Background:

Honokiol ((3,5-di-(2-propenyl)-1,1-biphenyl-2,2-diol), a component of Magnolia officinalis, stimulates apoptosis and is thus considered for the treatment of malignacy. In analogy to apoptosis of nucleated cells, erythrocytes may enter eryptosis, a suicidal death characterized by cell shrinkage and by cell membrane scrambling with phosphatidylserine-exposure at the erythrocyte surface. Eryptosis may be triggered following increase of cytosolic Ca²⁺-activity ([Ca²⁺]_i). The present study explored, whether honokiol elicits eryptosis.

Methods:

Cell volume has been estimated from forward scatter, phosphatidylserine-exposure from annexin V binding, hemolysis from hemoglobin release, [Ca²⁺]_i from Fluo3-fluorescence, and ceramide from fluorescent antibodies.

Results:

A 48 h exposure to honokiol was followed by a slight but significant increase of [Ca²⁺]_i (15 µM), significant decrease of forward scatter (5 µM), significant increase of annexin-V-binding (5 µM) and significant increase of ceramide formation (15 µM). Honikiol further induced slight, but significant hemolysis. Honokiol (15 µM) induced annexin-V-binding was significantly blunted but not abrogated in the nominal absence of extracellular Ca²⁺.

Conclusions:

Honokiol triggers suicidal erythrocyte death or eryptosis, an effect at least in part due to stimulation of Ca²⁺ entry and ceramide formation.