsible for the Ca(2+)-dependent AA release from mammalian RBCs. Finally, erythroid progenitor cell assay utilizing diaminobenzidine staining of hemoglobinized fetal liver cells showed that rPLA(2) detectable in erythroid cells was down-regulated when differentiated to non-erythroid cells. Together, our results suggest that the 42-kDa rPLA(2) identified as a novel form of Ca(2+)-dependent PLA(2) may play an important role in hemostasis, thrombosis, and/or erythropoiesis through the Ca(2+)-dependent release of AA.

Animals↗

PubMed2002

Enhancement of platelet aggregation and thrombus formation by arsenic in drinking water: a contributing factor to cardiovascular disease.

Arsenic in drinking water is a worldwide health problem that is associated with cardiovascular disease, but the cause is currently unknown. Arsenic effects on platelets, which are important in development of cardiovascular disease, were examined in vitro and in a drinking water study using a rat animal model. Trivalent inorganic arsenic (arsenite) induced in vitro aggregation when platelets were exposed to subthreshold challenge by thrombin and several other agonists in a concentration-dependent manner, with arsenite being the most potent form tested. Arsenite also induced significant increases in serotonin secretion, thromboxane A(2) formation, and adhesion protein expression in platelets. Consistent with the in vitro studies, 4-week ingestion of arsenite-contaminated drinking water resulted in enhanced arterial thrombosis. Human platelets showed similar responses, suggesting that the effects seen in animal experiments are applicable to humans. These results will provide new insights into the mechanism of arsenic-induced cardiovascular disease. They will also allow regulatory agencies to estimate risk from arsenic-induced cardiovascular disease and to determine if drinking water regulatory levels based on human cancer studies will protect against noncancer effects associated with cardiovascular disease.

Animals↗

PubMed2002

The roles of ATP and calcium in morphological changes and cytotoxicity induced by 1,4-benzoquinone in platelets.

To understand the mechanism of 1,4-benzoquinone-induced cytotoxicity in platelets, the roles of ATP and calcium in platelet toxicity and morphological changes were investigated. Using scanning electron microscopy, morphological changes including membrane blebbing were observed in rat platelets 5 min after exposure to 1,4-benzoquinone, which were significantly different from shape changes (pseudopod formation) observed in response to physiological agonists. Benzoquinone-induced membrane blebbing of platelets was associated with rapid depletion of intracellular ATP and was independent of the presence of extracellular calcium. Benzoquinone-induced platelet lysis observed between 20 and 30 min was dependent on extracellular calcium and associated with increased cytosolic calcium. Cytotoxicity induced by 1,4-benzoquinone was inhibited by antagonists of calmodulin, suggesting that calmodulin could play an important role in platelet toxicity. These results suggested that the progression of events for benzoquinone-induced cytotoxicity in platelets was as follows: 1,4-benzoquinone depletes intracellular ATP; membrane blebbing occurs; calcium homeostasis is disrupted, activation of calmodulin-dependent processes results; finally cytotoxicity occurs.

Adenosine Triphosphate↗

PubMed2002

LB30057 inhibits platelet aggregation and vascular relaxation induced by thrombin.

Previous study showed that an amidrazonophenylalanine derivative, LB30057, which has high water solubility, inhibited the catalytic activity of thrombin potently by interaction with the active site of thrombin. In the current investigation, we examined whether LB30057 inhibited platelet aggregation and vascular relaxation induced by thrombin. Treatment with LB30057 to platelet-rich plasma (PRP) isolated from human blood resulted in a concentration-dependent inhibition of thrombin-induced aggregation. Values for IC50 and IC100 were 54 +/- 4 nM and 96 +/- 3 nM, respectively. This inhibition was agonist (thrombin) specific, since IC50 values for collagen and ADP were much greater than those for thrombin. In addition, concentration-dependent inhibitory effects were observed on the serotonin secretion induced by thrombin in PRP. Consistent with these findings, thrombin-induced increase in cytosolic calcium levels was inhibited in a concentration-dependent manner. When LB30057 was treated with aortic rings isolated from rats, LB30057 resulted in a concentration-dependent inhibition of thrombin-induced vascular relaxation. All these results suggest that LB30057 is a potent inhibitor of platelet aggregation and blood vessel relaxation induced by thrombin.

Animals↗

PubMed2002

Delayed ERK activation by ceramide reduces melanin synthesis in human melanocytes.

Sphingolipid metabolites regulate many aspects of cell growth and differentiation. However, the effects of sphingolipids on the growth and melanogenesis of human melanocytes are not known. In the present study, we investigated the effects of sphingolipid metabolites and the possible signalling pathways involved in human melanocytes. Our data show that C(2)-ceramide inhibits cell growth in a dose-dependent manner, whereas sphingosine-1-phosphate (SPP) has no effect. Moreover, we observed that the melanin content of the cells was significantly decreased by C(2)-ceramide. The pigmentation-inhibiting effect of C(2)-ceramide at 1-10 microM was stronger than that of kojic acid, tested at 1-100 microM. The tyrosinase activity of cell extracts was reduced by C(2)-ceramide treatment. However, in the cell-free system, C(2)-ceramide could not suppress tyrosinase, whereas kojic acid directly inhibited tyrosinase. These results suggest that C(2)-ceramide decreases the pigmentation of melanocytes indirectly regulating tyrosinase. Furthermore, we found that C(2)-ceramide decreased the protein expression of microphthalmia-associated transcription factor (MITF), which is required for tyrosinase expression. To identify the signalling pathway of ceramide, we studied the ability of C(2)-ceramide to influence extracellular signal-regulated protein kinase (ERK) and Akt/protein kinase B (PKB) activation. C(2)-ceramide induced a delayed activation of ERK ( > 1 h) and a much later activation of Akt/PKB ( > 3 h) in human melanocytes. In addition, the specific inhibition of the ERK and the Akt signalling pathways by PD98059 and LY294002, respectively, increased melanin synthesis. Thus, it seems that sustained ERK and Akt activation may lead to the suppression of cell growth and melanogenesis.

Adolescent↗

PubMed2002

Fibroblasts and ascorbate regulate epidermalization in reconstructed human epidermis.

Skin equivalent model provides a new investigating system to study the role of extracellular matrix and dermal factors such as collagen, basement membrane components and fibroblasts (Fb) which contribute to cell-cell and cell-matrix interactions. Although basement membrane factors is known to play an important role in epidermal differentiation and epidermal-matrix adhesion, comparative effects of these extracellular matrix and dermal factors on the reconstruction of epidermis are little known. In this study, we investigated effects of type I collagen (Coll I), type IV collagen plus laminin (LAM) coated Coll I (Coll IV+LAM), and human Fb enriched Coll I (Coll I+Fb) on epidermal reconstruction. When human keratinocytes were cultured on three different gels containing Coll I, Coll IV+LAM and Coll I+Fb, basal keratinocytes were cuboidal and perpendicular to the dermo-epidermal junction only in the gel containing Coll I+Fb. Proliferation marker expression was prominent and differentiation marker expression was similar with those of normal skin in the gel containing Coll I+Fb than in the other gel models. Since ascorbate is suspected to exert an effect as a modulator of proliferation and differentiation in keratinocytes, we tested the effects of ascorbate on human epidermis reconstruction. When 25 microg/ml ascorbate was added, disordered arrangement of epidermis was disappeared and differentiation marker expression was similar with its expression in normal skin. These data indicate that human Fb and a modulator of proliferation and differentiation such as ascorbate are essential for epidermalization in reconstructed epidermis.

Ascorbic Acid↗