Medium effects on the antioxidant activity of dipyridamole

Nitroxides as Building Blocks for Nanoantioxidants

Nitroxides are an important class of radical trapping antioxidants whose promising biological activities are connected to their ability to scavenge peroxyl (ROO^•) radicals. We have measured the rate constants of the reaction with ROO^• (k_inh) for a series of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) derivatives as 5.1 × 10⁶, 1.1 × 10⁶, 5.4 × 10⁵, 3.7 × 10⁵, 1.1 × 10⁵, 1.9 × 10⁵, and 5.6 × 10⁴ M^-1 s^-1 for -H, -OH, -NH₂, -COOH, -NHCOCH₃, -CONH(CH₂)₃CH₃, and ═O substituents in the 4 position, with a good Marcus relationship between log (k_inh) and E° for the R₂NO^•/R₂NO⁺ couple. Newly synthesized Pluronic-silica nanoparticles (PluS) having nitroxide moieties covalently bound to the silica surface (PluS-NO) through a TEMPO-CONH-R link and coumarin dyes embedded in the silica core, has k_inh = 1.5 × 10⁵ M^-1 s^-1. Each PluS-bound nitroxide displays an inhibition duration nearly double that of a structurally related "free" nitroxide. As each PluS-NO particle bears an average of 30 nitroxide units, this yields an overall ≈60-fold larger inhibition of the PluS-NO nanoantioxidant compared to the molecular analogue. The implications of these results for the development of novel nanoantioxidants based on nitroxide derivatives are discussed, such as the choice of the best linkage group and the importance of the regeneration cycle in determining the duration of inhibition.

Dipyridamole-induced C-type natriuretic peptide mRNA overexpression in a minipig model of pacing-induced left ventricular dysfunction

Dipyridamole (DP) restores ischemic tissue blood flow stimulating angiogenesis in eNOS-dependent pathways. C-type natriuretic peptide (CNP) is expected to mimic the migration-stimulatory effect of NO via a cGMP-dependent mechanism. Aim of this study was to assess the role of concomitant treatment with DP on CNP levels in blood and myocardial tissue of minipigs with left ventricular dysfunction (LVD) induced by pacing at 200bpm in the right ventricular apex. Minipigs with DP therapy (DP+, n=4) or placebo (DP-, n=4) and controls (C-SHAM, n=4) underwent 2D-EchoDoppler examination and blood collection before and after 4 weeks of pacing, when cardiac tissue was collected. Histological/immunohistochemical analyses were performed. CNP levels were determined by radioimmunoassay; cardiac CNP, BNP, natriuretic receptors expression by Real-Time PCR. After pacing, cardiac parameters resulted less impaired in DP+ compared to DP-. Histological sections presented normal morphology while the arteriolar density resulted: C-SHAM: 9.0±1.2; DP-: 4.9±0.3; DP+: 6.5±0.6number/mm(2); C-SHAM vs DP- and DP+ p=0.004, p=0.04, respectively. CNP mRNA resulted lower in DP- compared to C-SHAM and DP+ as well as NPR-B (p=0.011, DP- vs DP+). Both NPR-A/NPR-C mRNA expressions were significantly (p<0.001) lower both in DP- and DP+ compared to C-SHAM. BNP mRNA was higher in LVD. CNP plasma levels showed a similar trend with respect to gene expression (C-SHAM: 30.5±15; DP-: 18.6±5.5; DP+: 21.2±4.7pg/ml). These data suggest that DP may serve as a preconditioning agent to increase the protective CNP-mediated endocrine response in LVD. This response, mediated by its specific receptor NPR-B, may offer new insights into molecular targets for treatment of LVD.

Dietary phenolic acids act as effective antioxidants in membrane models and in cultured cells, exhibiting proapoptotic effects in leukaemia cells

Caffeic, syringic, and protocatechuic acids are phenolic acids derived directly from food intake or come from the gut metabolism of polyphenols. In this study, the antioxidant activity of these compounds was at first evaluated in membrane models, where caffeic acid behaved as a very effective chain-breaking antioxidant, whereas syringic and protocatechuic acids were only retardants of lipid peroxidation. However, all three compounds acted as good scavengers of reactive species in cultured cells subjected to exogenous oxidative stress produced by low level of H(2)O(2). Many tumour cells are characterised by increased ROS levels compared with their noncancerous counterparts. Therefore, we investigated whether phenolic acids, at low concentrations, comparable to those present in human plasma, were able to decrease basal reactive species. Results show that phenolic acids reduced ROS in a leukaemia cell line (HEL), whereas no effect was observed in normal cells, such as HUVEC. The compounds exhibited no toxicity to normal cells while they decreased proliferation in leukaemia cells, inducing apoptosis. In the debate on optimal ROS-manipulating strategies in cancer therapy, our work in leukaemia cells supports the antioxidant ROS-depleting approach.

Endothelial dysfunction and diabetes: effects on angiogenesis, vascular remodeling, and wound healing

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by inappropriate hyperglycemia due to lack of or resistance to insulin. Patients with DM are frequently afflicted with ischemic vascular disease or wound healing defect. It is well known that type 2 DM causes amplification of the atherosclerotic process, endothelial cell dysfunction, glycosylation of extracellular matrix proteins, and vascular denervation. These complications ultimately lead to impairment of neovascularization and diabetic wound healing. Therapeutic angiogenesis remains an attractive treatment modality for chronic ischemic disorders including PAD and/or diabetic wound healing. Many experimental studies have identified better approaches for diabetic cardiovascular complications, however, successful clinical translation has been limited possibly due to the narrow therapeutic targets of these agents or the lack of rigorous evaluation of pathology and therapeutic mechanisms in experimental models of disease. This paper discusses the current body of evidence identifying endothelial dysfunction and impaired angiogenesis during diabetes.

Dipyridamole reverses peripheral ischemia and induces angiogenesis in the Db/Db diabetic mouse hind-limb model by decreasing oxidative stress

Dipyridamole anti-platelet therapy has previously been suggested to ameliorate chronic tissue ischemia in healthy animals. However, it is not known if dipyridamole therapy represents a viable approach to alleviating chronic peripheral tissue ischemia associated with type 2 diabetes. Here we examine the hypothesis that dipyridamole treatment restores reperfusion of chronic hind-limb ischemia in the murine B6.BKS-Lepr(db/db) diabetic model. Dipyridamole therapy quickly rectified ischemic hind-limb blood flow to near preligation levels within 3 days of the start of therapy. Restoration of ischemic tissue blood flow was associated with increased vascular density and endothelial cell proliferation observed only in ischemic limbs. Dipyridamole significantly increased total nitric oxide metabolite levels in tissue, which were not associated with changes in endothelial NO synthase expression or phosphorylation. Interestingly, dipyridamole therapy significantly decreased ischemic tissue superoxide and protein carbonyl levels, identifying a dominant antioxidant mechanistic response. Dipyridamole therapy also moderately reduced diabetic hyperglycemia and attenuated development of dyslipidemia over time. Together, these data reveal that dipyridamole therapy is an effective modality for the treatment of chronic tissue ischemia during diabetes and highlights the importance of dipyridamole antioxidant activity in restoring tissue NO bioavailability during diabetes.

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.

Biomedical modification of poly(L-lactide) by blending with lecithin

Lecithin was, for the first time, blended with PLLA to prepare scaffold material for tissue engineering applications in the present study. Solution blending was used to incorporate Lecithin (containing 0-10 wt %) with PLLA to enhance the blend films biocompatibility, hydrophilicity and toughness while maintaining mechanical strength of PLLA. The results of FTIR-ATR analysis indicated that the amino groups of lecitin existed in the films. DSC analysis indicated that T(g) decreased with the increase of lecithin content in the blend films. The percentage elongation markedly increased with increase of lecithin content. The proliferation and viability of the vascular smooth muscle cell cultures on PLLA/Lecithin (containing 3-7 wt %) films were significantly enhanced compared to pure PLLA on tissue culture plates.

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.

Dipyridamole is neuroprotective for cultured rat embryonic cortical neurons

The effects of a clinically useful cardiovascular agent, dipyridamole, were examined in a rodent tissue culture model of neuroprotection. Dipyridamole effectively protected rat embryonic day 18 (E18) cortical neurons from either 48 h trophic deprivation or 48 h exposure to the glutathione synthesis inhibitor, L-buthionine (R,S) sulfoximine. The neuron sparing actions of dipyridamole were time- and concentration-dependent and mimicked the actions of exogenously applied glutathione. These results demonstrate that dipyridamole protects primary neuronal cultures against either trophic or chemically mediated insults, and suggest that dipyridamole has a potent antioxidant ability that compensates for glutathione depletion in neuronal cultures.

Phenolic antioxidants: electrochemical behavior and the mechanistic elements underlying their anodic oxidation reaction

Electrochemical analysis has been widely used to assess activities of reductant antioxidants, but the mechanistic factors that determine reducing ability and their corresponding correlations remain to be explored further. In the present paper, the reactivity of a selection of phenolic compounds in anodic oxidation was investigated by cyclic voltammetry (CV). The effects of electron-donation ability, deprotonation equilibrium, stability of radicals and chemical hardness on reducing capacity were studied by computational chemistry methods and multiple linear regression analysis. The results suggested that all these factors made significant contributions to reducing potency although electron-donation ability of the parent molecule plays the most important role in the electrode reaction. With the majority of the compounds examined, the occurrence of multiple electrochemical reactions leading to irreversible anodic oxidation was implied by: (i) the characteristics of the radical cation intermediate; (ii) the propensity of the deprotonation reaction; and (iii) the reactivity of the parent molecule. Upon correlation analysis of oxidation potential and computed physicochemical descriptors, some new light was shed on the mechanism by which phenolic compounds act as antioxidant reductants in free radical reactions. A satisfactory multi-descriptor theoretical QSAR model was derived, which might be of predictive significance in the screening or design of new antioxidants.

Influence of dipyridamole on the fatty acid composition of the main lipid classes of chick serum

We have studied the effects of dipyridamole treatment on the fatty acid composition of the main lipid classes of chick serum bearing in mind the relationship between platelet aggregation and eicosanoids production from arachidonic acid. In the free fatty acids, percentages of MUFA and n-6 PUFA fell. The effects of dipyridamole appeared to be less pronounced in triglyceride fraction, but more so in serum phospholipids and cholesterol esters. The percentage of arachidonic acid was significantly reduced by dipyridamole, as well as that of different n-3 PUFA present in phospholipid fraction. The percentage of linoleic acid in serum cholesterol esters was significantly lowered by dipyridamole, whereas that of arachidonic acid did not change significantly. Our results suggest that decreased arachidonic acid in the serum phospholipids and linoleic acid in all lipid classes may be of importance in order to dipyridamole participation in several pathologies characterized by an imbalance in the production of vasodilator and vasoconstrictor prostanoids.

Antioxidant capacity of phenolic and related compounds: correlation among electrochemical, visible spectroscopy methods and structure-antioxidant activity

We investigated the antioxidant activity of phenylpropionic acids--caffeic (CAF), ferulic (FER), para-coumaric (COU) and cinnamic (CIN)--and phenolic acids and related compounds--gallic (GAL), methyl gallate (meGAL), vanillic (VAN) and gentisic (GEN)--using visible spectroscopy, inhibition of nitroblue tetrazolium (NBT) reduction, and electrochemical methods including cyclic voltammetry and potentiometry. In the spectroscopic assays, only CAF, GAL and meGAL were able to inhibit NBT reduction. The same compounds showed the lowest oxidation potentials (Epa) and the highest redox potentials deltaE) in the cyclic voltammetric and potentiometric studies, respectively. In addition, it was observed that the greater the number of hydroxyls linked to the aromatic ring, the greater was the antioxidant activity of the analysed compounds. The correlations of Spermann--used to compare the methods between themselves and the methods with the relationship structure-antioxidant activity--were r = -0.9762 for the cyclic voltammetric-potentiometric methods. r = 0.8333 for the inhibition of NBT reduction-potentiometric methods and r = -0.8095 for the inhibition of NBT reduction-cyclic voltammetric methods. The correlations for cyclic voltammetric, potentiometric and inhibition of NBT reduction methods-number of hydroxyls linked to the aromatic ring were r = -0.9636, 0.9636 and 0.9142, respectively. These findings indicate that the electrochemical methods together with spectroscopic studies are a good tool to evaluate the antioxidant activity of substances.

Dipyridamole prevents the coconut oil-induced hypercholesterolemia. A study on lipid plasma and lipoprotein composition

For a better understanding of the hypolipidemic function of dipyridamole, we have studied the comparative effects of diet supplementation with 10% coconut oil with and without dipyridamole on the lipid plasma and lipoprotein composition in chicks. This study was performed under postprandial and food-deprivation (12h) conditions. Coconut oil induced a clear hypercholesterolemia under both feeding conditions. Simultaneous administration of dipyridamole maintained total and esterified cholesterol at levels similar to those observed in control animals sacrificed under postprandial conditions. Under these conditions, our results also show that dipyridamole significantly reduced cholesterol levels in all the chick plasma lipoproteins that were increased by coconut oil administration. Nevertheless, it should be emphasised that the levels of total cholesterol found in intermediate- and very-low-density lipoproteins were lower than in control. All chemical components of these fractions were significantly decreased by dipyridamole. The effects were not significant in chicks deprived of food. In conclusion, our results show that the hypercholesterolemia induced by coconut oil was prevented by dipyridamole. To our knowledge, this is one of the first reports on the antihypercholesterolemic effects of dipyridamole.

Dipyridamole reduces cholesterol and triglyceride levels in plasma and lipoproteins from young chicks fed a saturated fat-enriched diet

We have studied the value of dipyridamole for the prevention of hypercholesterolemia caused by saturated fat. This study shows that supplementation of 10-20% coconut oil to the diet induced a significant hypercholesterolemia under postprandial conditions. Simultaneous administration of dipyridamole and 10% coconut oil for 2 weeks maintained plasma cholesterol and triglycerides at levels similar to control, counteracting the increase induced by coconut oil. Dipyridamole significantly reduced cholesterol levels in all the chick plasma lipoproteins that were increased by coconut oil administration. However, it should be emphasized that cholesterol and other chemical components were more drastically reduced by dipyridamole in intermediate- and very-low-density lipoproteins than in other lipoprotein fractions.

Antioxidant effect of oral dipyridamole during cerebral hypoperfusion with human carotid endarterectomy

We sought to test the hypothesis of an antioxidant effect of dipyridamole in vivo in a model of cerebral hypoperfusion. Twenty-one patients (65+/-10 years, 11 men) undergoing carotid endarterectomy were allocated in two groups (group 1, 10 with dipyridamole, 200 mg p.o., 3-4 h before surgery; group II, 11 with placebo) in a double-blind placebo-controlled randomized design. Blood was sampled from ipsilateral jugular bulb, and plasma vitamin E content was assayed before, after 15 and 30 min of clamp, and 2 and 10 min after declamping. In 12 of them, lipoperoxides were assayed. Vitamin E plasma content decreased significantly in group II (rest, 3.71+/-0.22 mmol/mol of cholesterol, 100%) after clamp (91.5% of rest, p < 0.01) and remained unchanged during declamping (90.9% of rest, p < 0.01), but did not change in group I (rest, 3.5+/-0.44 mmol/mol of cholesterol, 100%) during clamping (99.9% of rest; p = NS) and after declamping (97.6% of rest; p = NS). Lipoperoxide concentration did not change in group I (rest, 302+/-8 a.u.; clamp, 296+/-13 a.u.; p = NS vs. rest; declamp, 304+/-8 a.u.; p = NS vs. rest), and increased significantly in group II (rest, 313+/-5 a.u.; clamp, 352+/-9 a.u.; p < 0.01 vs. rest; declamp, 343+/-6 a.u.; p < 0.05 vs. rest). Cerebral oxidative stress associated with human carotid endarterectomy can be attenuated by pretreatment with oral dipyridamole.

Hypocholesterolemic activity of dipyridamole: effects on chick plasma and lipoprotein composition and arachidonic acid levels

We have studied the effects of dipyridamole treatment on chick plasma and lipoprotein composition in postprandial and fasting (12 h) conditions. Plasma cholesterol levels were higher in fasted than in fed chicks, whereas triglycerides declined during starvation. Dipyridamole treatment reduced plasma cholesterol content, mainly of the free cholesterol fraction. In postprandial conditions, total cholesterol content of high and low density lipoproteins decreased in a similar proportion to that observed in plasma. However, cholesterol and other chemical constituents of intermediate and very low density lipoproteins were more drastically reduced by dipyridamole than in plasma. Total amounts of these lipoprotein fractions were also reduced about 50%. The effects of dipyridamole in fasted animals were not significant. To our knowledge, this is one of the first reports about the response of lipoprotein cholesterol to dipyridamole treatment. A strong decrease was also found in the arachidonic acid content of plasma phospholipids and cholesterol esters fractions.