Biomedical subjects

Kyung-Min Lim

Publications and source records attributed to Kyung-Min Lim.

4 recordsLinked to original sources

PubMed2007

Lead-induced procoagulant activation of erythrocytes through phosphatidylserine exposure may lead to thrombotic diseases.

Lead (Pb) is a ubiquitous heavy metal pollutant in various environmental media, especially in food and drinking water. In human blood, about 95% of lead is associated with erythrocytes, suggesting that erythrocytes could be an important target of lead toxicity in the cardiovascular system. Recent studies suggested that erythrocytes could contribute to blood coagulation via phosphatidylserine (PS) exposure and resultant procoagulant activation. We investigated the effects of lead on the procoagulant activity of erythrocytes using in vitro human erythrocyte and in vivo rat models. In a flow cytometric analysis, lead (Pb2+) enhanced PS exposure on human erythrocytes in a concentration- and time-dependent manner. The concentration of lead (1-5 microM) used in the current investigation is well within the ranges observed in blood from lead-exposed populations. PS exposure by lead appeared to be mediated by increased intracellular calcium levels as shown by 19F-NMR and intracellular ATP depletion. Consistent with these findings, the activity of scramblase, which is important in the induction of PS exposure, was enhanced, whereas the activity of flippase, which translocates exposed PS to inner membrane, was inhibited by lead treatment. Furthermore, lead-exposed erythrocytes increased thrombin generation as determined by a prothrombinase assay and accelerated the coagulation process initiated by tissue factor in plasma. These procoagulant activations by lead were also confirmed in vivo. Administration of lead significantly enhanced PS exposure on erythrocytes and, more importantly, elevated thrombus formation in a rat venous thrombosis model. These results suggest that lead exposure can provoke procoagulant activity in erythrocytes by PS exposure, contributing to enhanced clot formation. These data will provide new insights into the mechanism of lead-induced cardiovascular diseases.

Adolescent↗

PubMed2006

Lysophosphatidic acid induces thrombogenic activity through phosphatidylserine exposure and procoagulant microvesicle generation in human erythrocytes.

OBJECTIVE: Although erythrocytes have been suggested to play a role in blood clotting, mediated through phosphatidylserine (PS) exposure and/or PS-bearing microvesicle generation, an endogenous substance that triggers the membrane alterations leading to a procoagulant activity in erythrocytes has not been reported. We now demonstrated that lysophosphatidic acid (LPA), an important lipid mediator in various pathophysiological processes, induces PS exposure and procoagulant microvesicle generation in erythrocytes, which represent a biological significance resulting in induction of thrombogenic activity. METHODS AND RESULTS: In human erythrocytes, LPA treatment resulted in PS exposure on remnant cells and PS-bearing microvesicle generation in a concentration-dependent manner. Consistent with the microvesicle generation, scanning electron microscopic study revealed that LPA treatment induced surface changes, alteration of normal discocytic shape into echinocytes followed by spherocytes. Surprisingly, chelation of intracellular calcium did not affect LPA-induced PS exposure and microvesicle generation. On the other hand, protein kinase C (PKC) inhibitors significantly reduced PS exposure and microvesicle generation induced by LPA, reflecting the role of calcium-independent PKC. Activation of PKC was confirmed by Western blot analysis showing translocation of calcium-independent isoform, PKCzeta, to erythrocyte membrane. The activity of flippase, which is important in the maintenance of membrane asymmetry, was also inhibited by LPA. Furthermore, LPA-exposed erythrocytes actually potentiated the thrombin generation as determined by prothrombinase assay and accelerated the coagulation process initiated by recombinant human tissue factor in plasma. The adherence of erythrocytes to endothelial cells, another important feature of thrombogenic process, was also stimulated by LPA treatment. CONCLUSIONS: These results suggested that LPA-exposed erythrocytes could make an important contribution to thrombosis mediated through PS exposure and procoagulant microvesicle generation.

Adolescent↗

PubMed2006

Shear stress-induced pH increase in plasma is mediated by a decrease in P(CO(2)): the increase in pH enhances shear stress-induced P-selectin expression in platelets.

To investigate shear stress-induced platelet activation, the cone-plate viscometer or the Couette rotational viscometer has been widely used. In a previous report, it was shown that shearing platelet-rich plasma using a Couette rotational viscometer could lead to an increase in pH by CO(2) release. However, any clear mechanism has not been provided. In this study, we examined whether shearing cell free plasma only using a cone-plate viscometer can also induce pH increase and studied the underlying mechanism of shear-induced pH increase by directly measuring total CO(2) (T(CO(2))) and CO(2) tension (P(CO(2))). When human plasma was sheared using a cone-plate viscometer, the pH of the human plasma increased time- and shear rate-dependently. Although T(CO(2)) of human plasma was not affected, P(CO(2)) was decreased by shearing, indicating that the decreased P(CO(2)) is associated with a pH increase of plasma. In addition, the pH of bicarbonate-containing suspension buffer was also shown to be increased by shearing; suggesting that the platelet studies using suspension buffers containing bicarbonate could be affected similarly. The effects of pH changes on shear stress-induced platelet activation were also investigated in the same in vitro systems. While shear stress-induced platelet aggregation was not affected by the pH changes, P-selectin expression was significantly increased in accordance with the pH increase. In conclusion, shear stress using a cone-plate viscometer induces pH increase in plasma or bicarbonate-containing suspension buffer through a P(CO(2)) decrease and the pH changes alone can contribute to platelet activation by enhancing shear stress-induced P-selectin expression.

Analysis of Variance↗

PubMed2005

Inorganic arsenite potentiates vasoconstriction through calcium sensitization in vascular smooth muscle.

Chronic exposure to arsenic is well known as the cause of cardiovascular diseases such as hypertension. To investigate the effect of arsenic on blood vessels, we examined whether arsenic affected the contraction of aortic rings in an isolated organ bath system. Treatment with arsenite, a trivalent inorganic species, increased vasoconstriction induced by phenylephrine or serotonin in a concentration-dependent manner. Among the arsenic species tested--arsenite, pentavalent inorganic species (arsenate), monomethylarsonic acid (MMAV), and dimethylarsinic acid (DMAV)--arsenite was the most potent. Similar effects were also observed in aortic rings without endothelium, suggesting that vascular smooth muscle plays a key role in enhancing vasoconstriction induced by arsenite. This hypercontraction by arsenite was well correlated with the extent of myosin light chain (MLC) phosphorylation stimulated by phenylephrine. Direct Ca2+ measurement using fura-2 dye in aortic strips revealed that arsenite enhanced vasoconstriction induced by high K+ without concomitant increase in intracellular Ca2+ elevation, suggesting that, rather than direct Ca2+ elevation, Ca2+ sensitization may be a major contributor to the enhanced vasoconstriction by arsenite. Consistent with these in vitro results, 2-hr pretreatment of 1.0 mg/kg intravenous arsenite augmented phenylephrine-induced blood pressure increase in conscious rats. All these results suggest that arsenite increases agonist-induced vasoconstriction mediated by MLC phosphorylation in smooth muscles and that calcium sensitization is one of the key mechanisms for the hypercontraction induced by arsenite in blood vessels.

Animals↗