Stimulation of Suicidal Erythrocyte Death by Tafenoquine

Abstract

Background/Aims: The 8-aminoquinoline tafenoquine has been shown to be effective against Plasmodia, Leishmania and Trypanosoma. The substance is at least in part effective by triggering apoptosis of the parasites. Similar to apoptosis, 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 regulation of eryptosis include increase of cytosolic Ca²⁺ activity ([Ca²⁺]_i), oxidative stress, ceramide, zVAD sensitive caspases, SB203580 sensitive p38 kinase, staurosporine sensitive protein kinase C as well as D4476 sensitive casein kinase. The present study explored, whether tafenoquine induces eryptosis and aimed to possibly identify 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 2′,7′-dichlorodihydrofluorescein diacetate (DCFDA) dependent fluorescence, and ceramide abundance utilizing specific antibodies. Results: A 48 hours exposure of human erythrocytes to tafenoquine (500 ng/ml) significantly increased the percentage of annexin-V-binding cells, significantly decreased forward scatter, significantly increased Fluo3-fluorescence, and significantly increased DCFDA fluorescence. Tafenoquine did not significantly modify ceramide abundance. The effect of tafenoquine on annexin-V-binding was significantly blunted but not abolished by removal of extracellular Ca²⁺. The effect of tafenoquine on annexin-V-binding was not significantly blunted by zVAD (10 µM), SB203580 (2 µM) or staurosporine (1 µM). The effect of tafenoquine on annexin-V-binding was significantly blunted but not abolished by D4476 (10 µM). Conclusions: Tafenoquine triggers cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect at least in part due to stimulation of Ca²⁺ entry, oxidative stress and possibly activation of casein kinase.

Effects of Antimalarial Tafenoquine on Blood Platelet Activity and Survival

“…Tafenoquine triggers, however, the suicidal death of erythrocytes, i.e. of cells lacking mitochondria [34]. Thus, mitochondria are not required for the effect of tafenoquine on cell death.…”

“…Tafenoquine could be further used for the treatment of trypanosoma brucei [28, 29] and leishmania [29-33] infection. Most recently, tafenoquine has been shown to trigger eryptosis, the suicidal death of erythrocytes characterized by cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane [34]. The effect was due to stimulation of Ca 2+ entry and oxidative stress [34].…”

Tafenoquine: A Step toward Malaria Elimination

“…Therefore, a non-enzymatic activation of 8-aminoquinolines may exist. Other than ROS production, tafenoquine also caused mitochondrial dysfunction accompanied by increased intracellular Ca 2+ levels in the related protozoan parasites Leishmania and Trypanosoma brucei . , Additionally, tafenoquine may trigger eryptosis (programmed cell death of erythrocytes) in Plasmodium -infected RBCs. , Whether these events are downstream of cellular stresses induced by tafenoquine or direct targets of this drug is currently unknown.…”

“…48,49 Additionally, tafenoquine may trigger eryptosis (programmed cell death of erythrocytes) in Plasmodiuminfected RBCs. 50,51 Whether these events are downstream of cellular stresses induced by tafenoquine or direct targets of this drug is currently unknown.…”

Tafenoquine: A Breakthrough Drug for Radical Cure and Elimination of Malaria

“…21 In addition to its antiplasmodial activities, TQ also causes red cell shrinkage and eryptosis or suicidal erythrocyte death, a process similar to apoptosis in nucleated cells. 22 The activity of TQ targeting the pre-erythrocytic (liver) stages of plasmodium species prevents the development of relapses in P. vivax malaria. A study from Thailand focusing on the transmission blocking potential of TQ, evaluated the efficacy of TQ against the sporogonic stage of the P. vivax parasite after letting mosquitoes feed on gametocytemic blood containing TQ.…”