Calcium ions, drug action and the red cell membrane

In vitro delayed response to dihydroartemisinin of malaria parasites infecting sickle cell erythocytes

BACKGROUND

Decreased efficacy of artemisinin-based combination therapy (ACT) for Plasmodium falciparum malaria has been previously reported in patients with sickle cell disease (SCD). The main purpose of this study was to investigate the in vitro susceptibility of isolates to dihydro-artemisinin (DHA) to provide a hypothesis to explain this treatment failure.

METHODS

Isolates were collected from patients attending health centres in Abidjan with uncomplicated P. falciparum malaria. The haemoglobin type has been identified and in vitro drug sensitivity tests were conducted with the ring stage assay and maturation inhibition assay.

RESULTS

134 isolates were obtained. Parasitaemia and haemoglobin levels at inclusion were lower in patients with haemoglobin HbSS and HbSC than in patients with normal HbAA. After ex vivo RSA and drug inhibition assays, the lowest rate of parasitic growth was found with isolates from HbAS red cells. Conversely, a significantly higher survival rate of parasites ranging from 15 to 34% were observed in isolates from HbSS. Isolates with in vitro reduced DHA sensitivity correlate with lower RBC count and haematocrit and higher parasitaemia at inclusion compared to those with isolates with normal DHA sensitivity. However, this decrease of in vitro sensitivity to DHA was not associated with Kelch 13-Propeller gene polymorphism.

CONCLUSION

This study highlights an in vitro decreased sensitivity to DHA, for isolates collected from HbSS patients, not related to the Pfkelch13 gene mutations. These results are in line with recent studies pointing out the role of the redox context in the efficacy of the drug. Indeed, SCD red cells harbour a highly different ionic and redox context in comparison with normal red cells. This study offers new insights into the understanding of artemisinin selective pressure on the malaria parasite in the context of haemoglobinopathies in Africa.

Bisphenol S remodels red blood cell membrane lipids by altering plasma lipid levels, causing the risk of venous thrombosis in SD rats and zebrafish embryos

Bisphenol S (BPS) is a raw material that is used extensively in various manufacturing processes but possesses a high detection rate in human red blood cells (RBCs). Accordingly, BPS is a potential toxicant in disturbing the function of RBCs and causing RBC-related diseases. To date, the effects and mechanisms of BPS-induced RBC-related diseases have not been elucidated. Here, using different models, including rats, zebrafish embryos and RBCs, the underlying mechanism of RBC-related diseases induced by BPS was explored. The accumulation of BPS in tissue was colon > kidney > liver > plasma > testicle > heart > brain in SD rats orally administered BPS (10 and 50 mg/kg bw/day) for 32 days, which was similar in both 10 mg/kg bw/day and 50 mg/kg bw/day group. Rats given BPS orally developed hyperlipidemia and increased RBC membrane cholesterol, as well as changes in RBC morphology and function. Moreover, BPS at the concentrations measured in rats plasma caused oxidative stress and phosphatidylserine exposure in vitro RBCs. These combined factors led to RBC aggregation in blood and an increasing in the number of RBCs in the blood vessels of the liver in rats. The dynamic visual observation of RBCs in vein vessels of zebrafish embryos exposed to BPS at 0, 1, 10 and 100 μg/L further found that the flow of RBCs in the tail vein is slow or even immobile, posing the risk of venous thrombosis. The present study provides new insight into the links between environmental pollutants and venous thrombosis.

[BRAIN FOCAL ISCHEMIA-REPERFUSION CAUSES A DECREASED RESISTANCE OF ERYTHROCYTES FROM VENOUS BLOOD TO ACID HEMOLYSIS, WHICH IS PREVENTED BY ECDYSTERONE]

We investigated the resistance of erythrocytes from rat brain venous blood to acid hemolysis in the dynamics of brain ischemic period (15, 30, 45 and 60 min), as well as in the early (5 min) and distant (24h) period of brain reperfusion. Brain ischemia-reperfusion was made in rats that received ecdysterone (standartized extract of Serratula coronata) within 18 days (per os, 1 mg/kg). Analysis of the kinetic curves of acid hemolysis showed a pronounced (60 times, from 1.45 to 85.85% at 60 min of brain ischemia and at 5 min of brain reperfusion, respectively) increase of unstable erythrocytes that hemolyzed easily (< 2.5 min). In the preconditioned rats, this increase was only 8-fold. During the period of brain ischemia, with a maximum at 15th minute, in the venous blood from brain the diene conjugates (DK) pools increased from 2.40 to 9.48 ng/mg protein and LTC4 pools increased from 1.49 to 5.98 pmol/mg protein. Even more pools of DC and LTC4 were increased at 5th min of brain reperfusion. In animals received ecdysterone, during ischemia and early reperfusion period, both pools of DC and LTC4 in venous blood were lower than that in the controls. The latter implies a possible antiradical mechanism of the protective effect of ecdysterone.

Clozapine induces chloride channel-4 expression through PKA activation and modulates CDK5 expression in SH-SY5Y and U87 cells

OBJECTIVES

Second-generation antipsychotic drugs, such as clozapine, were reported to enhance neurite outgrowth by nerve growth factor in PC12 cells. The authors previously showed that chloride channel 4 (CLC-4) is responsible for nerve growth factor-induced neurite outgrowth in neuronal cells. In this study, we examined whether clozapine induces CLC-4 in neuroblastoma and glioma cells.

METHODS

The effect of clozapine on CLC-4 expression was examined in neuroblastoma (SH-SY5Y) and glioma (U87) cells. To investigate the signaling pathway responsible for clozapine-induced CLC-4 expression, the phosphorylation of cAMP response element-binding protein (CREB), which binds CRE in the promoter of the human CLC-4 gene, was examined. To identify the target of clozapine induced CLC-4, CLC-4 siRNA was introduced to neuroblastoma and glioma cells for functional knockdown.

RESULTS

We observed that clozapine increased CLC-4 expression in both SH-SY5Y and U87 cells. Clozapine induced CREB phosphorylation, but in the presence of inhibitor of protein kinase A (an upstream kinase of CREB) clozapine-induced CLC-4 expression was suppressed. Finally, we found that CLC-4 knockdown suppressed clozapine-induced cyclin-dependent kinase 5 (CDK5) expression in SH-SY5Y and U-87 cells suggesting CDK5 as potential molecular target of clozapine induced CLC-4 expression.

CONCLUSIONS

The results of the present study suggest that clozapine's therapeutic effect may include the induction of CLC-4 which is dependent on CREB activation via PKA. We also found that functional knockdown of CLC-4 resulted in reduction of CDK5 expression, which may also be implicated in clozapine's therapeutic effect.

Eryptosis in lead-exposed workers

Eryptosis is a physiological phenomenon in which old and damaged erythrocytes are removed from circulation. Erythrocytes incubated with lead have exhibited major eryptosis. In the present work we found evidence of high levels of eryptosis in lead exposed workers possibly via oxidation. Blood samples were taken from 40 male workers exposed to lead (mean blood lead concentration 64.8μg/dl) and non-exposed workers (4.2μg/dl). The exposure to lead produced an intoxication characterized by 88.3% less δ-aminolevulinic acid dehydratase (δALAD) activity in lead exposed workers with respect to non-lead exposed workers. An increment of oxidation in lead exposed workers was characterized by 2.4 times higher thiobarbituric acid-reactive substance (TBARS) concentration and 32.8% lower reduced/oxidized glutathione (GSH/GSSG) ratio. Oxidative stress in erythrocytes of lead exposed workers is expressed in 192% higher free calcium concentration [Ca(2+)]i and 1.6 times higher μ-calpain activity with respect to non-lead exposed workers. The adenosine triphosphate (ATP) concentration was not significantly different between the two worker groups. No externalization of phosphatidylserine (PS) was found in non-lead exposed workers (<0.1%), but lead exposed workers showed 2.82% externalization. Lead intoxication induces eryptosis possibly through a molecular pathway that includes oxidation, depletion of reduced glutathione (GSH), increment of [Ca(2+)], μ-calpain activation and externalization of PS in erythrocytes. Identifying molecular signals that induce eryptosis in lead intoxication is necessary to understand its physiopathology and chronic complications.

Role Ca(2+) in mechanisms of the red blood cells microrheological changes

To assess the physiological role of intracellular Ca(2+) in the changes of microrheological red blood cell (RBC) properties (RBC deformability and aggregation), we employed several types of chemicals that can increase and decrease of the intracellular Ca(2+) concentration. The rise of Ca(2+) influx, stimulated by mechanical loading, A23187, thrombin, prostaglandin F(2α) was accompanied by a moderate red cell deformability lowering and an increase of their aggregation. In contrast, Ca(2+) entry blocking into the red cells by verapamil led to a significant RBC aggregation decrease and deformability rise. Similar microrheological changes were observed in the red blood cells treated with phosphodiesterase inhibitors IBMX, vinpocetine, rolipram, pentoxifylline. When forskolin (10 μM), an AC stimulator was added to RBC suspension, the RBC deformability was increased (p <0.05). Somewhat more significant deformability rise appeared after RBC incubation with dB-AMP. Red cell aggregation was significantly decreased under these conditions (p<0.01). On the whole the total data clearly show that the red cell aggregation and deformation changes were connected with an activation of both intracellular signaling pathways: Ca(2+) regulatory mechanism and Gs-protein/adenylyl-cyclase-cAMP system. And the final red cell microrheological regulatory effect is connected with the crosstalk between these systems.

TRPC6 contributes to the Ca(2+) leak of human erythrocytes

Human erythrocytes express cation channels which contribute to the background leak of Ca(2+), Na(+) and K(+). Excessive activation of these channels upon energy depletion, osmotic shock, Cl(-) depletion, or oxidative stress triggers suicidal death of erythrocytes (eryptosis), characterized by cell-shrinkage and exposure of phosphatidylserine at the cell surface. Eryptotic cells are supposed to be cleared from circulating blood. The present study aimed to identify the cation channels. RT-PCR revealed mRNA encoding the non-selective cation channel TRPC6 in erythroid progenitor cells. Western blotting indicated expression of TRPC6 protein in erythrocytes from man and wildtype mice but not from TRPC6(-/-) mice. According to flow-cytometry, Ca(2+) entry into human ghosts prepared by hemolysis in EGTA-buffered solution containing the Ca(2+) indicator Fluo3/AM was inhibited by the reducing agent dithiothreitol and the erythrocyte cation channel blockers ethylisopropylamiloride and amiloride. Loading of the ghosts with antibodies against TRPC6 or TRPC3/6/7 but neither with antibodies against TRPM2 or TRPC3 nor antibodies pre-adsorbed with the immunizing peptides inhibited ghost Ca(2+) entry. Moreover, free Ca(2+) concentration, cell-shrinkage, and phospholipid scrambling were significantly lower in Cl(-)-depleted TRPC6(-/-) erythrocytes than in wildtype mouse erythrocytes. In conclusion, human and mouse erythrocytes express TRPC6 cation channels which participate in cation leak and Ca(2+)-induced suicidal death.

Intracellular free calcium concentration and calcium transport in human erythrocytes of lead-exposed workers

Erythrocytes are the route of lead distribution to organs and tissues. The effect of lead on calcium homeostasis in human erythrocytes and other excitable cells is not known. In the present work we studied the effect of lead intoxication on the uptake and efflux (measured as (Ca(2+)-Mg(2+))-ATPase activity) of calcium were studied in erythrocytes obtained from lead-exposed workers. Blood samples were taken from 15 workers exposed to lead (blood lead concentration 74.4+/-21.9 microg/dl) and 15 non-exposed workers (9.9+/-2 microg/dl). In erythrocytes of lead-exposed workers, the intracellular free calcium was 79+/-13 nM, a significantly higher concentration (ANOVA, P<0.01) than the one detected in control (30+/-9 nM). The enhanced intracellular free calcium was associated with a higher osmotic fragility and with important modifications in erythrocytes shape. The high intracellular free calcium in lead-exposed workers was also related to a 100% increase in calcium incorporation and to 50% reduction of (Ca(2+)-Mg(2+))-ATPase activity. Lipid peroxidation was 1.7-fold higher in erythrocytes of lead-exposed workers as compared with control. The alteration on calcium equilibrium in erythrocytes is discussed in light of the toxicological effects in lead-exposed workers.

Revealing Complex Traits with Small Molecules and Naturally Recombinant Yeast Strains

Here we demonstrate that natural variants of the yeast Saccharomyces cerevisiae are a model system for the systematic study of complex traits, specifically the response to small molecules. As a complement to artificial knockout collections of S. cerevisiae widely used to study individual gene function, we used 314- and 1932-member libraries of mutant strains generated by meiotic recombination to study the cumulative, quantitative effects of natural mutations on phenotypes induced by 23 small-molecule perturbagens (SMPs). This approach reveals synthetic lethality between SMPs, and genetic mapping studies confirm the involvement of multiple quantitative trait loci in the response to two SMPs that affect respiratory processes. The systematic combination of natural variants of yeast and small molecules that modulate evolutionarily conserved cellular processes can enable a better understanding of the general features of complex traits.

Calcium imaging of individual erythrocytes: Problems and approaches

Although in erythrocytes calcium is thought to be important in homeostasis, measurements of this ion concentration are generally seen as rather problematic because of the auto-fluorescence or absorption properties of the intracellular milieu. Here, we describe experiments to assess the usability of popular calcium indicators such as Fura-2, Indo-1 and Fluo-4. In our experiments, Fluo-4 turned out to be the preferable indicator because (i) its excitation and emission properties were least influenced by haemoglobin and (ii) it was the only dye for which excitation light did not lead to significant auto-fluorescence of the erythrocytes. From these results, we conclude that the use of indicators such as Fura-2 together with red blood cells has to be revisited critically. We thus utilized Fluo-4 in erythrocytes to demonstrate a robust but heterogeneous calcium increase in these cells upon stimulation by prostaglandin E(2) and lysophosphatidic acid. For the latter stimulus, we recorded emission spectra of individual erythrocytes to confirm largely unaltered Fluo-4 emission. Our results emphasize that in erythrocytes measurements of intracellular calcium are reliably possible with Fluo-4 and that other indicators, especially those requiring UV-excitation, appear less favourable.

Effect of Escherichia coli hemolysin on permeability of erythrocyte membranes to calcium

The extracellular hemolysin produced by porcine strains of E. coli effects a marked increase in the calcium permeability of erythrocyte membranes. This hemolysin promotes both calcium efflux from either calcium-loaded erythrocytes or erythrocyte ghosts and calcium accumulation during the pre-lytic period. Erythrocyte membrane calcium permeability was determined using either the radioisotope 45Ca or a calcium electrode. When similar concentrations of erythrocytes (35% packed cell volume) were treated with increasing amounts of hemolysin there was an increase in both the rate and the extent of calcium accumulation by the erythrocytes. These increases were due to increased numbers of erythrocytes becoming permeable to calcium as hemolysin concentrations increased, rather than increasing amounts of calcium being accumulated by individual erythrocytes. Hemolysins produced by porcine strains of E. coli from five geographical areas all increased calcium permeability of erythrocyte membranes.

Passive permeability of human red blood cells to calcium

Ca2+ influx was measured into human erythrocytes in which efflux was blocked by either introduction of an intracellular Ca2+ chelator, introduction of the Ca2+ chelator followed by ATP depletion, or depletion of the Ca2+ pump cofactors ATP and Mg2+. The Ca2+ influx under all three conditions was 14-20 mumol . 1 cells-1 . h-1, which is an order of magnitude higher than the influx previously reported for cells depleted of either ATP or Mg2+ separately. The difference between the two values was explained by the finding of substantial Ca2+ efflux from the Ca2+-loaded ATP-depleted cells, whereas this efflux was insignificant from cells loaded with quin 2 and then ATP depleted. Under these latter conditions Ca2+ influx estimates the unidirectional permeability to this cation. Studies using this technique showed that Ca2+ influx was the same in media of isotonic sodium, potassium, lithium, choline, or magnesium chlorides. Moreover the dependence of Ca2+ influx on external Ca2+ concentration was well described by the sum of saturable and nonsaturable (linear) components.