Background/Aims: The natural anthraquinone derivative emodin (1,3,8-trihydroxy-6-methylanthraquinone) is a component of several Chinese medicinal herbal preparations utilized for more than 2000 years. The substance has been used against diverse disorders including malignancy, inflammation and microbial infection. The substance is effective in part by triggering suicidal death or apoptosis. Similar to apoptosis of nucleated cells erythrocytes may enter suicidal erythrocyte death or eryptosis, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Signaling involved in the triggering of eryptosis include increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), oxidative stress and ceramide. The present study aimed to test, whether emodin induces eryptosis and, if so, to elucidate underlying cellular mechanisms. Methods: Phosphatidylserine abundance at the cell surface was estimated from annexin-V-binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3-fluorescence, ROS formation from DCFDA dependent fluorescence, and ceramide abundance utilizing specific antibodies. Results: Exposure of human erythrocytes for 48 hours to emodin (≥ 10 µM) significantly increased the percentage of annexin-V-binding cells, and at higher concentrations (≥ 50 µM) significantly increased forward scatter. Emodin significantly increased Fluo3-fluorescence (≥ 10 µM), DCFDA fluorescence (75 µM) and ceramide abundance (75 µM). The effect of emodin on annexin-V-binding was significantly blunted but not abolished by removal of extracellular Ca²⁺. Conclusions: Emodin triggers phospholipid scrambling of the erythrocyte cell membrane, an effect at least in part due to stimulation of Ca²⁺ entry and paralleled by oxidative stress and ceramide appearance at the erythroctye surface.

Background/Aims: The bioactive steroid sapogenin diosgenin is considered for a wide variety of applications including treatment of malignancy. The substance counteracts tumor growth in part by stimulating apoptosis of tumor cells. Similar to apoptosis of nucleated cells, erythrocytes may enter suicidal death or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Signaling involved in the stimulation of eryptosis includes increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), oxidative stress and ceramide. The present study explored, whether diosgenin induces eryptosis and, if so, to decipher cellular mechanisms involved. Methods: Flow cytometry was employed to estimate phosphatidylserine exposure at the cell surface from annexin-V-binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3-fluorescence, ROS formation from DCF dependent fluorescence, and ceramide abundance utilizing specific antibodies. Hemolysis was quantified by determination of haemoglobin concentration in the supernatant. Results: A 48 hours exposure of human erythrocytes to diosgenin significantly increased the percentage of annexin-V-binding cells (≥ 5 µM), significantly decreased forward scatter (15 µM), significantly increased Fluo3-fluorescence (≥ 10 µM), significantly increased DCF fluorescence (15 µM), significantly increased ceramide abundance (15 µM) and significantly increased hemolysis (15 µM). The effect of diosgenin (15 µM) on annexin-V-binding was significantly blunted but not abolished by removal of extracellular Ca²⁺. Conclusions: Diosgenin stimulates eryptosis with erythrocyte shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect paralleled by and at least in part due to Ca²⁺ entry, oxidative stress and ceramide.

Background/Aims: The CDC25B inhibitor NSC-95397 triggers apoptosis of tumor cells and is thus considered for the treatment of malignancy. The substance is effective in part by modification of gene expression. Similar to apoptosis of nucleated cells erythrocytes may undergo eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Eryptosis may be triggered by increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), oxidative stress, ceramide, as well as activation of protein kinases. The present study explored, whether NSC-95397 induces eryptosis and, if so, to shed some light on the mechanisms involved. Methods: Phosphatidylserine exposure at the cell surface was estimated from annexin-V-binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3-fluorescence, ROS formation from DCFDA dependent fluorescence, and ceramide abundance utilizing specific antibodies. Results: A 48 hours exposure of human erythrocytes to NSC-95397 significantly increased the percentage of annexin-V-binding cells (≥ 1 µM), significantly decreased forward scatter (≥ 2.5 µM), and significantly increased Fluo3-fluorescence (≥ 1 µM), DCFDA fluorescence (5 µM) and ceramide abundance (≥ 5 µM). The effect of NSC-95397 (5 µM) on annexin-V-binding was slightly, but significantly blunted by removal of extracellular Ca²⁺ and by addition of the protein kinase C inhibitor staurosporine (1 µM). Conclusions: NSC-95397 triggers cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect in part requiring entry of Ca²⁺ and activation of staurosporine sensitive kinase(s).

Background/Aims: The analkaloid drug quinine is utilized mainly for the chemoprophylaxis of malaria. The multiple side effects of quinine include hemolytic anemia and hemolytic uremic syndrome, disorders involving suicidal erythrocyte death or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Signaling contributing to stimulation of eryptosis include increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), oxidative stress, ceramide and D4476 sensitive casein kinase. The present study explored the putative effect of quinine on eryptosis and elucidated cellular mechanisms involved. Methods: Phosphatidylserine exposure at the cell surface was estimated from annexin-V-binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3-fluorescence, ROS formation from DCF dependent fluorescence, and ceramide abundance utilizing specific antibodies. Results: A 48 hours exposure of human erythrocytes to quinine (≥ 50 µM) significantly increased the percentage of annexin-V-binding cells without significantly affecting forward scatter. Quinine significantly increased Fluo3-fluorescence, DCF fluorescence and ceramide abundance. The effect of quinine on annexin-V-binding was significantly blunted by removal of extracellular Ca²⁺ and by addition of D4476 (10 µM). Conclusions: Quinine triggers phospholipid scrambling of the erythrocyte cell membrane, an effect at least in part due to Ca²⁺ entry, oxidative stress, ceramide and D4476 sensitive casein kinase.

Background/Aims: The phytochemical polyphenol rottlerin is a potent activator of diverse Ca²⁺ -sensitive K⁺ channels. Those channels play a decisive role in the execution of eryptosis, the suicidal death of erythrocytes, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Signaling involved in the stimulation of eryptosis includes increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i) and ceramide. The present study explored, whether rottlerin induces eryptosis and, if so, to test for the involvement of Ca²⁺ entry and ceramide. Methods: Flow cytometry was employed to estimate phosphatidylserine exposure at the cell surface from annexin-V-binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3-fluorescence, and ceramide abundance utilizing specific antibodies. Hemolysis was quantified by determination of haemoglobin concentration in the supernatant. Results: A 48 hours exposure of human erythrocytes to rottlerin (1 - 5 µM) significantly increased the percentage of annexin-V-binding cells, an effect paralleled by significant decrease of forward scatter. Up to 5 µM rottlerin failed to significantly increase average Fluo3-fluorescence. Rottlerin (5 µM) did, however, significantly increase the ceramide abundance. Rottlerin (5 µM) further significantly increased hemolysis. The effect of rottlerin (5 µM) on annexin-V-binding was virtually abolished by removal of extracellular Ca²⁺. Conclusions: Rottlerin stimulates eryptosis with erythrocyte shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect paralleled by and at least in part due to Ca²⁺ entry and ceramide.

Background/Aims: The bis-indole alkaloid Fascaplysin is effective against malignancy, an effect at least partially due to stimulation of tumor cell apoptosis. Similar to apoptosis of nucleated cells, erythrocytes could enter suicidal erythrocyte death or eryptosis, characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), oxidative stress and ceramide. The present study explored, whether Fascaplysin induces eryptosis and, if so, to shed light on the cellular mechanisms involved. Methods: Flow cytometry was employed to estimate phosphatidylserine exposure at the cell surface from annexin-V-binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3-fluorescence, ROS formation from DCFDA dependent fluorescence, and ceramide abundance utilizing specific antibodies. Hemolysis was quantified from the hemoglobin concentration in the supernatant. Results: A 48 hours exposure of human erythrocytes to Fascaplysin (≥ 5 µM) significantly increased the percentage of annexin-V-binding cells, significantly decreased forward scatter, and significantly increased Fluo3-fluorescence, DCFDA fluorescence as well as ceramide abundance. The effect of Fascaplysin on annexin-V-binding and forward scatter was significantly blunted but not abolished by removal of extracellular Ca²⁺. Conclusions: Fascaplysin triggers cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect at least in part due to Ca²⁺ entry, oxidative stress and ceramide.

Background/Aims: The atypical retinoid E23-(40-hydroxyl-30-adamantylbiphenyl-4-yl) acrylic acid (ST1926, adarotene) is used in the treatment of malignancy. The effect of ST1926 is at least in part due to stimulation of apoptosis. Similar to apoptosis of nucleated cells, erythrocytes may enter eryptosis, the suicidal death of erythrocytes. Hallmarks of eryptosis include cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Signaling involved in the stimulation of eryptosis includes increase of cytosolic Ca²⁺ activity [Ca²⁺]_i, oxidative stress and ceramide. The present study explored, whether adarotene induces eryptosis and, if so, to test for the involvement of Ca²⁺ entry, oxidative stress and ceramide. Methods: Flow cytometry was employed to estimate phosphatidylserine exposure at the cell surface from annexin-V-binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo3-fluorescence, reactive oxygen species (ROS) formation from DCFDA dependent fluorescence, and ceramide abundance utilizing specific antibodies. Results: A 48 hours exposure of human erythrocytes to adarotene (9 µM) significantly increased the percentage of annexin-V-binding cells, an effect paralleled by significant decrease of forward scatter, as well as significant increase of Fluo3-fluorescence, DCFDA fluorescence, and ceramide abundance. The effect of adarotene (9 µM) on annexin-V-binding was significantly blunted but not abolished by removal of extracellular Ca²⁺. Conclusions: Adarotene stimulates phospholipid scrambling of the erythrocyte cell membrane, an effect paralleled by and at least in part due to Ca²⁺ entry, oxidative stress and ceramide.

Background/Aims: The thaliana phytoalexin Camalexin has been proposed for the treatment of malignancy. Camalexin counteracts tumor growth in part by stimulation of suicidal death or apoptosis of tumor cells. Similar to apoptosis of nucleated cells, erythrocytes may enter suicidal death or eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Cellular mechanisms contributing to the complex machinery executing eryptosis include increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), oxidative stress, ceramide, protein kinase C and caspases. The present study explored, whether Camalexin induces eryptosis and, if so, to shed light on mechanisms involved. Methods: Phosphatidylserine exposure at the cell surface was estimated from annexin-V-binding, cell volume from forward scatter, [Ca²⁺]_i from Fluo-3 fluorescence, ROS formation from DCFDA dependent fluorescence, and ceramide abundance utilizing specific antibodies. Results: A 48 hours exposure of human erythrocytes to Camalexin significantly increased the percentage of annexin-V-binding cells (≥ 10 µg/ml), significantly decreased forward scatter (≥ 5 µg/ml) and significantly increased Fluo-3-fluorescence (≥ 10 µg/ml), but did not significantly modify DCFDA fluorescence or ceramide abundance. The effect of Camalexin on annexin-V-binding was significantly blunted by removal of extracellular Ca²⁺, by kinase inhibitors staurosporine (1 µM) and chelerythrine (10 µM), as well as by caspase inhibitors zVAD (10 µM) and zIETD-fmk (50 µM). Conclusions: Camalexin triggers cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect at least in part depending on Ca²⁺ entry, as well as staurosporine and chelerythrine sensitive kinase(s) as well as zVAD and zIETD-fmk sensitive caspase(s).