Inhibitory effect of dipyridamole and its derivatives on lipid peroxidation in mitochondria

Erythroid anion transport, nitric oxide, and blood pressure

Glycophorin A and glycophorin B are structural membrane glycoproteins bound in the band 3 multiprotein complexes on human red blood cells (RBCs). Band 3 is an erythroid-specific anion exchanger (AE1). AE1-mediated HCO3 - transport provides the substrate for the enzyme-catalyzed conversion HCO3 - (aq) ⇌ CO2(g), which takes place inside the RBCs. Bicarbonate transport via AE1 supports intravascular acid-base homeostasis and respiratory excretion of CO2. In the past decade, we conducted several comparative physiology studies on Taiwanese people having the glycophorin variant GPMur RBC type (which accompanies greater AE1 expression). We found that increased anion transport across the erythrocyte membrane not only enhances gas exchange and lung functions but also elevates blood pressure (BP) and reduces nitric oxide (NO)-dependent vasodilation and exhaled NO fraction (FeNO) in healthy individuals with GP.Mur. Notably, in people carrying the GPMur blood type, the BP and NO-dependent, flow-mediated vasodilation (FMD) are both more strongly correlated with individual hemoglobin (Hb) levels. As blood NO and nitrite (NO2 -) are predominantly scavenged by intraerythrocytic Hb, and NO2 - primarily enters RBCs via AE1, could a more monoanion-permeable RBC membrane (i.e., GPMur/increased AE1) enhance NO2 -/NO3 - permeability and Hb scavenging of NO2 - and NO to affect blood pressure? In this perspective, a working model is proposed for the potential role of AE1 in intravascular NO availability, blood pressure, and clinical relevance.

Ivermectin and curcumin cause plasma membrane rigidity in Leishmania amazonensis due to oxidative stress

Spin label electron paramagnetic resonance (EPR) spectroscopy was used to study the mechanisms of action of ivermectin and curcumin against Leishmania (L.) amazonensis promastigotes. EPR spectra showed that treatment of the parasites with both compounds results in plasma membrane rigidity due to oxidative processes. With the IC₅₀ and EPR measurements for assays using different parasite concentrations, estimations could be made for the membrane-water partition coefficient (K_M/W), and the concentration of the compound in the membrane (c_m50) and in the aqueous phase (c_w50), which inhibits cell growth by 50%. The K_M/W values indicated that ivermectin has a greater affinity than curcumin for the parasite membrane. Therefore, the activity of ivermectin was higher for experiments with low cell concentrations, but for concentrations greater than 1.5 × 10⁸ parasites/mL the compounds did not show significantly different results. The c_m50 values indicated that the concentration of compound in the membrane leading to growth inhibition or membrane alteration is approximately 1 M for both ivermectin and curcumin. This high membrane concentration suggests that many ivermectin molecules per chlorine channel are needed to cause an increase in chlorine ion influx.

Effect of Dipyridamole on Membrane Energization and Energy Transfer in Chromatophores of Rba. sphaeroides

Effect of dipyridamole (DIP) at concentrations up to 1 mM on fluorescent characteristics of light-harvesting complexes LH2 and LH1, as well as on conditions of photosynthetic electron transport chain in the bacterial chromatophores of Rba. sphaeroides was investigated. DIP was found to affect efficiency of energy transfer from the light-harvesting complex LH2 to the LH1-reaction center core complex and to produce the long-wavelength ("red") shift of the absorption band of light-harvesting bacteriochlorophyll molecules in the IR spectral region at 840-900 nm. This shift is associated with the membrane transition to the energized state. It was shown that DIP is able to reduce the photooxidized bacteriochlorophyll of the reaction center, which accelerated electron flow along the electron transport chain, thereby stimulating generation of the transmembrane potential on the chromatophore membrane. The results are important for clarifying possible mechanisms of DIP influence on the activity of membrane-bound functional proteins. In particular, they might be significant for interpreting numerous therapeutic effects of DIP.

Plasma membrane rigidity effects of 4-hydroxy-2-nonenal in Leishmania, erythrocyte and macrophage

4-hydroxy-2-nonenal (HNE) is a reactive aldehyde produced by cells under conditions of oxidative stress, which has been shown to react with proteins and phosphatidylethanolamine in biological membranes. Using electron paramagnetic resonance (EPR) spectroscopy of a spin label it was demonstrated that 2 h of treatment with HNE causes membrane rigidity in promastigotes of Leishmania (L.) amazonensis, J774.A1 macrophages and erythrocytes. Remarkable fluidity-reducing effects on the parasite membrane were observed at HNE concentrations approximately 4-fold lower than in the case of erythrocyte and macrophage membranes. Autofluorescence of the parasites in PBS suspension (1 × 10⁷ cell/mL) with excitation at 354 nm showed a linear increase of intensity in the range of 400 to 600 nm over 3 h after treatment with 30 μM HNE. Parasite ghosts prepared after this period of HNE treatment showed a high degree of membrane rigidity. Bovine serum albumin (BSA) in PBS treated with HNE for 2 h showed an increase in molecular dynamics and suffered a decrease in its ability to bind a lipid probe. In addition, the antiproliferative activity of L. amazonensis promastigotes, macrophage cytotoxicity and hemolytic potential were assessed for HNE. An IC₅₀ of 24 μM was found, which was a concentration > 10 times lower than the cytotoxic and hemolytic concentrations of HNE. These results indicate that the action of HNE has high selectivity indices for the parasite as opposed to the macrophage and erythrocyte.

Membrane dynamics in Leishmania amazonensis and antileishmanial activities of β-carboline derivatives

Two β-carboline compounds, 8i and 6d, demonstrated in vitro antileishmanial activity against Leishmania (L.) amazonensis promastigotes similar to that of miltefosine (MIL). Estimates of the membrane-water partition coefficient (K_M/W) and the compound concentrations in the membrane (c_m50) and aqueous phase (c_w50) for half maximal inhibitory concentration were made. Whereas these biophysical parameters for 6d were not significantly different from those reported for MIL, 8i showed lower affinity for the parasite membrane (lower K_M/W) and a lower concentration of the compound in the membrane required to inhibit the growth of the parasite (lower c_m50). A 2-hour treatment of Leishmania promastigotes with the compounds 8i and 6d caused membrane rigidity in a concentration-dependent manner, as demonstrated by the electron paramagnetic resonance (EPR) technique and spin label method. This increased rigidity of the membrane was interpreted to be associated with the occurrence of cross-linking of oxidized cytoplasmic proteins to the parasite membrane skeleton. Importantly, the two β-carboline-oxazoline derivatives showed low hemolytic action, both in experiments with isolated red blood cells or with whole blood, denoting their great Leishmania/erythrocyte selectivity index. Using electron microscopy, changes in the membrane of both the amastigote and promastigote form of the parasite were confirmed, and it was demonstrated that compounds 8i and 6d decreased the number of amastigotes in infected murine macrophages. Furthermore, 8i and 6d were more toxic to the protozoa than to J774A.1 macrophages, with treated promastigotes exhibiting a decrease in cell volume, mitochondrial membrane potential depolarization, accumulation of lipid bodies, increased ROS production and changes in the cell cycle.

Influence of oxidized lipids on palmitoyl-oleoyl-phosphatidylcholine organization, contribution of Langmuir monolayers and Langmuir-Blodgett films

In this work, we studied the interaction of two oxidized lipids, PoxnoPC and PazePC, with POPC phospholipid. Mean molecular areas obtained from (π-A) isotherms of mixed PoxnoPC-POPC and PazePC-POPC monolayers revealed different behaviors of these two oxidized lipids: the presence of PoxnoPC in the monolayers induces their expansion, mean molecular areas being higher than those expected in the case of ideal mixtures. PazePC-POPC behave on the whole ideally. This difference can be explained by a different conformation of oxidized lipids. Moreover the carboxylic function of PazePC is protonated under our experimental conditions, as shown by (π-A) isotherms of PazePC at different pH values. Both oxidized lipids induce also an increase of the monolayer elasticity, PoxnoPC being slightly more efficient than PazePC. These monolayers were transferred from the air-water interface onto mica supports for a study by AFM. AFM images are on the whole homogenous, suggesting the presence of only one lipid phase in both cases. However, in the case of PazePC-POPC monolayers, AFM images show also the presence of areas thicker of 7nm to 10nm than the surrounding lipid phase, probably due to the local formation of multilayer systems induced by compression.

Antiulcer activity and subacute toxicity of trans-dehydrocrotonin from Croton cajucara

The antiulcerogenic activity of trans-dehydrocrotonin (DHC), a nor-clerodane diterpene isolated from Croton cajucara Benth. (Euphorbiaceae), and its subacute (35 days) toxicity were studied in mice and rats, respectively. For the antiulcerogenic tests, models of gastric ulcers induced in mice by ethanol/HCl or stress were used. In both models, an oral dose of DHC (100 mg/kg) significantly reduced (P <0.01) the formation of gastric lesions. DHC was also tested for its ability to scavenge free radicals, but no such action was observed in rat liver mitochondria. To assess the subacute toxicity, rats were treated orally with DHC (25, 50 and 100 mg/kg) for 5 weeks. A significant increase in liver weight was observed in male and female rats at highest doses, whereas a significant reduction in plasma alkaline phosphatase and cholesterol levels and an increase in gamma glutamyl transpeptidase were observed only at the highest dose (100 mg/kg) in female rats. DHC caused histopathological alterations in the liver that included a turbid tumefaction, microvacuolar degeneration and nuclear alterations. Despite the beneficial antiulcerogenic activity of DHC, our results suggest that the long-term use of this compound may induce liver damage.

Cell death in amastigote forms of Leishmania amazonensis induced by parthenolide

Background

Leishmania amazonensis infection results in diverse clinical manifestations: cutaneous, mucocutaneous or visceral leishmaniasis. The arsenal of drugs available for treating Leishmania infections is limited. Therefore, new, effective, and less toxic leishmaniasis treatments are still needed. We verified cell death in amastigote forms of Leishmania amazonensis induced by the sesquiterpene lactone parthenolide.

Results

The tested compound was able to concentration-dependently affect axenic and intracellular amastigotes, with IC₅₀ values of 1.3 μM and 2.9 μM, respectively after 72 h incubation. No genotoxic effects were observed in a micronucleus test in mice. Parthenolide induced morphological and ultrastructural changes in axenic amastigotes, including a loss of membrane integrity, swelling of the mitochondrion, cytoplasmic vacuoles, and intense exocytic activity in the region of the flagellar pocket. These results led us to investigate the occurrence of autophagic vacuoles with monodansylcadaverine and the integrity of the plasma membrane and mitochondrial membrane potential using flow cytometry. In all of the tests, parthenolide had positive results.

Conclusions

Our results indicate that the antileishmanial action of parthenolide is associated with autophagic vacuole appearance, a reduction of fluidity, a loss of membrane integrity, and mitochondrial dysfunction. Considering the limited repertoire of existing antileishmanial compounds, the products derived from medicinal plants has been one the greatest advances to help develop new chemotherapeutic approaches.

Antioxidant effect of 4-nerolidylcatechol and α-tocopherol in erythrocyte ghost membranes and phospholipid bilayers

4-Nerolidylcatechol (4-NC) is found in Pothomorphe umbellata root extracts and is reported to have a topical protective effect against UVB radiation-induced skin damage, toxicity in melanoma cell lines, and antimalarial activity. We report a comparative study of the antioxidant activity of 4-NC and α-tocopherol against lipid peroxidation initiated by two free radical-generating systems: 2,2′-azobis(2-aminopropane) hydrochloride (AAPH) and FeSO₄/H₂O₂, in red blood cell ghost membranes and in egg phosphatidylcholine (PC) vesicles. Lipid peroxidation was monitored by membrane fluidity changes assessed by electron paramagnetic resonance spectroscopy of a spin-labeled lipid and by the formation of thiobarbituric acid-reactive substances. When lipoperoxidation was initiated by the hydroxyl radical in erythrocyte ghost membranes, both 4-NC and α-tocopherol acted in a very efficient manner. However, lower activities were observed when lipoperoxidation was initiated by the peroxyl radical; and, in this case, the protective effect of α-tocopherol was lower than that of 4-NC. In egg PC vesicles, malondialdehyde formation indicated that 4-NC was effective against lipoperoxidation initiated by both AAPH and FeSO₄/H₂O₂, whereas α-tocopherol was less efficient in protecting against lipoperoxidation by AAPH, and behaved as a pro-oxidant for FeSO₄/H₂O₂. The DPPH (2,2-diphenyl-1-picrylhydrazyl) free-radical assay indicated that two free radicals were scavenged per 4-NC molecule, and one free radical was scavenged per α-tocopherol molecule. These data provide new insights into the antioxidant capacity of 4-NC, which may have therapeutic applications for formulations designed to protect the skin from sunlight irradiation.

Proton-coupled electron-transfer mechanism for the radical scavenging activity of cardiovascular drug dipyridamole

Dipyridamole (DIP) is a well-known pharmaceutical drug used as a coronary vasodilator and anti-platelet agent in clinics for treating several cardiovascular diseases. Primarily, the therapeutic effects of the drug are attributed to its antioxidant potency. In this research, we aim to declare the unknown antioxidant mechanism of DIP as well as its potent chain-breaking antioxidant activity in polar aqueous medium inside the cells, using different experimental methods and theoretical quantum calculations. Data demonstrated the higher antioxidant capacity of DIP against ROS and free radicals in polar cell's interior. DIP is capable of generating long living and noninvasive DIP^• radicals in oxidant condition that leads to an effective “chain-breaking antioxidant” activity. Quantum computational data indicated that DIP antioxidant has more favorable ionization potential than trolox which means DIP has higher antioxidant activity. Also, data showed that the direct hydrogen-transfer is not a favorable process to construct DIP^• because of high barrier energy, though electron-transfer process can more easily to produce DIP^•+ with the lowest barrier energy. Altogether, the electron donating potency of DIP to reduce ferric ion, having the low anodic oxidation peak potential, producing long lived stable DIP^• radicals and protecting myoblast cells from oxidation, proposed the excellent “chain-breaking antioxidant” potency via electron-transfer mechanism of this vasodilator DIP drug in polar aqueous medium.

Electron paramagnetic resonance study of lipid and protein membrane components of erythrocytes oxidized with hydrogen peroxide

Electron paramagnetic resonance (EPR) spectroscopy of spin labels was used to monitor membrane dynamic changes in erythrocytes subjected to oxidative stress with hydrogen peroxide (H(2)O(2)). The lipid spin label, 5-doxyl stearic acid, responded to dramatic reductions in membrane fluidity, which was correlated with increases in the protein content of the membrane. Membrane rigidity, associated with the binding of hemoglobin (Hb) to the erythrocyte membrane, was also indicated by a spin-labeled maleimide, 5-MSL, covalently bound to the sulfhydryl groups of membrane proteins. At 2% hematocrit, these alterations in membrane occurred at very low concentrations of H(2)O(2) (50 µM) after only 5 min of incubation at 37°C in azide phosphate buffer, pH 7.4. Lipid peroxidation, suggested by oxidative hemolysis and malondialdehyde formation, started at 300 µM H(2)O(2) (for incubation of 3 h), which is a concentration about six times higher than those detected with the probes. Ascorbic acid and α-tocopherol protected the membrane against lipoperoxidation, but did not prevent the binding of proteins to the erythrocyte membrane. Moreover, the antioxidant (+)-catechin, which also failed to prevent the cross-linking of cytoskeletal proteins with Hb, was very effective in protecting erythrocyte ghosts from lipid peroxidation induced by the Fenton reaction. This study also showed that EPR spectroscopy can be useful to assess the molecular dynamics of red blood cell membranes in both the lipid and protein domains and examine oxidation processes in a system that is so vulnerable to oxidation.

Characterization, lung targeting profile and therapeutic efficiency of dipyridamole liposomes

The acute respiratory distress syndrome (ARDS) is a severe form of acute lung injury (ALI). Its pathogenesis is closely linked with reactive oxygen species (ROS). Antioxidation has been considered as an efficient treatment. Besides, liposomes are widely investigated as potential drug carriers due to their ability to protect and carry drug molecules to the target organ such as the lung. The present study was undertaken to investigate whether dipyridamole (DIP), delivered as a liposomal preparation, can ameliorate the lipopolysaccharides (LPS)-induced ALI due to the changes of its biodistribution. First, the liposomes entrapping DIP were prepared by film hydration for treating ARDS. Subsequently, the characterizations including entrapment efficiency, size, span and micrograph of DIP liposomes were measured. The concentration change of DIP in tissues and plasma of mice after intravenous administration of DIP injection and DIP liposomes was determined by RP-HPLC and calculated to lung targeting parameters. To prove the therapeutic efficiency, the effects of DIP liposomes on LPS-induced ALI were studied compared with DIP injection. The results showed DIP liposomes have the relative high entrapment efficiency and satisfying particle size. Compared with DIP injection, the liposomes increased the accumulation of DIP in the lung on a vast scale. Furthermore, DIP liposomes alleviated the ALI induced by LPS significantly. All of the results suggested that DIP liposomes have the potential efficacy in treating ALI/ARDS due to their obvious lung targeting.

Different oxidized phospholipid molecules unequally affect bilayer packing

The aim of this study was to gain more detailed knowledge about the effect of the presence of defined oxidized phospholipid molecules in phospholipid bilayers. After chromatographic and mass spectrometry analysis, the previously used product of the Fenton reaction with unsaturated lecithins proved to consist of a plethora of oxidatively modified lecithins, useless either for the detailed study of the effects brought about in the bilayer or as the source of defined oxidized phospholipid molecules. The latter, particularly 2-(omega-carboxyacyl)- and 2-(n-hydroperoxyacyl)-lecithins, can be more conveniently prepared by chemical or enzymatic synthesis rather than by chemical or physical oxidation. The effect of those molecules and of commercially available 12-hydroxy-stearic and dodecanedioic acid was studied in planar supported phospholipid bilayers (SPBs) by use of EPR spectrometry. The SPBs also contained 2-(5-doxylstearoyl)-lecithin as the spin probe, and the EPR spectral anisotropy loss, indicative of bilayer disordering, was measured as a function of the molar percentage of oxidized lipid. Most oxidized lipid molecules examined in this study were able to induce bilayer disordering, while hydroperoxyl group-bearing acyl chains appeared to be much less effective. It is concluded that the effects of different oxidized phospholipids on phospholipid bilayer structure cannot be generalized, as happens with batch-oxidized phospholipids, and that the use of defined oxidized phospholipid molecular species for membrane oxidative stress guarantees a more reliable and detailed response.

Combination treatment with dipyridamole, aspirin, and tPA in an embolic model of stroke in rats

Antithrombotic therapy has been shown to be effective in preventing secondary strokes. Inhibition of platelet function may reduce formation of thrombi thereby reducing the incidence of stroke. However, stronger inhibition of platelets is correlated with increased risk of bleeding events. The purpose of this study was to test the protective effects of combination therapy with dipyridamole and acetylsalicylic acid (ASA) in comparison to ASA alone, and whether such combination treatment may produce any added benefits when tissue plasminogen activator (tPA) treatment is also used. The study was divided into three parts. In part A, effect of antiplatelets on infarct volume was assessed. In part B, perfusion deficits were measured. In part C, efficacy of antiplatelet therapy in combination with tPA was assessed. In part A, dipyridamole and aspirin treatment significantly reduced infarct volume (P<0.05). In part B, treatment with dipyridamole significantly reduced the perfusion deficits as compared to control (P<0.05). In part C, dipyridamole plus tPA or dipyridamole and aspirin plus tPA significantly decreased infarct volume as compared to tPA alone (P<0.05). The present study suggests that there is significant protection with dipyridamole as both infarct volume and perfusion deficits are significantly reduced. Dipyridamole with tPA also significantly reduced infarct volume as compared to tPA alone. Our data suggests that higher doses of antithrombotic therapy with dipyridamole offer best neuroprotection.

Semiempirical quantum mechanical calculations of dipolar interaction between dipyridamole and dipalmitoyl phosphatidyl choline in Langmuir monolayers

Recent studies have shown that dipalmitoyl phosphatidyl choline (DPPC) monolayers respond cooperatively to the presence of dipyridamole (DIP) guest molecules even at small concentrations, which is a signature of molecular recognition. Using semiempirical quantum mechanical calculations for the DIP-DPPC system, we show that the incorporation of DIP causes large changes in the vertical dipole moment of the DIP-DPPC system, which can explain why measurable changes in surface potential are observed experimentally even at very low DIP concentrations. The calculations are also consistent with the anomalous concentration dependence of the surface pressure and surface potential isotherms for DIP-DPPC monolayers. Rather than saturation or a continuous increase in the effects caused by the incorporation of increasing amounts of DIP, the experimentally observed inversion in the behavior of the surface potential as the DIP concentration reaches 0.5 mol % would be caused by a change in DIP conformation, from a vertical arrangement for the DIP rings to a horizontal or intermediate arrangement. The strong dipolar interactions indicated in the calculations may also be the origin of the drastic changes in monolayer morphology seen in fluorescence microscopy images, with triskellion-shaped domains being formed for condensed DIP-DPPC monolayers.

Characterization of two oxidatively modified phospholipids in mixed monolayers with DPPC

The properties of two oxidatively modified phospholipids viz. 1-palmitoyl-2-(9'-oxo-nonanoyl)-sn-glycero-3-phosphocholine (PoxnoPC) and 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazePC), were investigated using a Langmuir balance, recording force-area (pi-A) isotherms and surface potential psi. In mixed monolayers with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) a progressive disappearance of the liquid expanded-liquid condensed transition and film expansion was observed with increasing content of the oxidized phospholipids. The above is in agreement with fluorescence microscopy of the monolayers, which revealed an increase in the liquid expanded region of DPPC monolayers. At a critical pressure pi(s) approximately 42 mN/m both Poxo- and PazePC induced a deflection in the pi-A isotherms, which could be rationalized in terms of reorientation of the oxidatively modified acyl chains into aqueous phase (adaptation of the so-called extended conformation), followed upon further film compression by solubilization of the oxidized phospholipids into the aqueous phase. Surface potential displayed a discontinuity at the same value of area/molecule, corresponding to the loss of the oxidized phospholipids from the monolayers. Our data support the view that lipid oxidation modifies both the small-scale structural dynamics of biological membranes as well as their more macroscopic lateral organization. Accordingly, oxidatively modified lipids can be expected to influence the organization and functions of membrane associated proteins.

Enzymatic oxidation of dipyridamole in homogeneous and micellar solutions in the horseradish peroxidase–hydrogen peroxide system

Enzymatic oxidation of dipyridamole (DIP) by horseradish peroxidase-hydrogen peroxide system (HRP-H2O2) in aqueous and micellar solutions was carried out. The reaction was monitored by optical absorption and fluorescence techniques. In aqueous solution at pH 7.0 and pH 9.0, the disappearance of the characteristic bands of DIP centered at 400 nm and 280 nm was observed. A new strong band at 260 nm is observed for the oxidation product(s) with shoulders at 322 nm and 390 nm. A non-fluorescent product is formed upon oxidation. In cationic cethyl trimethyl-1-ammonium chloride (CTAC) and zwitterionic 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS) micellar solutions the same results are observed: three, well-defined, isosbestic points in the optical spectra suggest the transformation between two species. In anionic micellar sodium dodecylsulfate solution (SDS), the appearance of a new band centered around 506 nm was observed, associated to a solution color change from the usual yellow to deep blue/violet, characteristic of a radical species associated to the one-electron oxidation of DIP to its cation radical (DIP*+), observed previously in electrochemical oxidation. Experiments of radical decay kinetics monitoring the absorbance change at 506 nm were performed and analyzed in the frame of a kinetic model taking into account the species both in homogeneous and micellar media. The reaction medium is composed of bulk solution, SDS micelle/solution interface and enzyme catalytic site(s). The variation of DIP*+ concentration was analyzed assuming: (1) synthesis of DIP*+ by HRP through one-electron oxidation; (2) decomposition of DIP*+ by further one-electron oxidation; (3) direct two-electron oxidation of DIP by HRP; (4) bimolecular DIP*+ disproportionation. The main results of the analysis are as follows: (1) kinetic data can be divided in two phases, an HRP active phase and another phase which proceeds in the absence of enzyme activity due to consumption of all H2O2; (2) the reactions of DIP*+ formation, DIP*+ decomposition and DIP two-electron oxidation are HRP concentration dependent; (3) since DIP*+ formation constant seems to be overestimated, it is proposed that two-electron oxidation is another source of DIP*+, through the comproportionation reaction. Evidences for this reaction were also observed previously in electrochemical experiments; and (4) the kinetic analysis provides evidences that the bimolecular reaction of DIP*+ takes place mainly in the absence of active HRP and in this phase the combination of, at least, two second-order kinetic processes is needed to model the experimental data. Our data suggest that HRP oxidizes DIP in general by a two-electron process or that the cation radical is very unstable so that the one-electron process is only detected in the presence of anionic surfactant, which stabilizes significantly the DIP*+ intermediate.

Oxidized phospholipids induce phase separation in lipid vesicles

The thermal behaviour of phospholipid multilamellar vesicles (MLV) made of various molar percentages of DPPC and LPPC, containing also oxidized LPPC (LPPCox), was studied by use of EPR spectroscopy and n-DSPC spin label in order to determine variations in the membrane fluidity brought about by lipid oxidation. Experimental variables were temperature, ranging from 4 to 44 degrees C, and molar percentage composition of DPPC/LPPC/LPPCox ternary mixture. We found that the presence of LPPCox in a percentage higher than both normal phospholipids' heavily hindered membrane formation, while lower percentage of the oxidized lipid with higher DPPC percentages yielded two-components EPR spectra, showing the presence of two different fluidity domains, indicative of membrane phase separation. When LPPC was the dominant lipid in the ternary mixture, simple EPR spectra were observed, indicating homogeneity of MLV membranes. Phase separation observed in the presence of LPPCox was better visible at lower temperature (12 degrees C or less), and almost disappeared with increasing temperature (36 degrees C or more). Furthermore, the correlation time of 16-DSPC in ternary mixture MLVs with higher LPPC percentage (homogeneous membranes) was not affected by the presence of LPPCox, while it normally increased upon DPPC percentage increase, as readily calculated from the EPR spectra featuring simple bands at 24 degrees C. It is concluded that oxidized lipid induces phase separation in more rigid DPPC-rich membranes, while leaving fluidity unaffected in more fluid LPPC-rich membranes, and at higher temperature.

Leakage of Potassium from Red Blood Cells following Gamma Ray Irradiation in the Presence of Dipyridamole, Trolox, Human Plasma or Mannitol

Transfusion-associated graft-versus-host disease (TA-GVHD) is a fatal complication of blood transfusion resulting from the contamination of blood products by leukocytes. In order to prevent this disease, gamma or X-ray irradiation of blood components,which can inactivate leukocytes, is currently used. However, the minimal doses needed to destroy lymphocytes promote the leakage of potassium from red blood cells (RBCs), which can induce other side effects, such as hyperpotassemia and cardiac arrest. The reactive oxygen species (ROS) generated by the irradiation of aqueous solutions may accelerate the leakage through oxidation of the RBC membrane. Here we studied the effect of dipyridamole, Trolox, human plasma or mannitol on the leakage of potassium from RBCs following irradiation. RBC preparations (hematocrit; 30%) containing antioxidants were irradiated at 30 Gy and stored at 4 degrees C for 7 d. The leakage of potassium from the RBCs caused by the irradiation was significantly suppressed by dipyridamole (more than 50 microM), Trolox (more than 5 mM) or human plasma (50%). Mannitol (80 mM) is used to inhibit hemolysis as a constituent of MAP solution, which is a solution used for the storage of RBC products in Japan. Here it was clarified that the leakage of potassium from not only irradiated but also non-irradiated RBCs was unexpectedly promoted by mannitol. The amount of mannitol in MAP solution may have to be reconsidered. The osmotic pressure of the RBC preparation increased in a manner dependent on the concentration of mannitol. The elevated osmotic pressure may promote the leakage. In conclusion, although antioxidants have the potential to suppress the leakage of potassium ascribed to the irradiation, the extent of the suppression (10-20%) by dipyridamole (DPM), Trolox or human plasma seems insufficient for the clinical use of these agents as an additive for MAP solution.

Dipyridamole increases the cytotoxicity of cisplatin in human larynx cancer cells in vitro

This paper describes the effect of dipyridamole (DIP) on the cytotoxicity of cisplatin in HEp-2 human larynx cancer cells in vitro and the nature of the interaction between cisplatin and dipyridamole. Cytotoxic assays were performed to obtain the IC50 for cisplatin. The cells were treated with 0, 20, 40, 80, 120 or 200 microM cisplatin, with or without a single concentration of DIP and incubated for 60 min at 37 masculine C and 5% CO2 for 3 days and then counted with a hemocytometer. The accumulation of cisplatin in the cells was measured by atomic absorption and fluorescence was used to determine the membrane binding constant of DIP. In the presence of 10, 20 and 30 microM DIP, the IC50 of cisplatin was reduced by 25, 60 and 82% in HEp-2 cells. Combination index analysis revealed that cisplatin and DIP interact synergistically. In larynx cancer cells, the accumulation of cisplatin increased by 13, 27 and 65% as the DIP concentration was increased from 10 to 20 and 30 microM, respectively. The binding constant of DIP to the cell membrane was estimated to be 0.36 +/- 0.12 mg/ml(-1) (N = 2) by fluorescence and cisplatin did not suppress DIP fluorescence. These results suggest that DIP significantly enhances cisplatin cytotoxicity in HEp-2 cells by increasing cisplatin accumulation, probably by altering the cell membrane as suggested by its binding constant. The results obtained reinforce the importance of combination therapy to reduce the doses of chemotherapeutic drugs and therefore the side effects of chemotherapy.

EPR studies of phospholipid bilayers after lipoperoxidation

The molecular order of fatty acyl chains in oriented lipid bilayers on solid support (SPB), made of either natural or synthetic phospholipids oxidized by Fenton reagent and probed with spin labeled lecithin (5-DSPC) was studied by means of EPR spectrometry. Phospholipids (ASPC, EYPC, mitochondrial extract) were oxidized as either aqueous buffer/methanol dispersions or reverse-phase evaporation vesicles (REV) suspensions. Oxidation was preliminarily revealed both by assaying MDA and by detecting conjugated dienes. Oxidized phospholipid species was quantified by preparative TLC. The degree of order in oriented lipid bilayers of samples containing oxidized phospholipids was estimated by the loss of EPR spectral anisotropy, and an empirical index of the related bilayer disorder was calculated from the second derivative spectra. Bilayers made of each non-oxidized phospholipid species from either ethanol solutions or REV suspensions showed the highest anisotropy, while the increasing presence of oxidized lipids in the samples resulted in progressive loss of EPR spectral anisotropy. In contrast, vesicles containing 40% of the oxidized species maintained an unaltered fluidity gradient, while REV formation was hindered by oxidized phospholipid percentages higher than 45% for ASPC and EYPC, and 35% for Mitochondrial lipids (MtL). It is concluded that the early stages of lipoperoxidation bring about disordering of the phospholipid bilayer interior rather than fluidity alterations, and that prolonged oxidation may result in loss of structural and chemical properties of the bilayer until the structure no longer holds.

Respiration state IV-generated ROS destroy the mitochondrial bilayer packing order in vitro. An EPR study

The aim of the present study was to detect defective structural properties in bilayers of mitochondrial phospholipids after oxidative stress of isolated mitochondria in vitro, reportedly during respiration state IV. The structural behaviour of extracted phospholipids was studied by electron paramagnetic resonance (EPR) spectrometry in oriented phospholipid bilayers spin-labelled with 5-doxyl-lecithin, by detecting of the degree of EPR spectral anisotropy loss, indicative of the phospholipid bilayer packing order. Bilayers of phospholipids from untreated mitochondria showed the highest spectral anisotropy, hence highly ordered structure, while chemically oxidised phospholipid yielded almost completely disordered supported phospholipid bilayers. Samples from mitochondria after respiration state IV showed bilayer disorder increasing with oxidation time, while inclusion of the antioxidant resveratrol in the respiration medium almost completely prevented bilayer disordering. On the other hand, beta-n-doxylstearoyl-lecithin spin-labelled mitochondria showed unchanged order parameter S at C positions 5, 12 and 16 after respiration state IV, confirming the insensitivity of this parameter to phospholipid oxidative stress. It is concluded that reactive oxygen species attack to the membrane affects lipid packing order more than fluidity, and that EPR anisotropy loss reveals oxidative damage to the bilayer better than the order parameter.

Fragmentation of dipyridamole and related dipyrimidines by electrospray ionization collisional activated decomposition mass spectrometry

The coronary vasodilator, co-activator of antitumor compounds and antioxidant drug dipyridamole and several of its derivatives were studied by electrospray ionization (ESI) combined with collisional activated decomposition (CAD) in both positive and negative modes. These compounds produce abundant monocharged ions ([M + H](+)) under ESI. Interpretation of the CAD spectra showed that fragmentation occurs preferentially in the ethanolamine groups attached at C-2, C-4, C-6 and C-8. 2-Methoxyethanol is eliminated when ethanolamines are in positions C-2/C-6 and 2-aziridinethanol is eliminated from C-4/C-8 ethanolamines. The proposed fragmentation schemes were supported by deuterium labeling experiments and tandem mass spectrometry.

Opposite effects of Mn(III) and Fe(III) forms of meso-tetrakis(4-N-methyl pyridiniumyl) porphyrins on isolated rat liver mitochondria

The relevance of porphyrins as therapeutic drugs targeted to mitochondria has been widely recognized. In this work, we studied the action of meso-tetrakis porphyrins (TMPyP) on respiring rat liver mitochondria. Mn(III)TMPyP exerted a protective effect against lipid peroxidation induced by Fe(II) or the azo initiator 4,4'-azobis(4-cyanopentanoic acid) (ABCPA), which partition in the hydrophobic phospholipid moiety, and 2,2'-azobis(2-amidinepropane)dihydrochloride (ABAP), which partitions in the aqueous phase. In contrast, Fe(III)TMPyP itself induced an intense lipid peroxidation, accompanied by mitochondrial permeability transition. Both mesoporphyrins studied promoted a release of mitochondrial state-4 respiration, in the concentration range of 1.0-20 microM. Based on the relative effects of Mn(III)TMPyP against ABAP and ABCPA-induced lipid peroxidation, we believe that meso-tetrakis porphyrins must concentrate preferably at membrane-water interfaces.

In vitro antioxidant and photo-oxidant properties of dipyridamole

The in vitro antioxidant and photo-oxidant activity of dipyridamole was studied by its effect on superoxide- and singlet oxygen-mediated photohemolysis and viability of neutrophils. Dipyridamole was found to be phototoxic when examined by the photohemolysis on human erythrocytes and on linoleic acid as lipid peroxidation model at concentrations above 3.0 x 10(-5) M. On the contrary, when lower concentrations (1.0 x 10(-5) to 1.0 x 10(-6) M) were used, dipyridamole showed a protector action against singlet oxygen-mediated photohemolysis by other phototoxic compounds like triamterene. This antioxidant property is proposed to result from quenching of triamterene mediated by fluorescence energy transfer. Auto-oxidation and fluorescence-energy transfer is clearly an important mechanism for protection for this drug.

Cooperativity of phospholipid reorganization upon interaction of dipyridamole with surface monolayers on water

Results from various surface sensitive characterization techniques suggest a model for the interaction of the piperidinopyrimidine dipyridamole (DIP)--known as a vasodilator and inhibitor of P-glycoprotein associated multidrug resistance of tumor cells--with phospholipid monolayers in which the drug is peripherally associated with the membrane, binding (up to) five phospholipids at a time. These multiple interactions are responsible for a very strong association of the drug with the lipid monolayer even at exceedingly low concentrations (approximately 0.2 mol%). Electrostatic interactions and hydrogen bonding are likely involved in the binding of DIP to DPPC. Cooperative effects among the lipids are invoked to explain the macroscopically measurable changes of lipid monolayer properties even when only one out of 100 DPPC molecules is directly associated with a DIP molecule. A reversal of the observed changes upon drug association with the membrane as the DIP concentration surpasses a threshold concentration (c(crit)approximately 0.5 mol%) may be explained by cooperativity in a different context, the self-aggregation of drug molecules. With its implications for the interaction of DIP with phospholipid films, this work provides a first approach to the explanation of the high sensitivity of cell membranes to piperidinopyrimidine drugs on a molecular level.

Selective protection of RBCs against photodynamic damage by the band 3 ligand dipyridamole

BACKGROUND

All studied photosensitizers for virus inactivation impair RBCs. To reduce damage to the RBCs without affecting virucidal activity, selective protection of the RBCs is necessary. The ability of the band 3 ligand, dipyridamole, to react with singlet oxygen and to increase the selectivity of photosterilization was investigated.

STUDY DESIGN AND METHODS

Solutions of dipyridamole were illuminated in the presence of tetrasulfonated aluminum phthalocyanine (AlPcS(4)) and dimethylmethylene blue (DMMB). Solutions of amino acids, RBCs, and vesicular stomatitis virus (VSV) in RBC suspensions were photodynamically treated in the presence or absence of dipyridamole.

RESULTS

Illumination of a solution of dipyridamole in the presence of AlPcS(4) or DMMB resulted in changes in the optical spectrum of dipyridamole. The photooxidation of dipyridamole was inhibited by azide and augmented by D(2)O, which suggests the involvement of singlet oxygen. Photooxidation of amino acids and photodamage to RBCs was strongly reduced in the presence of dipyridamole. In contrast, photoinactivation of VSV in RBC suspensions was only slightly affected by dipyridamole.

CONCLUSION

Dipyridamole can improve the specificity of photodynamic sterilization of RBC concentrates, thereby increasing the practical applicability of this photodecontamination method.

Dipyridamole and its derivatives modify the kinetics of the electron transport in reaction centers from Rhodobacter sphaeroides

A well known vasodilator dipyridamole (DIP), 2,6-bis(diethanolamino)-4,8-dipiperidinopyrimido[5,4-d]pyrim idine, and its derivatives have recently been shown as potential co-activators (modulators) in the phenomenon of multidrug resistance (MDR) in cancer therapy. They inhibit the specific function of a transmembrane P-glycoprotein responsible for the ex-flux of anti-cancer drugs from tumor cells. To clarify molecular mechanisms of the anti-MDR activity of DIP and its two derivatives, RA25 and RA47, we have studied their effects on electron transport in reaction centers (RC) from purple photosynthetic bacteria Rb. sphaeroides, using RC as a model system. Increasing concentrations of DIP and RA47 progressively accelerate the back electron transfer from the primary quinone acceptor QA to the bacteriochlorophyll dimer Bchl2 (Bchl2+ -QA- recombination). In the absence of o-phenantroline, when both quinone acceptors QA and QB are involved in the electron transport, RA47 is more effective than DIP. DIP stabilizes the electron on the secondary quinone acceptor QB, the effect manifested as the retardation of Bchl2+ -QB- recombination. Effects of RA25 are negligible in all cases. The drugs are proposed to change the electron transport affecting the RC structural dynamics and the stabilization of the electron on quinone acceptors through modification of H-bonds in the system.

Antioxidant effect of dipyridamole and its derivative RA-25 in mitochondria: correlation of activity and location in the membrane

Dipyridamole (DIP), a coronary vasodilator, presents coactivator activity for a number of antitumor drugs as well as antioxidant activity in membrane systems. DIP and derivatives interact with membrane systems such as micelles, phospholipid monolayers and vesicles. The antioxidant effect of DIP and several derivatives upon iron-induced lipoperoxidation on mitochondria has been reported and a good correlation between the hydrophobicity and their protective effect was found (M.F. Nepomuceno et al., Free Radic. Biol. Med., 23 (1997) 1046-1054). In the present work an effort is made to better understand the role of DIP as inhibitor of Fe2+-induced lipid peroxidation in mitochondria. At low concentration, no significant effect on either state IV or state III respiration was found, discarding a possible direct interaction of DIP or RA-25 with the peripheral benzodiazepine receptor. The association constants for DIP and RA-25 in mitochondria were estimated, being 0.7 (mg/ml)-1 for DIP and 0.2 (mg/ml)-1 for RA-25. Oxygen consumption studies in the presence of FeSO4 showed that the antioxidant effect of DIP or RA-25 did not involved the initial step of Fe2+ oxidation. Our data strongly support the hypothesis that the antioxidant effect of both DIP and RA-25 is related to their partition in the lipid phase of the mitochondrial membrane and not to a specific interaction with membrane proteins. This protection may be due either to a direct inhibition of the propagation steps or a scavenger effect on the radicular species that would trigger the peroxidative process.

Different Micellar Packing and Hydrophobicity of the Membrane Probes TEMPO and TEMPOL Influence Their Partition Between Aqueous and Micellar Phases Rather than Location in the Micelle Interior

We report the investigation of the distribution of two stable nitroxyl radicals, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and 4-hydroxy-TEMPO (TEMPOL), between aqueous and micellar phases and in the micelle interior by quenching of fluorescence of dipyridamole (DIP) and by 1H NMR, ESR, and optical absorption spectroscopies. Cationic cetyltrimethylammonium chloride (CTAC), anionic sodium dodecylsulfate (SDS), zwitterionic N-hexadecyl-N,N-dimethyl 3-ammonio-1-propanesulfonate (HPS), and non-ionic octylphenoxypolyethoxyethanol (Triton X-l00) micelles were used. In all types of micelles the binding constants for more hydrophobic TEMPO appear higher than those for TEMPOL. At the same time the 1H NMR and optical absorption data show that the distribution of both radicals in the micelle interior is practically the same: The paramagnetic fragments are localized in the interface between the polar headgroup region and the hydrophobic interior of micelles. There is no clear correlation between Kb and the micelle charge. Indeed, Kb for TEMPO with SDS (2150 M-1) is lower than with CTAC (3250 M-1), but higher than with Triton X-l00 (1300 M-1) or HPS (1000 M-1). The Kb values correlate quite well with the packing of the monomers in the micelle, being higher for the loosely packed micelles (higher cmc). Besides, the micelle headgroup hydration water seems to decrease the binding constant. Copyright 1998 Academic Press.