Dipyridamole and RA-642 inhibit the production of superoxide anion and free radical damage to rat lens

Ocular Applications of Dipyridamole: A Review of Indications and Routes of Administration

Dipyridamole was introduced decades ago as a treatment for angina, subsequently found to inhibit platelet aggregation. It is most commonly used, and approved for use in thromboembolism prevention, following surgery. Some of its recognized effects such as adenosine uptake inhibition, elevation of cAMP and cGMP levels, vasodilation, and tissue perfusion are important in various ocular disorders. For this reason, dipyridamole represents an interesting candidate as a therapeutic target for the treatment of eye disorders affecting different ocular structures. The aim of this article is to review the evidence and current understanding of the mechanisms by which dipyridamole exerts its effects on different ocular tissues, discuss the role of dipyridamole in clinical practice, and highlight areas of use and routes of administration.

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.

Effect of combination therapy with dipyridamole and quinapril in diabetic nephropathy

BACKGROUND/AIMS

Dipyridamole stimulates nitric oxide action via inhibition of phosphodiesterase and also has an antioxidant effect. ACE inhibitor reduces glomerular pressure and enhances NO action via increased bradykinin. Thus, we evaluated the effect of the combination of dipyridamole and ACE inhibitor in diabetic nephropathy.

METHODS

Streptozotocin-induced diabetic rats at 2 weeks were treated with dipyridamole, quinapril or both. The expression of NOS and NAD(P)H oxidase p47phox was investigated using immunohistochemistry and western blot, and urinary albumin, cGMP and lipid peroxidation products (LPO) were measured at 4 weeks.

RESULTS

NAD(P)H oxidase and urinary LPO were significantly enhanced in diabetes, and suppressed by each treatment to the same extent. The nNOS expression in macula densa and eNOS increased significantly with combination therapy compared to quinapril treatment alone contributing to an enhanced urinary excretion of cGMP and to maintain the creatinine clearance. Increased albuminuria in diabetes was reduced more effectively with combination therapy to the control level than with single treatments.

CONCLUSION

Combination therapy with dipyridamole and quinapril suppressed urinary LPO via reduction of NAD(P)H oxidase increase in diabetes. The combination therapy reduced microalbuminuria to the control level and maintained creatinine clearance with enhanced nNOS and eNOS expression compared to quinapril alone.

Antioxidants and dipyridamole inhibit HIV-1 gp120-induced free radical-based oxidative damage to human monocytoid cells

Reactive oxygen species (ROS) may play an important role in HIV-1 pathogenesis and HIV-1 gp120-induced neurotoxicity. Our studies determined the extent to which gp120 increased ROS production in human monocytic U937 cells and the effectiveness of various agents, including dipyridamole (DPR), in blocking these responses. The thiobarbituric acid-reactive substances (TBARS) assay was used as a measure of recombinant gp120 (HIV-1[3B])-induced oxidative damage to U937 cells. As a control, TBARS production was measured using a hypoxanthine/xanthine superoxide generating system. There was gp120-induced oxidative damage in U937 cells with a concentration that produces 50% of maximal effect (apparent EC50 value) of 11 pM. Polyclonal antiserum to gp120 significantly (p < 0.05) inhibited gp120-induced oxidative damage. gp120-induced oxidative damage was significantly inhibited 81% (p < 0.01) by catalase/superoxide dismutase, 53% (p < 0.05) by (+/-)-alpha-tocopherol, 78% (p < 0.01) by desferrioxamine, and 82% (p < 0.01) by ethylene diamine tetraacetic acid (EDTA). These results indicate that gp120 is capable of promoting iron-based oxygen free radical damage to U937 cells. DPR potently (p < 0.05) inhibited both hypoxanthine/xanthine- and gp120-induced oxidative damage with concentrations that produce 50% inhibition (apparent IC50 values) of 1.3 microM for hypoxanthine/xanthine and 1.0 microM for gp120. Therapeutic intervention against ROS production may prevent HIV-1 neurotoxicity.

Are the reactive oxygen-derived species (ROS) interactive properties of the many therapeutic drugs from various categories pertinent to their beneficial effects?

Many pathologic states are known to involve the generation of reactive oxygen species, (ROS). It is not known at present to what extent these phenomena are due to ROS formation, or if their formation is a result of the disease. Many therapeutic drugs either scavenge ROS or inhibit their formation. The purpose of this review is to match the drugs used for certain diseases with their anti-ROS actions. This attempted correlation is made to try to give an answer to the title question.

Inhibition of ferrous-induced lipid peroxidation by dipyridamole, RA-642 and mopidamol in human lung tissue

1. The in vitro production of ferrous-induced lipid peroxidation was 5.71 times higher in rat lung tissue than in human lung membranes. 2. The pyrimido-pyrimidine derivative RA-642 shows a more potent inhibition of ferrous-induced lipid peroxidation than dipyridamole; mopidamol had no effect. All the compounds showed higher anti-peroxidative effect in rat than in human lung tissue.

The pyrimido-pyrimidine derivatives, dipyridamole, mopidamol and RA-642, prevent from retinal vascular defects in experimental diabetes mellitus

We compared the effects of dipyridamole, RA-642, and mopidamol on platelet activity and thromboxane/prostacyclin balance in relation to the degree of retinal vascularization in a model of experimental streptozotocin-induced diabetes in rats. After 3 months, collagen-induced platelet aggregation in whole blood was 25% higher in diabetic animals than in nondiabetics. Dipyridamole inhibited 43% platelet aggregation, mopidamol 39%, and RA-642 36%. Platelet production of thromboxane B2 was 87% higher in untreated diabetic rats. Mopidamol and RA-642 produced a 46% and 41% inhibition of thromboxane B2. Dipyridamole did not inhibited thromboxane B2 synthesis. Aortic production of 6-keto-PGF1 alpha was 43% lower in untreated diabetic animals and showed no change after treatment with either mopidamol or RA-642. In contrast, dipyridamole caused a 90% increase in aortic production of prostacyclin. Computerized analysis of retinal vascularization showed that untreated diabetic rats had a 81% decrease in the area occupied by peroxidase-labelled vessels as compared with nondiabetics. Treatment with dipyridamole, mopidamol, and RA-642 caused 2.5-fold, 2.8-fold and four-fold increases, respectively, in the percentage of retinal surface occupied by peroxidase-labelled vessels. Differences in retinal vascularization between diabetic animals given RA-642 and nondiabetic controls were negligible.

The pyrimido-pyrimidine derivatives, dipyridamole and RA-642, reduce opacification of crystalline lens in diabetic rats

We assessed the effect of dipyridamole, RA-642 and mopidamol, on lenticular opacities in a model of experimental diabetic cataracts in rats. All three pyrimido-pyrimidine derivatives caused a statistically significant reduction of opacification in crystalline lens as compared with untreated diabetic animals. The production of superoxide anions (phenazine methosulphate [PMS]-induced nitroblue tetrazolium [NBT] reduction) showed a decrease of 81.6%, 78.9% and 1.8% in lens tissue homogenates from rats treated with dipyridamole, RA-642 and mopidamol, respectively. Dipyridamole and RA-642 produced a statistically significant inhibition (50% and 64.8%, respectively) of lipid peroxidation (ferrous sulphate and ascorbic acid [FeAs]-induced malondialdehyde [MDA] production) as compared with the group of untreated diabetic rats. Mopidamol did not exert any inhibitory effect on lipid peroxidation. There was a statistically significant correlation between opacification of lens and PMS-induced NBT reduction and FeAs-induced MDA production. We conclude that the protective effect of dipyridamole and RA-642 from free radical damage to crystalline lens in the model of experimental diabetes used in this study, is the result of the antioxidant action of these compounds. The effect exerted by mopidamol, however, suggest a possible complementary effect of the pyrimido-pyrimidine derivatives through interaction with other mechanisms (e.g., the sorbitol pathway) implicated in the development of cataracts.

Oral administration of quercitrin modifies intestinal oxidative status in rats

1. Oral administration of quercitrin to rats for 3 days increases the mucosal glutathione contents in ileum and colon as well as inhibits non-enzymatic lipid peroxidation induced in membrane fractions from jejunal and colonic mucosa. 2. After 7 days of treatment with quercitrin, rat intestinal oxidative status trends to normalize to control rats.

Differential effects of the pyrimido-pyrimidine derivatives, dipyridamole and mopidamol, on platelet and vascular cyclooxygenase activity

The chronic administration of 10 mg/kg/day of dipyridamole to rats produced 33.7% inhibition of platelet aggregation induced with ADP and a 93% increase in 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) in vascular samples, versus saline-treated rats. Mopidamol, 8.3 mg/kg/day, caused 50.6% inhibition of ADP-induced platelet aggregation, 37.6% inhibition of aggregation induced with arachidonic acid, a 47.6% decrease in serum levels of thromboxane B2 and a 23.7% increase in the vascular production of 6-keto-PGF1 alpha, versus saline-treated rats. Dipyridamole showed a higher in vitro anti-aggregating effect in whole blood (IC50 6.6 microM) than in platelet-rich plasma (PRP) (IC50 210 microM), when ADP was used as inducer, and had no effect in the presence of arachidonic acid. Mopidamol exerted a similar effect in whole blood (IC50 3.7-20 microM, depending on the inducer) and PRP (IC50 11-17.3 microM), and showed a dose-dependent inhibition of platelet aggregation and thromboxane B2 synthesis induced with arachidonic acid (IC50 16.8-22.3 microM). Mopidamol also inhibited enzymatically induced lipid peroxidation) (IC50 89 +/- 5.9 mumol/L) and had no effect on free radical-induced lipid peroxidation. The dose-dependent increase in 6-keto-PGF1 alpha in vascular samples after incubation with dipyridamole showed a negative linear correlation with inhibition of lipid peroxidation (r2 = 0.77). It is concluded that the phosphodiesterase inhibitors, dipyridamole and mopidamol, interfere in a different manner with platelet function. It seems that mopidamol may also exert a selective effect on platelet thromboxane synthesis.

Effects of alpha-tocopherol on lipid peroxidation and mitochondrial reduction of tetraphenyl tetrazolium in the rat brain

The antioxidant effect of alpha-tocopherol was assessed in a model of ischemia-reperfusion in the rat brain. In this model, permanent ischemia of the cortical branches of the middle cerebral artery was combined with bilateral occlusion of the common carotid arteries for 1 h and restoration of circulation for a period of 2 h. Lipid peroxidation and mitochondrial reduction of tetraphenyl tetrazolium (TPT) were determined in both untreated and d-alpha-tocopherol treated rats. Ferrous sulfate and ascorbic acid (FeAs) were used to induce lipid peroxidation via the formation of hydroxyl anions. Malondialdehyde (MDA) increased in the ischemia-reperfusion areas (+101%), but FeAs-induced MDA did not vary in the area of permanent ischemia. Brain tissue undergoing ischemia-reperfusion was about 50% less sensitive to the antioxidant effect of ascorbic acid. The reduction of TPT showed 52% mitochondrial damage in the area of ischemia-reperfusion, whereas mitochondrial activity in the area of permanent ischemia was 177 times lower as compared to controls. d-alpha-tocopherol caused a 40% inhibition of MDA production and 16.5% and 21.5% decrease in mitochondrial activity in the areas of ischemia-reperfusion and permanent ischemia, respectively.

The pyrimido-pyrimidine derivative RA-642 protects from brain injury in a combined model of permanent focal ischemia and global ischemia reperfusion

The effects of pyrimido-pyrimidine derivatives (dipyridamole, RA-642 and mopydamole) on lipid peroxidation (inhibition of the production of malondialdehyde, MDA) in different regions of the rat brain were studied. Ferrous sulfate and ascorbic acid (FeAs) were used to induce lipid peroxidation via the formation of hydroxyl anions. The antiperoxidative effect of RA-642 (in the microM range) was 10 times more potent than that of dipyridamole. Mopydamole did not exert any inhibitory effect on MDA production. In a model of ischemia reperfusion with bilateral occlusion of the common carotid arteries for 1 h and restoration of circulation for a period of 2 h, dipyridamole inhibited FeAs-induced MDA production but did not protect from postischemic brain tissue damage (measured by mitochondrial reduction of tetraphenyl tetrazolium). RA-642 inhibited FeAs-induced MDA production and showed 50-67% protection from tissue damage as compared with untreated animals, while mopydamole did not inhibit MDA production and showed 30-48% protection. No correlation was found between inhibition of lipid peroxidation and protection from brain tissue damage.

Effect of dipyridamole with or without aspirin on urine protein excretion in patients with membranous glomerulonephritis

The antiproteinuric effect of the antiplatelet agent dipyridamole has been assessed after inhibition of thromboxane B2 (TxB2) synthesis in 8 patients with confirmed membranous glomerulonephritis. There were three study periods, each of 30 days, and 45 days apart, namely a washout period, treatment with dipyridamole 300 mg/d, and dipyridamole 225 mg/d plus aspirin 150 mg/d. On Days 1 and 30 of each study period serum and urine creatinine, 24-h excretion of protein, creatinine clearance, platelet aggregometry on whole blood and serum TxB2 were measured. Treatment with dipyridamole alone or with aspirin produced significant inhibition of platelet aggregation and a fall in 24-h protein excretion; the latter amounted to 54% with dipyridamole alone and 56% with dipyridamole plus aspirin (NS). Dipyridamole plus aspirin caused an 82% reduction in serum TxB2.

Dipyridamole inhibits platelet aggregation induced by oxygen-derived free radicals

Pyrogallol (a generator of superoxide anions) caused 50% increase in platelet aggregation induced by 400 microM of arachidonic acid. Dipyridamole did not produce a statistically significant inhibition of arachidonic-acid induced platelet aggregation, but it caused 100% inhibition of pyrogallol-stimulated platelet aggregation. Ferrous salts (Fe2+) induced 34% platelet aggregation which was inhibited (79.6%) by a concentration of dipyridamole of 10 microM. Dipyridamole inhibited ferrous-induced lipid peroxidation with IC-50 values of 17.5 microM. When arachidonic acid was used as aggregating agent, the corresponding IC-50 value was 140.5 microM. These results indicate that dipyridamole prevented platelet activation induced by oxygen-derived free radicals.

Inhibition of ferrous-induced lipid peroxidation by pyrimido-pyrimidine derivatives in human liver membranes

The effects of pyrimido-pyrimidine derivatives (dipyridamole, RA-642, and RA-233) on lipid peroxidation, using d-alpha-tocopherol as standard, were studied in enriched membrane fractions from human and rat hepatocytes. Equimolar concentrations of ferrous sulfate and ascorbic acid were used to induce lipid peroxidation. The amount of peroxidized lipids observed in membrane fractions from human liver was smaller than in those from rat liver. In both species, however, pyrimido-pyrimidine derivatives, except for RA-233 in rat liver, inhibited lipid peroxidation dose-dependently in the following sequence: RA-642 greater than dipyridamole greater than d-alpha-tocopherol RA-233.