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Background/Aims: The cyclin-dependent kinase 4 (CDK4) participates in the regulation of apoptosis of nucleated cells by altering transcriptional regulation of genes governing cell proliferation and cell death. Similar to apoptosis of nucleated cells, erythrocytes may enter eryptosis, which is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) exposure at the cell surface. As mature erythrocytes lack nuclei, acute stimulation of eryptosis cannot result from altered gene expression. Eryptosis is triggered by isotonic cell shrinkage following Cl- removal (replacement with the impermeant organic anion gluconate) or by oxidative stress (exposure to 0.3 mM tertbutyl-hydroperoxide [tBOOH]). The present study explored whether CDK4 is expressed in erythrocytes and whether the CDK4 inhibitors II (NSC625987) and III (ryuvidine) influence eryptosis. Methods: Western blotting was utilized for determination of the presence of CDK4 protein in human erythrocytes, and FACS analysis to determine Fluo3 fluorescence (reflecting cytosolic Ca2+), annexin-V-binding (reflecting PS-exposure) and forward scatter (reflecting cell volume). Results: CDK4 protein was present in human erythrocytes. Cl- removal was followed by decrease of forward scatter and increase of both annexin-V-binding and Fluo3 fluorescence, an effect significantly curtailed by CDK4 inhibitors II and III. Furthermore, CDK4 inhibition blunted enhanced PS-exposure elicited by tBOOH treatment. Conclusions: The present observations disclose the presence of CDK4 protein in human erythrocytes and the suppression of suicidal erythrocyte death by pharmacological inhibition of CDK4.

Background/Aims: Epidemiological evidence suggests that vitamin D deficiency is associated with anemia. The potent metabolite 1,25(OH)2 vitamin D3 [1,25(OH)2D3] activates various signaling cascades regulating a myriad of cellular functions including suicidal cell death or apoptosis. Suicidal death of erythrocytes or eryptosis is characterized by cell shrinkage and cell membrane scrambling leading to phosphatidylserine (PS) externalization. Stimulation of eryptosis may limit lifespan of circulating erythrocytes and thus cause anemia. In the present study, we explored the effect of a high vitamin D diet (10,000 I.U. vitamin D for 14 days) in mice on eryptosis. Methods: Plasma concentrations of erythropoietin were estimated using an immunoassay kit, blood count using an electronic hematology particle counter, relative reticulocyte numbers using Retic-COUNT® reagent, PS exposure at the cell surface from annexin V binding, cell volume from forward scatter, and cytosolic Ca2+ ([Ca2+]i) from Fluo3-fluorescence in FACS analysis. Results: Vitamin D treatment decreased mean corpuscular volume, reticulocyte count, and plasma erythropoietin levels. Vitamin D treatment slightly but significantly decreased forward scatter but did not significantly modify spontaneous PS exposure and [Ca2+]i of freshly drawn erythrocytes. Vitamin D treatment augmented the stimulation of PS exposure and cell shrinkage following exposure to hyperosmotic shock (addition of 550 mM sucrose) or energy depletion (glucose removal) without significantly modifying [Ca2+]i. Conclusions: The present observations point to a subtle effect of exogenous vitamin D supplementation on erythrocyte survival.

Background/Aims: Anemia, a common condition in the elderly, could result from impaired formation and/or from accelerated loss of circulating erythrocytes. The latter could result from premature suicidal erythrocyte death or eryptosis characterized by phosphatidylserine (PS) exposure at the erythrocyte surface. Triggers of eryptosis include increased cytosolic Ca2+-concentration ([Ca2+]i), oxidative stress and ceramide. The present study explored whether eryptosis is altered in elderly individuals and, if so, to identify underlying mechanisms. Methods: Blood was drawn from healthy young (n=11, age 31.3±1.7 years) and elderly (n=16, age 88.6±0.9 years) individuals. PS exposure was estimated from annexin V-binding, cell volume from forward scatter, [Ca2+]i from Fluo3-fluorescence, reactive oxygen species (ROS) from 2',7'dichlorodihydrofluorescein fluorescence, reduced glutathione (GSH) from mercury orange fluorescence and ceramide from FITC-conjugated antibody binding in flow cytometry. Measurements were made in erythrocytes from freshly drawn blood and in erythrocytes exposed in vitro for 24 h to plasma from young or elderly individuals. Results: Elderly individuals suffered from severe anemia (hemoglobin 10.5±0.3 g/100 ml) despite enhanced number of reticulocytes (2.3±0.2%). The percentage of PS-exposing erythrocytes was significantly higher in the elderly (2.5±0.2%) than in the young volunteers (1.3±0.1%). The increase in PS exposure was paralleled by significant increase of ROS and significantly decreased levels of reduced GSH. Erythrocyte [Ca2+]i, and ceramide abundance tended to be higher in the elderly, differences, however, not reaching statistical significance. Conclusions: The anemia of elderly individuals is mainly if not exclusively due to enhanced eryptosis, resulting at least in part from GSH deficiency and increased oxidative stress.

Background/Aims: Cryptotanshinone, a component of Salvia miltiorrhiza Bunge roots, may trigger suicidal death or apoptosis of tumor cells and has thus been recommended for the prevention and treatment of malignancy. On the other hand, Cryptotanshinone has been shown to counteract apoptosis of neurons and hepatocytes. Similar to apoptosis of nucleated cells, erythrocytes may enter eryptosis, a suicidal death characterized by cell shrinkage and phosphatidylserine translocation to the erythrocyte surface. Eryptosis may be triggered by increase of cytosolic Ca2+-activity ([Ca2+]i). The present study explored whether Cryptotanshinone stimulates eryptosis. Methods: Forward scatter was taken as measure of cell volume, annexin V binding for identification of phosphatidylserine-exposing erythrocytes and Fluo3-fluorescence for determination of [Ca2+]i. Results: A 48 h exposure of human erythrocytes to Cryptotanshinone (10 µM) was followed by significant decrease of forward scatter, significant increase of the percentage annexin-V-binding cells and significant increase of [Ca2+]i. The effect of Cryptotanshinone (1 µM) on annexin-V-binding was virtually abrogated by removal of extracellular Ca2+. Conclusion: Cryptotanshinone is a powerful stimulator of suicidal erythrocyte death or eryptosis, which is effective mainly, if not exclusively, by stimulation of Ca2+ entry.

Background/Aims: Gedunin, an inhibitor of heat shock protein HSP90, triggers apoptosis of tumor cells and is thus effective against malignancy. Moreover, the drug has antimalarial potency. In analogy to apoptosis of nucleated cells, erythrocytes may enter suicidal death or eryptosis, which is characterized by cell shrinkage and by phosphatidylserine translocation to the erythrocyte surface. Eryptosis may be triggered by increase of cytosolic Ca2+-activity ([Ca2+]i). The present study explored whether gedunin stimulates eryptosis. Methods: Forward scatter was determined to estimate cell volume, annexin V binding to identify phosphatidylserine-exposing erythrocytes, hemoglobin release to depict hemolysis, and Fluo3-fluorescence to quantify [Ca2+]i. Results: A 48 h exposure of human erythrocytes to gedunin significantly increased [Ca2+]i (12 µM), significantly decreased forward scatter (24 µM) and significantly increased annexin-V-binding (12 µM). The effect of gedunin (24 µM) on annexin-V-binding was virtually abrogated by removal of extracellular Ca2+. Conclusion: Gedunin stimulates suicidal erythrocyte death or eryptosis, an effect mainly if not exclusively due to stimulation of Ca2+ entry.

Shikonin, the most important component of Lithospermum erythrorhizon, has previously been shown to exert antioxidant, anti-inflammatory, antithrombotic, antiviral, antimicrobial and anticancer effects. The anticancer effect has been attributed to the stimulation of suicidal cell death or apoptosis. Similar to the apoptosis of nucleated cells, erythrocytes may experience eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and by phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include the increase of cytosolic Ca2+-activity ([Ca2+]i) and ceramide formation. The present study explored whether Shikonin stimulates eryptosis. To this end, Fluo 3 fluorescence was measured to quantify [Ca2+]i, forward scatter to estimate cell volume, annexin V binding to identify phosphatidylserine-exposing erythrocytes, hemoglobin release to determine hemolysis and antibodies to quantify ceramide abundance. As a result, a 48 h exposure of human erythrocytes to Shikonin (1 µM) significantly increased [Ca2+]i, increased ceramide abundance, decreased forward scatter and increased annexin V binding. The effect of Shikonin (1 µM) on annexin V binding was significantly blunted, but not abolished by the removal of extracellular Ca2+. In conclusion, Shikonin stimulates suicidal erythrocyte death or eryptosis, an effect at least partially due to the stimulation of Ca2+ entry and ceramide formation.

Background: Novobiocin, an aminocoumarin antibiotic, interferes with heat shock protein 90 and hypoxia inducible factor dependent gene expression and thus compromises cell survival. Similar to survival of nucleated cells, erythrocyte survival could be disrupted by eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and by phospholipd scrambling of the cell membrane with phosphatidylserine translocation to the erythrocyte surface. Triggers of eryptosis include increase of cytosolic Ca2+-activity ([Ca2+]i). The Ca2+ sensitivity of phospholipid scrambling is enhanced by ceramide. The present study explored, whether novobiocin elicits eryptosis. Methods: [Ca2+]i was estimated from Fluo3-fluorescence, ceramide abundance utilizing fluorescent antibodies, cell volume from forward scatter, phosphatidylserine-exposure from annexin V binding. Results: A 48 hours exposure to novobiocin (500 µM) was followed by a significant increase of [Ca2+]i, decrease of forward scatter, increase of annexin-V-binding and enhanced ceramide formation. Removal of extracellular Ca2+ virtually abrogated the increase of annexin-V-binding following novobiocin exposure. Conclusions: Novobiocin stimulates eryptosis, an effect at least in part due to entry of extracellular Ca2+ and formation of ceramide.

The selective cyclooxygenase-2 (COX-2) inhibitor celecoxib triggers apoptosis of tumor cells and is thus effective against malignancy. The substance is at least partially effective through mitochondrial depolarization. Even though lacking mitochondria, erythrocytes may enter apoptosis-like suicidal death or eryptosis, which is characterized by cell shrinkage and by phosphatidylserine translocation to the erythrocyte surface. Eryptosis may be triggered by increase of cytosolic Ca2+-activity ([Ca2+]i). The present study explored whether celecoxib stimulates eryptosis. Forward scatter was determined to estimate cell volume, annexin V binding to identify phosphatidylserine-exposing erythrocytes, hemoglobin release to depict hemolysis, and Fluo3-fluorescence to quantify [Ca2+]i. A 48 h exposure of human erythrocytes to celecoxib was followed by significant increase of [Ca2+]i (15 µM), significant decrease of forward scatter (15 µM) and significant increase of annexin-V-binding (10 µM). Celecoxib (15 µM) induced annexin-V-binding was blunted but not abrogated by removal of extracellular Ca2+. In conclusion, celecoxib stimulates suicidal erythrocyte death or eryptosis, an effect partially due to stimulation of Ca2+ entry.

Background: Patulin, the most common mycotoxin in apples and apple-derived products, triggers apoptosis and has thus been considered for the treatment of cancer. Similar to apoptosis of nucleated cells, erythrocytes may enter suicidal death or eryptosis, which is characterized by cell shrinkage and by cell membrane scrambling leading to phosphatidylserine-exposure at the erythrocyte surface. Stimulators of eryptosis include increase of cytosolic Ca2+-activity ([Ca2+]i). The present study explored, whether exposure of human erythrocytes to patulin is followed by eryptosis. Methods: Forward scatter was measured to estimate cell volume, annexin V binding to detect phosphatidylserine-exposure, hemoglobin release to quantify hemolysis, and Fluo3-fuorescence to determine [Ca2+]i. Results: A 48 h exposure to patulin significantly increased [Ca2+]I (5 µM), significantly decreased forward scatter (5 µM) and significantly increased annexin-V-binding (2.5 µM). Patulin (10 µM) induced annexin-V-binding was virtually abrogated by removal of extracellular Ca2+. Conclusion: Patulin stimulates Ca2+ entry into erythrocytes, an effect triggering suicidal erythrocyte death or eryptosis.

Coexpression of the serum and glucocorticoid inducible kinase 1 (SGK1) up-regulates Kv channel activity in Xenopus oocytes and human embryonic kidney cells. To investigate the physiological impact of SGK1 dependent Kv channel regulation, we recorded whole-cell currents in lung fibroblasts from SGK1 knockout mice (sgk1-/-) and wild-type littermates (sgk1+/+). Serum-grown mouse lung fibroblasts (MLF) from both genotypes exhibited voltage-gated outwardly rectifying K+-currents with time-dependent activation (tact~3 msec), slow inactivation (tinact~700 msec), use-dependent inactivation, and (partial) inhibition by K+ channel blockers TEA, 4-AP, and margatoxin. In serum grown MLF peak Kv current density at +100 mV was significantly lower in sgk1-/- (14??2 pA/pF, n?=?13) than in sgk1+/+ (31??4 pA/pF, n?=?16). PCR amplification of different Kv1 and Kv3 subunits from mouse fibroblasts demonstrated the expression of Kv1.1-1.7, Kv3.1, and Kv3.3 mRNA in both sgk1+/+ and sgk1-/- cells. Upon serum deprivation Kv currents almost disappeared in sgk1+/+ (4??1 pA/pF, n?=?11) but not in sgk1-/- (10??1 pA/pF, n?=?6) MLF. Accordingly, following serum deprivation Kv current density was significantly lower in sgk1+/+ than in sgk1-/-. Stimulation of serum-depleted cells with dexamethasone (dex) (1 M, 1 day), IGF-1 (6.7 M, 46 h) or both, significantly activated Kv currents in sgk1+/+ but not in sgk1-/- MLF. In the presence of both, dex and IGF-1, the Kv current density was significantly larger in sgk1+/+ (27??3 pA/pF, n?=?12) than in sgk1-/- (13??3 pA/pF, n?=?10) cells. Similar to MLF, Kv currents were significantly higher in sgk1+/+ mouse tail fibroblasts (MTF). In sgk1+/+ but not sgk1-/- MTF the Kv currents were inhibited upon serum deprivation and reincreased after stimulation of serum deprived MTF with dex (1 M, 1 day) and afterwards with IGF-1 (6.7 M, 46 h). According to Fura-2-fluorescence capacitative Ca2+ entry was lower in sgk1-/- MTF compared to sgk1+/+ MTF. Upon serum deprivation capacitative Ca2+ entry decreased significantly in sgk1+/+ but not in sgk1-/- MTF. Stimulation of depleted cells with dex (1 M, 1 day) and afterwards with IGF-1 (6.7 M, 46 h) reincreased capacitative Ca2+ entry in sgk1+/+ MTF, whereas in sgk1-/- cells it remained unchanged. In conclusion, lack of SGK1 does not abrogate Kv channel activity but abolishes regulation of those channels by serum, glucocorticoids and IGF-1, an effect influencing capacitative Ca2+ entry. 2004 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]