Healthy Human Erythrocytes Research Articles

Asiatic acid impedes NSCLC progression by inhibiting COX-2 and modulating PI3K signaling.

Non-small cell lung cancer comprises up to 85% of lung cancer cases and has a poor prognosis. At present, there are still no effective treatments for this illness. Evidence suggests that the prostaglandin [cyclooxygenase-2 (COX-2)] and leukotriene [lipoxygenase-5 (5-LOX)] pathways are involved in lung cancer carcinogenesis. Therefore, novel agents that target COX-2 and 5-LOX may have therapeutic potential. In the present study, we examined the role of asiatic acid (AA), a triterpenoid saponin, in targeting the protein kinases responsible for lung cancer proliferation and mobility. The experimental data revealed that AA inhibited the growth of lung cancer cells (> 50%) and it significantly impeded the proliferation of lung cancer cells by inhibiting COX-2, which results in downregulation of the phosphotidyl inositol-3 kinase/protein kinase B/mammalian target of rapamycin signaling pathway, leading to an induction of cytotoxic autophagy-mediated apoptosis. Mechanistically, the expression of mitogen-activated protein kinase/extracellular signal-regulated kinase, hypoxia-inducible factor-1 and vascular endothelial growth factor is downregulated by AA, thereby reducing cell mobility and invasion. It also shows negative osmotic fragility on healthy human erythrocytes. It is concluded that AA may be a viable therapeutic drug for non-small cell lung cancer treatment, which opens new opportunities for synthesizing analogues.

Development of erythrocyte-mimetic PFOB/PDMS thermoplastic elastomer core-shell microparticles via SPG membrane emulsification

Erythrocyte-mimetic perfluorooctylbromide (PFOB)/polydimethylsiloxane (PDMS) thermoplastic elastomer core-shell microparticles were fabricated (for the first time) via Shirasu porous glass membrane emulsification (SPG ME) with evaporation-induced phase separation (EIPS). The resulting micro-sized core-shell particles showed a spontaneously concave shape without a subsequent deformation process such as organic solvent immersion or temperature variations. It replicated the healthy human erythrocyte morphology. In addition, their sizes and morphologies could be controlled by varying the pore size and dispersed-phase composition of the SPG membrane. The diameters of the precisely controlled particles were similar to those of human blood cells (9.6 ± 1.9 μm). The microcompression test revealed a high deformability of the particles owing to both softness of the PDMS-TPE shell and their core-shell structure. The PDMS-based materials displayed a high oxygen permeability, and PFOB displayed a high oxygen solubility. Finally, the oxygen transportation function was evaluated using oxygen tension-responsive HeLa cells (hr-HeLa) under hypoxic conditions (5% O2). This demonstrated the effectiveness of PFOB/PDMS-TPE microparticles as artificial oxygen carriers in various biomedical applications such as tissue engineering.

Piperine protects oxidative modifications in human erythrocytes.

Piperine (1-piperoyl piperidine), a major alkaloid constituent of Piper nigrum L. and Piper longum L. has pleiotropic biological effects, but the mechanism(s) involved remain to be elucidated. The current study was conducted to examine the efficacy of antioxidant ability of piperine on t-BHP induced markers of oxidative stress in human erythrocytes. Healthy human erythrocytes and erythrocytes membrane was stressed with free radical inducer chemical; t-BHP (10-5M), and the effects of piperine was measured against free radical mediated modification in lipid and protein content,-SH and GSH value with antioxidant potential. The results demonstrate that treatment of erythrocytes with piperine (10-5 to 10-7M) significantly (p<0.05) ameliorated the adverse consequences of oxidative stress as evidenced by prevention of oxidation of erythrocyte reduced glutathione, membrane thiols, proteins, and peroxidation of lipids; the effects were in correlation with ferric reducing and radical scavenging abilities of piperine. The study concludes that piperine possesses potent anti-oxidant potential which may explain many of its observed biological effects.

Preliminary study of antimicrobial peptide cathelicidin-PY therapy in mice with acute liver failure

Objective: To investigate the feasibility of cationic antimicrobial peptide cathelicidin-PY(PY) therapy through a mouse model of acute liver failure. Methods: The ability of different concentrations of antimicrobial peptide PY to neutralize endotoxin / lipopolysaccharide (LPS) in vitro was detected by Limulus Amebocyte Lysate (LAL) assay. Cell counting kit-8 (CCK-8) was used to detect the toxic effect of different concentrations of antimicrobial peptide PY on mouse monocyte macrophages (RAW264.7). An in vitro hemolysis experiment was used to evaluate the activity of antimicrobial peptide PY on healthy human erythrocytes. D-galactosamine combined with LPS- induced mouse model of acute liver failure was constructed. The antimicrobial peptide PY effect on survival rate of mouse model was observed. HE staining was used to observe the pathological changes of liver tissue. Immunohistochemistry and Western blotting were used to detect the expression of apoptosis-associated protein caspase-3. Intra-group comparisons were performed using t-test and analysis of variance. χ (2) test was used for the comparison of rates. Results: An in vitro experiment showed that the endotoxin neutralization rate was higher at very low dose (0.01 μmol/L), and exceeded 70% at medium-dose (10-40 μmol/L), and the difference between groups with different concentration was statistically significant (F = 569.22, P < 0.05). Medium-dose antimicrobial peptide PY had strong endotoxin neutralizing effect, low cytotoxicity and hemolytic activity. Moreover, in vivo experiments showed that the degree of liver injury and survival rate of mouse model was significantly improved with the medium-dose of antimicrobial peptide PY. Immunohistochemistry results showed that the expression of caspase-3 in the liver tissue was significantly depleted in the medium-dose group than that of the liver failure group, and the results were consistent with protein immunoblotting testing. Conclusion: Antimicrobial peptide PY possesses a strong ability to neutralize endotoxin and few toxic side effects. A specific dose of antimicrobial peptide PY can attenuate hepatocyte apoptosis and significantly improve the survival rate of animal model, and thus provides a new idea for the liver failure treatment.

Efficient Synthesis and Antibacterial Profile of Bis(2-hydroxynaphthalene- 1,4-dione).

Antibacterial resistance is a serious public health problem infecting millions in the global population. Currently, there are few antimicrobials on the market against resistant bacterial infections. Therefore, there is an urgent need for new therapeutic options against these strains. In this study, we synthesized and evaluated ten Bis(2-hydroxynaphthalene-1,4-dione) against Gram-positive strains, including a hospital Methicillin-resistant (MRSA), and Gram-negative strains. The compounds were prepared by condensation of aldehydes and lawsone in the presence of different L-aminoacids as catalysts in very good yields. The compounds were submitted to antibacterial analysis through disk diffusion and Minimal Inhibitory Concentration (MIC) assays. L-aminoacids have been shown to be efficient catalysts in the preparation of Bis(2- hydroxynaphthalene-1,4-dione) from 2-hydroxy-1,4-naphthoquinones and arylaldehydes in excellent yields of up to 96%. The evaluation of the antibacterial profile against Gram-positive strains (Enterococcus faecalis ATCC 29212, Staphylococcus aureus ATCC 25923, S. epidermidis ATCC 12228) also including a hospital Methicillin-resistant S. aureus (MRSA) and Gram-negative strains (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Klebsiella pneumoniae ATCC 4352), revealed that seven compounds showed antibacterial activity within the Clinical and Laboratory Standards Institute (CLSI) levels mainly against P. aeruginosa ATCC 27853 (MIC 8-128 µg/mL) and MRSA (MIC 32-128 µg/mL). In addition, the in vitro toxicity showed all derivatives with no hemolytic effects on healthy human erythrocytes. Furthermore, the derivatives showed satisfactory theoretical absorption, distribution, metabolism, excretion, toxicity (ADMET) parameters, and a similar profile to antibiotics currently in use. Finally, the in silico evaluation pointed to a structure-activity relationship related to lipophilicity for these compounds. This feature may help them in acting against Gram-negative strains, which present a rich lipid cell wall selective for several antibiotics. Our data showed the potential of this series for exploring new and more effective antibacterial activities in vivo against other resistant bacteria.

Intracellular Ca2+ Concentration and Phosphatidylserine Exposure in Healthy Human Erythrocytes in Dependence on in vivo Cell Age.

After about 120 days of circulation in the blood stream, erythrocytes are cleared by macrophages in the spleen and the liver. The “eat me” signal of this event is thought to be the translocation of phosphatidylserine from the inner to the outer membrane leaflet due to activation of the scramblase, while the flippase is inactivated. Both processes are triggered by an increased intracellular Ca2+ concentration. Although this is not the only mechanism involved in erythrocyte clearance, in this minireview, we focus on the following questions: Is the intracellular-free Ca2+ concentration and hence phosphatidylserine exposure dependent on the erythrocyte age, i.e. is the Ca2+ concentration, progressively raising during the erythrocyte aging in vivo? Can putative differences in intracellular Ca2+ and exposure of phosphatidylserine to the outer membrane leaflet be measured in age separated cell populations? Literature research revealed less than dozen of such publications with vastly contradicting results for the Ca2+ concentrations but consistency for a lack of change for the phosphatidylserine exposure. Additionally, we performed reanalysis of published data resulting in an ostensive illustration of the situation described above. Relating these results to erythrocyte physiology and biochemistry, we can conclude that the variation of the intracellular free Ca2+ concentration is limited with 10 μM as the upper level of the concentration. Furthermore, we propose the hypothesis that variations in measured Ca2+ concentrations may to a large extent depend on the experimental conditions applied but reflect a putatively changed Ca2+ susceptibility of erythrocytes in dependence of in vivo cell age.

Пластифицированные плёнки на основе сукцинила хитозана

The article is devoted to the development of new approaches to the creation of modern wound healing highly elastic films with good hemocompatibility based on a water-soluble chitosan derivative – the succinyl of chitosan. These trips are based on the use of plasticizers. It was established that chitosan succinyl, in contrast to chitosan, is capable of exhibiting insignificant forced-elastic deformation, but still not sufficient to use unmodified films based on it as wound healing coatings. The deformation-strength properties of the films were studied on a universal tensile testing machine. The tensile stress (σ) was determined taking into account the cross-sectional area of the sample taken for testing, and expressed in MPa. The elongation at break (ε) was calculated taking into account the initial length of the film sample taken for testing, and expressed as a percentage. The values of elongation at break and tensile stress were calculated as the arithmetic average of five parallel measurements. The hemocompatibility of chitosan-glycerol succinyl systems was evaluated by determining the osmotic resistance of healthy human erythrocytes using a unified method in the modification of L.I. Idelson. It is shown that the introduction of glycerol as a plasticizer in the process of film formation leads to a significant improvement in their physical and mechanical characteristics. An increase in the glycerol content in the film up to 50 wt% is accompanied by a significant increase in tensile elongation. The value of the breaking stress in this case, naturally decreases. But, since the value of the breaking stress in any case remains at the level of the necessary values, the observed drop in strength indicators is not fundamental. The stabilizing effect of the succinyl of chitosan-glycerin systems on cell membranes under physiological conditions is proved, which suggests their high hemocompatibility.

Liposomal-delivery of phosphodiesterase 5 inhibitors augments UT-15C-stimulated ATP release from human erythrocytes

The use of liposomes to affect targeted delivery of pharmaceutical agents to specific sites may result in the reduction of side effects and an increase in drug efficacy. Since liposomes are delivered intravascularly, erythrocytes, which constitute almost half of the volume of blood, are ideal targets for liposomal drug delivery.In vivo, erythrocytes serve not only in the role of oxygen transport but also as participants in the regulation of vascular diameter through the regulated release of the potent vasodilator, adenosine triphosphate (ATP). Unfortunately, erythrocytes of humans with pulmonary arterial hypertension (PAH) do not release ATP in response to the physiological stimulus of exposure to increases in mechanical deformation as would occur when these cells traverse the pulmonary circulation. This defect in erythrocyte physiology has been suggested to contribute to pulmonary hypertension in these individuals.In contrast to deformation, both healthy human and PAH erythrocytes do release ATP in response to incubation with prostacyclin analogs via a well-characterized signaling pathway. Importantly, inhibitors of phosphodiesterase 5 (PDE5) have been shown to significantly increase prostacyclin analog-induced ATP release from human erythrocytes.Here we investigate the hypothesis that targeted delivery of PDE5 inhibitors to human erythrocytes, using a liposomal delivery system, potentiates prostacyclin analog- induced ATP release. The findings are consistent with the hypothesis that directed delivery of this class of drugs to erythrocytes could be a new and important method to augment prostacyclin analog-induced ATP release from these cells. Such an approach could significantly limit side effects of both classes of drugs without compromising their therapeutic effectiveness in diseases such as PAH.

Anti-fungal activity of Ctn[15-34], the C-terminal peptide fragment of crotalicidin, a rattlesnake venom gland cathelicidin.

Crotalicidin (Ctn), a 34-residue cathelicidin from a South American rattlesnake, and its fragment (Ctn[15-34]) have shown anti-infective and cytotoxic activities against Gram-negative bacteria and certain tumor lines, respectively. The extent of such effects has been related to physicochemical characteristics such as helicity and hydrophobicity. We now report the anti-fungal activity of Ctn and its fragments (Ctn[1-14]) and (Ctn[15-34]). MIC determination and luminescent cell viability assays were used to evaluate the anti-infective activity of Ctn and its fragments (Ctn[1-14]) and (Ctn[15-34]) as anti-fungal agents against opportunistic yeast and dermatophytes. Cytotoxicity towards healthy eukaryotic cells was assessed in vitro with healthy human kidney-2 (HK-2) cells and erythrocytes. The checkerboard technique was performed to estimate the effects of combining either one of the peptides with amphotericin B. Ctn was the most active peptide against dermatophytes and also the most toxic to healthy eukaryotic cells. Fragments Ctn[1-14] and Ctn[15-35] lost activity against dermatophytes, but became more active against pathogenic yeasts, including several Candida species, both clinical isolates and standard strains, with MICs as low as 5 μm. Interestingly, the two peptide fragments were less cytotoxic to healthy HK-2 cells and less hemolytic to human erythrocytes than the standard-of-care amphotericin B. Also noteworthy was the synergy between Ctn peptides and amphotericin B, with consequent reduction in MICs of both drug and peptides. Altogether, Ctn and its fragments, particularly Ctn[15-34], are promising leads, either alone or in combined regimen with amphotericin B, for the treatment of fungal diseases.

Synthesis and biological evaluation of 2-arylimino-3-pyridin-thiazolineone derivatives as antibacterial agents

With an intention to find more potent antibacterial agents, four halogen disubstituted thiazolineone derivatives (2a–d), five halogen monosubstituted thiazolineone derivatives (2e–i), and eleven 2-arylimino-3-pyridin-thiazolineone derivatives (2j–t) were synthesized and screened for their antibacterial activity, bactericidal activity, cytotoxicity, and erythrocyte hemolysis. Most of the synthesized derivatives showed antibacterial activity in inhibiting the growth of S. epidermidis and MRSA, and exhibited safety in the cytotoxicity study on the Vero cells and hemolytic activities test on healthy human erythrocytes. 2-Arylimino-3-pyridin-thiazolineone derivatives not only improved the clog P, but also showed potent antibacterial activity in inhibiting the growth of S. epidermidis and MRSA. In particularly, several compounds (2f, 2i, 2r and 2t) showed bactericidal activity, in which compound 2r displayed the best inhibitory capacity among the synthesized compounds, and further druggability research is on going.

Highly Selective Fluorescence Determination of the Hematin Level in Human Erythrocytes with No Need for Separation from Bulk Hemoglobin

Hematin-induced fluorescence quenching of boron-doped graphene quantum dots (BGQDs) allows for determination of hematin concentration in human erythrocytes with no need for separating hematin from hemoglobin before performing the assay. The BGQDs are made by oxidizing a graphite anode by holding the voltage between a graphite rod and a Pt cathode at 3 V for 2 h in an aqueous borax solution at pH 7; then, the borate solution was filtered with BGQDs, and the borate was dialyzed from the filtrate, leaving a solution of BGQDs in water. The fluorescence intensity of BGQDs is measurable in real time, and its quenching is very sensitive to the concentration of hematin in the system but not to other coexisting biological substances. The analytical signal is defined as ΔF = 1 - F/F0, where F0 and F are the fluorescence intensities of the BGQDs before and after interaction with hematin, respectively. There is a good linear relationship between ΔF and hematin concentration, ranging from 0.01 to 0.92 μM, with the limit of detection (LOD) being ∼0.005 ± 0.001 μM at a signal-to-noise ratio of 3. This new method is sensitive, label-free, simple, and inexpensive, and many tedious procedures related to sample separation and preparation can be omitted, implying that this method has potential for applications in clinical examinations and disease diagnoses. For example, the determination of the hematin levels in two kind of red blood cell samples, healthy human and sickle cell erythrocytes, gives average concentrations of hematin of ∼(23.1 ± 4.9) μM (average of five samples) for healthy red cell cytosols and ∼(52.5 ± 9.5) μM (average of two samples) for sickle red cell cytosols.

Biological evaluation of the toxicity and the cell cycle interruption by some benzimidazole derivatives

In this work, the in vitro tests of biological activity of benzimidazoles were conducted. This group of benzimidazole derivatives was evaluated as potential bioreductive agents and their characteristic pro-apoptosis activity and cell cycle interruption on the human lung adenocarcinoma A549 cells were discussed. Their toxicity on the healthy human erythrocytes and their influence on the healthy human erythrocytes acetylcholinesterase enzyme (AChE) were established. Their apoptosis activity on A549 cells line was determined by Annexin V-APC test, and it was visualized by Hoechst test. In the next stage, their influence on the cell cycle interruption was determined by using the ribonuclease reagent. The AChE inhibition test was defined by the Ellman method, and the red blood cell lysis was defined by erythrotoxicity test. The results proved the pro-apoptosis properties of all tested compounds in normoxia and hypoxia. The DNA content assay showed that the benzimidazoles possess the ability to interrupt S phase of tumor cell cycle. The best activity in this action was presented by compound 1, especially in hypoxia, and it proves that the N-oxide analogs are predispositioned to the hypoxic target. In this study, the benzimidazoles were found as potentially biocompatible and their inhibition of acetylcholinesterase was lower than tirapazamine and much lower than tacrine which constitutes their desired effect of potential biological activity.

Signalling mechanisms involved in C‐peptide‐mediated inhibition of low O2‐induced ATP release from human erythrocytes

Background and objectivesIn vivo, insulin is released with connecting peptide (C‐peptide) which has recently been shown to have biological activity. When erythrocytes are exposed to reduced oxygen (O2) tension, they release O2 as well as the vasodilator ATP enabling them to participate in the appropriate distribution of vascular perfusion and, thereby, O2 supply. Low O2‐induced ATP release is absent in erythrocytes of humans with type 2 diabetes (DM2), but this response is restored by co‐administration of physiological concentrations of insulin and C‐peptide. However, either C‐peptide or insulin, when administered alone, inhibits low O2‐induced ATP release from healthy human erythrocytes. Here, we investigated the mechanism(s) by which C‐peptide inhibits this physiological ATP release from human erythrocytes.MethodsErythrocytes from healthy humans (n = 21) or humans with DM2 (n = 4) were incubated with C‐peptide in the absence or presence of inhibitors of either protein kinase C alpha (PKCα) or soluble guanylyl cyclase (sGC). Erythrocytes were then exposed to low O2, and ATP release was determined.ResultsIn healthy human erythrocytes, C‐peptide inhibited ATP release in response to low O2. Preincubation with either Gö6976, a PKCα inhibitor, or ODQ, a sGC inhibitor, prevented this effect of C‐peptide. In addition, C‐peptide alone did not rescue low O2‐induced ATP release from DM2 erythrocytes.ConclusionAdministration of C‐peptide in excess of levels present under physiological conditions or the combination of C‐peptide and insulin at ratios that exceed those observed physiologically to insulin‐deficient individuals can be detrimental for low O2‐induced ATP release from human erythrocytes and could, consequently, interfere with optimal O2 delivery to skeletal muscle.

The free heme concentration in healthy human erythrocytes

Heme, the prosthetic group of hemoglobin, may be released from its host due to an intrinsic instability of hemoglobin and accumulate in the erythrocytes. Free heme is in the form of hematin (Fe3+ protoporphyrin IX OH) and follows several pathways of biochemical toxicity to tissues, cells, and organelles since it catalyzes the production of reactive oxygen species. To determine concentration of soluble free heme in human erythrocytes, we develop a new method. We lyse the red blood cells and isolate free heme from hemoglobin by dialysis. We use the heme to reconstitute horseradish peroxidase (HRP) from an excess of the apoenzyme and determine the HRP reaction rate from the evolution of the emitted luminescence. We find that in a population of five healthy adults the average free heme concentration in the erythrocytes is 21±2μM, ca. 100× higher than previously determined. Tests suggest that the lower previous value was due to the use of elevated concentrations of NaCl, which drive hematin precipitation and re-association with apoglobin. We show that the found hematin concentration is significantly higher than estimates based on equilibrium release and the known hematin dimerization. The factors that lead to enhanced heme release remain an open question.

Dietary indicaxanthin from cactus pear (Opuntia ficus-indica L. Mill) fruit prevents eryptosis induced by oxysterols in a hypercholesterolaemia-relevant proportion and adhesion of human erythrocytes to endothelial cell layers.

Toxic oxysterols in a hypercholesterolaemia-relevant proportion cause suicidal death of human erythrocytes or eryptosis. This process proceeds through early production of reactive oxygen species (ROS), release of prostaglandin (PGE2) and opening of PGE2-dependent Ca channels, membrane phosphatidylserine (PS) externalisation, and cell shrinkage. The present study was the first to reveal that a bioavailable phytochemical, indicaxanthin (Ind) from cactus pear fruit, in a concentration range (1.0-5.0 μM) consistent with its plasma level after a fruit meal, prevents PS externalisation and cell shrinkage in a dose-dependent manner when incubated with isolated healthy human erythrocytes exposed to an oxysterol mixture for 48 h. Dietary Ind inhibited ROS production, glutathione (GSH) depletion, PGE2 release and Ca2+ entry. Ind alone did not modify the erythrocyte redox environment or affect other parameters. Ex vivo spiking of normal human blood with the oxysterol mixture for 48 h induced eryptosis, resulting in the production of ROS and decreased levels of GSH, which was prevented by concurrent exposure to 5 μm-Ind. The adherence of eryptotic erythrocytes to the endothelium causes vascular tissue injury. Erythrocytes isolated from blood incubated with the oxysterol mixture plus 5 μm-Ind did not adhere to endothelial cell monolayers. Eryptotic erythrocytes may contribute to thrombotic complications in hypercholesterolaemia. Our findings suggest the positive effects of diets containing Ind on erythrocytes in hypercholesterolaemic subjects.

Modeling of Vesiculation in Healthy and Defective Human Erythrocyte Membrane

We apply a two-component coarse-grained molecular dynamics (CGMD) red blood cell (RBC) membrane model which includes an explicit representation of the spectrin network, the lipid bilayer, and the band-3 proteins, to simulate vesiculation in the RBC membrane. We investigate vesiculation induced by the spontaneous curvature of the membrane domain and vesiculation induced by a stiffened cytoskeleton causing compression on the lipid bilayer. In addition, we model vesiculation in RBCs from patients suffering from the blood disorders of hereditary spherocytosis (HS) and elliptocytosis (HE). Our simulation results show that the spontaneous curvature of a membrane domain induces vesicles with a diameter less than 50 nm. We also found that compression on the membrane can cause the formation of vesicles having heterogeneous composition with a size similar to the size of the cytoskeleton corral. When both effects are taken into consideration, the compression on the membrane can facilitate the formation of vesicles originated from the membrane domain with the same spontaneous curvature. While the size of the vesicles induced by the compression in the normal RBC membrane is similar to the cytoskeleton corral size, the vesicle sizes become more diverse in HS RBCs because the constrain from the cytoskeleton on the lipid bilayer is reduced. When the vertical connectivity between the lipid bilayer and the cytoskeleton is elevated, multiple vesicles, with sizes similar to the cytoskeleton corral dimension, are generated from the compressed membrane. However, membrane with low vertical connectivity tends to produce larger vesicles under the same compression ratio as above. In HE RBCs, the reduced cytoskeleton connectivity facilitates the membrane vesiculation. It is noted that vesicles released from the HE RBCs could contain spectrin filaments while vesicles released from the HS RBCs are depleted of cytoskeleton components.

Phosphodiesterase 5 inhibitors augment UT-15C-stimulated ATP release from erythrocytes of humans with pulmonary arterial hypertension.

Both prostacyclin analogs and phosphodiesterase 5 (PDE5) inhibitors are effective treatments for pulmonary arterial hypertension (PAH). In addition to direct effects on vascular smooth muscle, prostacyclin analogs increase cAMP levels and ATP release from healthy human erythrocytes. We hypothesized that UT-15C, an orally available form of the prostacyclin analog, treprostinil, would stimulate ATP release from erythrocytes of humans with PAH and that this release would be augmented by PDE5 inhibitors. Erythrocytes were isolated and the effect of UT-15C on cAMP levels and ATP release were measured in the presence and absence of the PDE5 inhibitors, zaprinast or tadalafil. In addition, the ability of a soluble guanylyl cyclase inhibitor to prevent the effects of tadalafil was determined. Erythrocytes of healthy humans and humans with PAH respond to UT-15C with increases in cAMP levels and ATP release. In both groups, UT-15C-induced ATP release was potentiated by zaprinast and tadalafil. The effect of tadalafil was prevented by pre-treatment with an inhibitor of soluble guanylyl cyclase in healthy human erythrocytes. Importantly, UT-15C-induced ATP release was greater in PAH erythrocytes than in healthy human erythrocytes in both the presence and the absence of PDE5 inhibitors. The finding that prostacyclin analogs and PDE5 inhibitors work synergistically to enhance release of the potent vasodilator ATP from PAH erythrocytes provides a new rationale for the co-administration of these drugs in this disease. Moreover, these results suggest that the erythrocyte is a novel target for future drug development for the treatment of PAH.

Low O2-induced ATP release from erythrocytes of humans with type 2 diabetes is restored by physiological ratios of C-peptide and insulin.

ATP release from erythrocytes in response to reduced oxygen (O2) tension stimulates local vasodilation, enabling these cells to direct perfusion to areas in skeletal muscle in need of O2. Erythrocytes of humans with type 2 diabetes do not release ATP in response to low O2. Both C-peptide and insulin individually inhibit low O2-induced ATP release from healthy human erythrocytes, yet when coadministered at physiological concentrations and ratios, no inhibition is seen. Here, we determined: that 1) erythrocytes of healthy humans and humans with type 2 diabetes possess a C-peptide receptor (GPR146), 2) the combination of C-peptide and insulin at physiological ratios rescues low O2-induced ATP release from erythrocytes of humans with type 2 diabetes, 3) residual C-peptide levels reported in humans with type 2 diabetes are not adequate to rescue low O2-induced ATP release in the presence of 1 nM insulin, and 4) the effects of C-peptide and insulin are neither altered by increased glucose levels nor explained by changes in erythrocyte deformability. These results suggest that the addition of C-peptide to the treatment regimen for type 2 diabetes could have beneficial effects on tissue oxygenation, which would help to ameliorate the concomitant peripheral vascular disease.

Simvastatin and GGTI-2133, a geranylgeranyl transferase inhibitor, increase erythrocyte deformability but reduce low O2tension-induced ATP release

Statin drugs inhibit 3-hydroxy-3-methylglutaryl CoA reductase, which reduces the synthesis of both cholesterol and isoprenoids (geranylgeranyl pyrophosphate and farnesyl pyrophosphate), with the latter being lipid molecules responsible for the posttranslational modification of small GTP-binding proteins such as Rho. Effects of statins, independent of lowering blood cholesterol levels, are thought to occur by inhibition of Rho/Rho kinase. The Rho kinase inhibitor Y-27632 has been reported to increase both erythrocyte deformability and low O2 tension-induced ATP release. Here, we tested the hypothesis that by inhibiting Rho/Rho kinase, simvastatin would increase both erythrocyte deformability and low O2 tension-induced ATP release. Male Sprague-Dawley rats were divided into two groups, control or simvastatin treated [simvastatin-supplemented chow (0.02%)], for 4 wk. Simvastatin treatment increased rat erythrocyte deformability compared with controls (n = 6, P < 0.05). However, erythrocytes of simvastatin-treated rats (n = 9, P < 0.05) exhibited impaired low O2 tension-induced ATP release. Similarly, the geranylgeranyl transferase inhibitor GGTI-2133 (10 μM) also increased deformability and impaired low O2 tension-induced ATP release in healthy human erythrocytes (P < 0.05). Interestingly, ATP release in response to mastoparan 7 (n = 7, P < 0.05), which directly activates Gi, and isoproterenol (n = 5, P < 0.05), which signals through Gs, was not altered by incubation with GGTI-2133. These results suggest that although statins increase erythrocyte deformability, likely by inhibiting geranylgeranylation, the finding that both statins and a geranylgeranyl transferase inhibitor attenuated low O2 tension-induced ATP release demonstrates that factors in addition to erythrocyte deformability are critical for ATP release in response to this physiological stimulus.

Toward a Multiscale Description of Microvascular Flow Regulation: O2-Dependent Release of ATP from Human Erythrocytes and the Distribution of ATP in Capillary Networks

Integration of the numerous mechanisms that have been suggested to contribute to optimization of O2 supply to meet O2 need in skeletal muscle requires a systems biology approach which permits quantification of these physiological processes over a wide range of length scales. Here we describe two individual computational models based on in vivo and in vitro studies which, when incorporated into a single robust multiscale model, will provide information on the role of erythrocyte-released ATP in perfusion distribution in skeletal muscle under both physiological and pathophysiological conditions. Healthy human erythrocytes exposed to low O2 tension release ATP via a well characterized signaling pathway requiring activation of the G-protein, Gi, and adenylyl cyclase leading to increases in cAMP. This cAMP then activates PKA and subsequently CFTR culminating in ATP release via pannexin 1. A critical control point in this pathway is the level of cAMP which is regulated by pathway-specific phosphodiesterases. Using time constants (~100 ms) that are consistent with measured erythrocyte ATP release, we have constructed a dynamic model of this pathway. The model predicts levels of ATP release consistent with measurements obtained over a wide range of hemoglobin O2 saturations (sO2). The model further predicts how insulin, at concentrations found in pre-diabetes, enhances the activity of PDE3 and reduces intracellular cAMP levels leading to decreased low O2-induced ATP release from erythrocytes. The second model, which couples O2 and ATP transport in capillary networks, shows how intravascular ATP and the resulting conducted vasodilation are affected by local sO2, convection and ATP degradation. This model also predicts network-level effects of decreased ATP release resulting from elevated insulin levels. Taken together, these models lay the groundwork for investigating the systems biology of the regulation of microvascular perfusion distribution by erythrocyte-derived ATP.