Antiplatelet effects of prostacyclin and nitric oxide in patients with type I diabetes and ischemic or edematous retinopathy

Platelet Oxidative Stress and its Relationship with Cardiovascular Diseases in Type 2 Diabetes Mellitus Patients

Enhanced platelet activation and thrombosis are linked to various cardiovascular diseases (CVD). Among other mechanisms, oxidative stress seems to play a pivotal role in platelet hyperactivity. Indeed, upon stimulation by physiological agonists, human platelets generate and release several types of reactive oxygen species (ROS) such as O2 -, H2O2 or OH-, further amplifying the platelet activation response via various signalling pathways, including, formation of isoprostanes, Ca2+ mobilization and NO inactivation. Furthermore, excessive platelet ROS generation, incorporation of free radicals from environment and/or depletion of antioxidants induce pro-oxidant, pro-inflammatory and platelet hyperaggregability effects, leading to the incidence of cardiovascular events. Here, we review the current knowledge regarding the effect of oxidative stress on platelet signaling pathways and its implication in CVD such as type 2 diabetes mellitus. We also summarize the role of natural antioxidants included in vegetables, fruits and medicinal herbs in reducing platelet function via an oxidative stress-mediated mechanism.

An Overview of Our Current Understanding of Diabetic Macular Ischemia (DMI)

Diabetic macular ischemia (DMI) is a troublesome complication of diabetes mellitus. The pathogenesis, progression, consequences, and treatment options for this disease are still poorly understood. However, it is believed that this complication is associated with several risk factors like poor glycemic control and high blood pressure. Two factors have been identified in the pathogenesis of the disease that play pivotal roles in disease development and progression. One of these factors includes extensive damage to the microvasculature of the retina. This includes narrowing of the vascular lumen and extensive damage to the endothelial cells, pericytes and the extracellular matrix. The second factor includes extensive damage to the neurosensory layer of the retina. DMI is always associated with other complications of diabetic retinopathy like retinal edema, so it is very difficult to find an isolated case of DMI. Moreover, the condition is also very rare making it very difficult to study and diagnose. However, a number of diagnostic tests like optical coherence tomography (OCT), fluorescence angiography (FA), and perimetry can be used as tools for the early detection of DMI. Since this disease damages the retina, loss of vision is an inevitable consequence that can progressively worsen over time. Also, DMI has been implicated as a risk factor for retinal edema and progressive diabetic retinopathy. Until now, no defined treatment protocol has been devised. The only available treatments focus on the management of risk factors (hyperglycemia and hypertension). Still, many aspects of DMI remain poorly studied and understood. This review paper aims to add to our current understanding of diabetic macular ischemia (DMI).

Neuroprotective Effect of Hydroxytyrosol in Experimental Diabetic Retinopathy: Relationship with Cardiovascular Biomarkers

The aim of the study was to test the neuroprotective effect of hydroxytyrosol (HT) on experimental diabetic retinopathy. Animals were divided in four groups: (1) control nondiabetic rats, (2) streptozotocin-diabetic rats (DR), (3) DR treated with 1 mg/kg/day p.o. HT, and (4) DR treated with 5 mg/kg/day p.o. HT. Treatment with HT was started 7 days before inducing diabetes and was maintained for 2 months. In the DR group, total area occupied by extracellular matrix was increased, area occupied by retinal cells was decreased; both returned to near-control values in DR rats treated with HT. The number of retinal ganglion cells in DR was significantly lower (44%) than in the control group, and this decrease was smaller after HT treatment (34% and 9.1%). Linear regression analysis showed that prostacyclin, platelet aggregation, peroxynitrites, and the dose of 5 mg/kg/day HT significantly influenced retinal ganglion cell count. In conclusion, HT exerted a neuroprotective effect on diabetic retinopathy, and this effect correlated significantly with changes in some cardiovascular biomarkers.

The effect of reactive oxygen species on whole blood aggregation and the endothelial cell-platelet interaction in patients with coronary heart disease

Background

The effect of reactive oxygen species (ROS) on platelet function in coronary heart disease (CHD) is complex and poorly defined. Platelet aggregation studies in healthy volunteers have demonstrated contrasting results when platelets are exposed to ROS. We investigated the effect of ROS on whole blood aggregation (WBA) and the endothelial cell-platelet interaction in patients with CHD.

Methods and Results

ROS generated by xanthine and xanthine oxidase caused a concentration-dependent inhibition of WBA in blood from healthy donors and patients with CHD. In patients with CHD, 100 μM xanthine and 100 mU/ml xanthine oxidase inhibited WBA in response to 3 μg/ml collagen by 28.9% (95% CI 15.9%-41.8%, p < 0.001) and in response to 5 μM ADP by 36.0% (95% CI 9.6%-62.4%, p = 0.005). Using nitrotyrosine expression, platelets isolated from patients with CHD were found to be susceptible to peroxynitrite damage. The addition of 1 × 10⁵ cultured endothelial cells inhibited WBA in response to 3 μg/ml collagen by 31.2% (95% CI 12.2%-50.2%, p < 0.05) and in response to 5 μM ADP by 31.6% (95% CI 2.5-60.7%, p < 0.05). Addition of xanthine and xanthine oxidase did not alter this effect, however pre-treatment of endothelial cells with a nitric oxide synthase inhibitor (L-NAME) partly reversed the inhibition.

Conclusion

ROS inhibit WBA in blood from patients with CHD. Whilst endothelial cells also inhibit WBA, the effect is attenuated by L-NAME, suggesting that nitric oxide is likely to remain an important protective mechanism against thrombosis in CHD.

Effects of terutroban, a thromboxane/prostaglandin endoperoxide receptor antagonist, on retinal vascularity in diabetic rats

BACKGROUND

The aim of the present study is to investigate the effectiveness of terutroban, a selective antagonist of the thromboxane/prostaglandin endoperoxide receptor, in preventing retinal ischaemia in a model of diabetes in rats.

METHODS

Experimental diabetes was induced with streptozotocin. Rats were distributed into five groups (n = 20): (1) non-diabetic rats, (2) rats with diabetes (DR) treated with vehicle, (3) DR treated with aspirin (2 mg/kg/day p.o.), (4) DR treated with terutroban (5 mg/kg/day p.o.), (5) DR treated with terutroban (30 mg/kg/day p.o.). The follow-up period was 3 months. The main assessment was the percentage of retinal surface covered with vessels permeable to peroxidase. Platelet aggregation, aortic prostacyclin and nitric oxide production, plasma levels of lipid peroxides (thiobarbituric-acid-reactive substances) and 3-nitrotyrosine and serum levels of IL-6 were evaluated.

RESULTS

Diabetes induced a reduction in retinal vascularity (76.9%), aortic prostacyclin (37.8%) and nitric oxide production (35.0%), and increased platelet aggregation, lipid peroxides, 3-nitrotyrosine. When compared with vehicle-treated DR, terutroban increased the percentage of retinal surface covered by PVPP (38% for terutroban-5 and 61% for terutroban-30), aortic prostacyclin (188% for terutroban-5 and 146% for terutroban-30) and nitric oxide production (320% for terutroban-5 and 390% for terutroban-30). Moreover, terutroban reduced platelet reactivity (27.8–95.1%, according to the inducer), lipid peroxides (60.7% for terutroban-5 and 50.0% for terutroban-30), 3-nitrotyrosine (43.8% for terutroban-5 and 36.8% for terutroban-30) and IL-6 concentration (18.0% for terutroban-30). The effect of terutroban in retinal, nitrosative and aortic parameters was significantly higher than that of aspirin.

CONCLUSIONS

Terutroban significantly protected retinal vascularity from ischaemia in experimental diabetes, and this result could be attributed not only to its antiplatelet/antithrombotic activities but also to its vascular properties.

Virgin olive oil administration improves the effect of aspirin on retinal vascular pattern in experimental diabetes mellitus

The aim of the present study is to evaluate the possible influence of virgin olive oil (VOO) on the effect of acetylsalicylic acid (ASA) in platelet aggregation, prostanoid and NO production and retinal vascular pattern in rats with experimental type 1-like diabetes. We used 100 male Wistar rats that were distributed into five groups: (1) non-diabetic rats (NDR); (2) untreated diabetic rats (DR); (3) DR treated with ASA (2 mg/kg per d per os (p.o.)); (4) DR treated with VOO (0·5 ml/kg per d p.o.); (5) DR treated with ASA plus VOO. The duration of diabetes was 3 months, and each treatment was administered from the first day of diabetes. Variables that were quantified were platelet aggregation (Imax), thromboxane B2 (TxB2), aortic prostacyclin (6-keto-PGF1α) and NO, and the percentage of retina with horseradish peroxidase-permeable vessels (HRP-PV). Diabetic rats showed a higher Imax (35 %) and TxB2 (63 %) than NDR, and a lower 6-keto-PGF1α, NO and HRP-PV than NDR ( − 74·6 %). ASA and VOO administration reduced these differences and prevented the percentage of HRP-PV ( − 59·7 % with ASA and − 46·7 % with VOO). The administration of ASA plus VOO showed a strong platelet inhibition (80·2 v. 23·4 % for VOO and 50·6 % for ASA+VOO, P < 0·0001), and reduced HRP-PV differences to − 31·6 % (P < 0·001 with respect to DR and P < 0·0001 with respect to DR treated with ASA). In conclusion, the administration of VOO to rats with type 1-like diabetes mellitus improves the pharmacodynamic profile of ASA, and increases its retinal anti-ischaemic effect.

Pro-healing drug-eluting stents: a role for antioxidants?

Current strategies to lower the incidence of ISR (in-stent restenosis) following PCI (percutaneous coronary intervention) are aimed at modifying arterial healing after stent injury. This can impair endothelial recovery and render the vessel prone to acute thrombosis. As early restoration of endothelial integrity inhibits neointimal growth and thrombosis, alternative approaches which encourage this process may provide a more effective long-term result after PCI. Oxidative stress is enhanced after PCI and participates in the regulation of endothelial regeneration and neointimal growth. Moreover, evidence suggests antioxidants improve re-endothelialization and inhibit ISR. By promoting, rather than blocking, the healing process, antioxidant and other therapies may offer an alternative or additional approach over the antiproliferative approaches common to many current devices.

Effects of hypoxia reoxygenation in brain slices from rats with type 1-like diabetes mellitus

BACKGROUND

The aim of this study was to determine whether the brain tissue of type 1 diabetic animals is more susceptible to damage by hypoxia reoxygenation than healthy animals.

METHODS

This study used rats with diabetes of 1, 2 and 3 months (N = 15 rats/group). Brain slices were subjected to hypoxia and reoxygenation for 180 min in vitro. We measured oxidative stress (lipid peroxidation, glutathione concentration and enzyme activities related to glutathione), concentration of prostaglandin E(2) (PGE(2)) and nitric oxide (NO) pathway (nitrite + nitrate, activities of constitutive (cNOS) and inducible (iNOS) nitric oxide synthase). As a parameter of cell death we measured the efflux of lactate dehydrogenase (LDH).

RESULTS

After reoxygenation LDH activity increased in comparison to nondiabetic animals by 40, 40.6 and 68.9% in animals with diabetes of 1, 2 and 3 months duration, respectively. These changes were accompanied by greater increases in lipid peroxides (25.4, 93.7 and 92.8%). PGE(2) accumulated in significantly larger amounts in diabetic animals (62.5, 85.5 and 114%), and nitrite + nitrate accumulation was significantly greater in rats with diabetes of 2 (40.2%) and 3 months duration (24.0%). iNOS activity increased significantly in all the groups of diabetic animals, with the largest increases in rats with diabetes of 2 (18.6%) and 3 months duration (21.1%).

CONCLUSIONS

The biochemical pathways involved in oxidative stress and neuronal death are more sensitive to hypoxia reoxygenation in type 1-like diabetic, as compared to normal, rats.

Influence of glucose concentration on the effects of aspirin, ticlopidine and clopidogrel on platelet function and platelet–subendothelium interaction

Clinical studies have shown that the ability of aspirin to prevent cerebrovascular accidents is weaker in patients with diabetes. The aim of this study was to determine whether high concentrations of glucose modified the effect of aspirin, ticlopidine and clopigodrel on platelet function and platelet-subendothelium interactions. This in vitro study tested three different concentrations of glucose. The effects were analyzed by comparing platelet aggregometry in whole blood, nitric oxide and prostacyclin production in cultures of human endothelial cells, and by quantitative analysis of morphological features of the platelet-subendothelium interaction under flow conditions. High concentrations of glucose increased platelet aggregation (13.9 Omega with 5 mM glucose vs. 21.6 Omega with 16.6 mM) and platelet-subendothelium interactions (28.9% with 5 mM glucose vs.35.2% with 16.6 mM), and decreased nitric oxide and prostacyclin production. In the presence of high concentrations of glucose, the antiaggregant effect of aspirin and its influence on nitric oxide production were diminished (IC50 54 microM with 5 mM glucose vs.556 microM with 16.6 mM glucose), and its effect on the platelet-subendothelium interaction was reduced (10.5% platelet occupancy with 5 mM glucose vs.23% with 16.6 mM glucose). The effects of ticlopidine and clopidogrel were not significantly modified.

Nitric oxide-cGMP and prostacyclin-cAMP pathways in patients with type II diabetes and different types of retinopathy

The aim of this study was to investigate two factors of endothelial dysfunction and their platelet second messengers in patients with type II diabetes and different types of retinopathy. We compared 20 healthy volunteers and 117 patients with type II diabetes (34 with no signs of diabetic retinopathy, 26 with background diabetic retinopathy, 29 with ischemic-proliferative diabetic retinopathy and 28 with edematous diabetic retinopathy). The following parameters were recorded: platelet aggregometry, nitrites, 6-keto-prostaglandin-F(1alpha) and intraplatelet cAMP and cGMP. Platelet aggregation was greater in patients with diabetic retinopathy. The concentration of ADP that produced 50% maximum intensity of aggregation was 1.81 microM in patients without diabetic retinopathy, 0.92 microM in patients with background diabetic retinopathy, 0.85 microM in patients with ischemic-proliferative diabetic retinopathy and 0.44 microM in patients with edematous diabetic retinopathy. The platelets in these patients were more resistant to inhibition by SIN-1 (concentrations of SIN-1 that produced 50% inhibition of maximum intensity of collagen-induced aggregation in the four patient groups: 18.1, 13.6, 16.2 and 33.2 microM, respectively). Nitrite concentration in patients with ischemic-proliferative diabetic retinopathy was one sixth of the value in healthy controls, but there was no significant difference between the control group and patients with edematous diabetic retinopathy. In the latter group, neutrophils increased nitrite production by 68.7 +/- 3%, whereas in patients with ischemic-proliferative diabetic retinopathy, this increase was 18.7 +/- 2.0%. We conclude that nitric oxide production is higher in patients with type II diabetes and edematous retinopathy than in those with ischemic-proliferative retinopathy. This finding, together with the possibly greater production of free radicals, may explain the greater impairment of platelet function in the former patients.