Juglone, a
quinone isolated from Juglans mandshurica Maxim, has previously been shown to be effective against
malignancy. The effect is at least partially due to stimulation of suicidal death or apoptosis of tumour cells. On the other hand,
juglone has been shown to counteract apoptosis, for example, of neurons. In analogy to apoptosis of nucleated cells, erythrocytes may enter eryptosis, a suicidal death characterized by cell shrinkage and breakdown of
phosphatidylserine asymmetry of the cell membrane with
phosphatidylserine exposure at the erythrocyte surface. Stimulators of eryptosis include increase in cytosolic Ca(2+) activity [(Ca(2+) )i]. This study explored whether
juglone stimulates eryptosis. To this end, erythrocyte volume was estimated from forward scatter,
phosphatidylserine exposure at the erythrocyte surface from
FITC annexin V binding,
ceramide abundance from binding of fluorescent
antibodies in flow cytometry and cytosolic
ATP with a
luciferin-
luciferase-based assay. As a result, a 24-hr exposure of human erythrocytes to
juglone (5 μM) significantly decreased erythrocyte forward scatter.
Juglone (1-5 μM) significantly increased the percentage of
annexin V binding cells.
Juglone (5 μM) significantly increased
ceramide abundance at the erythrocyte surface and decreased erythrocyte
ATP concentration. The effect of
juglone (10 μM) on
annexin V binding was slightly but significantly blunted by removal of extracellular Ca(2+) and by addition of
protein kinase C (PKC) inhibitor
staurosporine (1 μM). In conclusion,
juglone stimulates suicidal erythrocyte death or eryptosis at least in part by upregulation of
ceramide abundance, energy depletion and activation of PKC.