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

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.

Platelet hemostasis in patients with metabolic syndrome and type 2 diabetes mellitus: cGMP- and NO-dependent mechanisms in the insulin-mediated platelet aggregation

Patients with metabolic syndrome (MetS) and type 2 diabetes mellitus (T2DM) have high risk of microcirculation complications and microangiopathies. An increase in thrombogenic risk is associated with platelet hyperaggregation, hypercoagulation, and hyperfibrinolysis. Factors leading to platelet activation in MetS and T2DM comprise insulin resistance, hyperglycemia, non-enzymatic glycosylation, oxidative stress, and inflammation. This review discusses the role of nitric oxide (NO) in the regulation of platelet adhesion and aggregation processes. NO is synthesized both in endotheliocytes, smooth muscle cells, macrophages, and platelets. Modification of platelet NO-synthase (NOS) activity in MetS patients can play a central role in the manifestation of platelet hyperactivation. Metabolic changes, accompanying T2DM, can lead to an abnormal NOS expression and activity in platelets. Hyperhomocysteinemia, often accompanying T2DM, is a risk factor for cardiovascular accidents. Homocysteine can reduce NO production by platelets. This review provides data on the insulin effects in platelets. Decrease in a number and sensitivity of the insulin receptors on platelets in T2DM can cause platelet hyperactivation. Various intracellular mechanisms of anti-aggregating insulin effects are discussed. Anti-aggregating effects of insulin are mediated by a NO-induced elevation of cGMP and upregulation of cAMP- and cGMP-dependent pathways. The review presents data suggesting an ability of platelets to synthesize humoral factors stimulating thrombogenesis and inflammation. Proinflammatory cytokines are considered as markers of T2DM and cardiovascular complications and are involved in the development of dyslipidemia and insulin resistance. The article provides an evaluation of NO-mediated signaling pathway in the effects of cytokines on platelet aggregation. The effects of the proinflammatory cytokines on functional activity of platelets are demonstrated.

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.

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.