Hiromi Nakao

Increase in number of annexin V-positive living cells of rat thymocytes by intracellular Pb2+

Lead is ubiquitous in our environment and lead poisoning is a major public health problem worldwide. In this study, to see if intracellular Pb(2+) induces the exposure of phosphatidylserine in rat thymocyte membranes, we have examined the effect of PbCl(2) on rat thymocytes treated with A23187 using a flow cytometer with appropriate fluorescent indicators under nominally-Ca(2+)-free condition. PbCl(2) at 1-30 μM dose-dependently induced the exposure of phosphatidylserine on outer membranes, associated with increasing the concentration of intracellular Pb(2+). The potency of intracellular Pb(2+) to induce the apoptotic change in thymocyte membranes seems to be greater than those of intracellular Ca(2+) and Cd(2+). Results suggest that intracellular Pb(2+) triggers apoptosis of rat thymocytes. This action of Pb(2+) may be one of mechanisms for the lead-induced changes in immunity.

Cytotoxic Screening of Medicinal and Edible Plants in Okinawa, Japan, and Identification of the Main Toxic Constituent of Rhodea japonica (Omoto)

The cytotoxic activity of ethanol extracts from 53 parts of 36 species of medicinal and edible plants cultivated in Okinawa was measured by using K562 human leukemia cells by a flow cytometric method. Two extracts from Rhodea japonica and Hypericum chinense were cytotoxic at a concentration of 10 μg/ml. The main cytotoxic constituent of Rhodea japonica was isolated and identified to be rhodexin A, which has been isolated as a cardetonic agent of the plant. The IC50 value for rhodexin A against the growth of K562 cells was 19 nM, this activity being much stronger than that of ouabain (IC50, 60 nM).