Isabella Catalano

Thromboxane Biosynthesis and Platelet Function in Type II Diabetes Mellitus

It has been suggested that platelet hyperreactivity in patients with diabetes mellitus is associated with increased platelet production of thromboxane. We therefore compared the excretion of a thromboxane metabolite and platelet function in 50 patients with Type II diabetes mellitus who had normal renal function and clinical evidence of macrovascular disease and in 32 healthy controls. The mean (+/- SD) excretion rate of urinary 11-dehydro-thromboxane B2 was significantly higher in the patients than in the controls (5.94 +/- 3.68 vs. 1.50 +/- 0.79 nmol per day; P less than 0.001), irrespective of the type of macrovascular complication. Tight metabolic control achieved with insulin therapy reduced the levels of 11-dehydro-thromboxane B2 by approximately 50 percent. The fractional conversion of exogenous thromboxane B2 (infused at a rate of 4.5, 45.3, or 226.4 fmol per kilogram of body weight per second) to urinary 11-dehydro-thromboxane B2 was assessed in four patients, in whom it averaged 5.4 +/- 0.1 percent; this value did not differ from that measured in healthy subjects. Aspirin in low doses (50 mg per day for seven days) reduced urinary excretion of the metabolite by approximately 80 percent in four patients. The fact that thromboxane biosynthesis recovered over the following 10 days was consistent with a platelet origin of the urinary metabolite.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased thromboxane biosynthesis in type IIa hypercholesterolemia.

BackgroundIncreased platelet thromboxane (TX)A2 production has been described in type IIa hypercholesterolemia. To verify the relevance of these capacity-related measurements to the actual rate of TXA2 biosynthesis in vivo, we studied the urinary excretion of its major enzymatic metabolites in 46 patients with type hIa hypercholesterolemia and 20 age-matched controls. Methods and ResultsUrinary 11-dehydro-TXB2 and 2,3-dinor-TXB2 were measured by previously validated radioimmunoassays. The excretion rate of 11-dehydro-TXB2 was significantly (p < 0.001) higher in patients (68.7±35.1 ng/hr, mean±SD) than in controls (22.4±9.4 ng/hr), with metabolite excretion >2 SD of the normal mean in 74% of the patients. Urinary 11-dehydro-TXB2 was significantly (p < 0.01) correlated with the threshold aggregating concentration of collagen (r = −0.641) and arachidonate (r = −0.734) and with agonist-induced platelet TXB2 production in vitro (r = 0.647 and 0.748, respectively). Moreover, a statistically significant correlation (r = 0.673, p < 0.001, n = 66) was found between 11-dehydro-TXB2 excretion and total plasma cholesterol. The enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor simvastatin (20 mg/day for 6 months) significantly reduced cholesterol levels by 22–28% and urinary 11-dehydro-TXB2 excretion by 32–42% in 10 patients. However, the reduction in the latter did not correlate with the reduction in the former and may have resulted from a nonspecific effect of simvastatin. Moreover, selective inhibition of platelet cyclooxygenase activity by low-dose aspirin (50 mg/day for 7 days) was associated with cumulative inhibition of 11-dehydro-TXB2 excretion by approximately 70% in six patients. ConclusionsTXA2 biosynthesis is enhanced in the majority of patients with type lla hypercholesterolemia; this is, at least in part, a consequence of abnormal cholesterol levels, as suggested by the correlation between the two. Low-dose aspirin can largely suppress increased metabolite excretion, thus suggesting that it reflects TXA2-dependent platelet activation in vivo.

Thrombin-antithrombin III complexes in type II diabetes mellitus

Several studies suggest that diabetes is associated with a hypercoagulable state. Therefore determination of thrombin-antithrombin complex (TAT) could represent a sensitive parameter for specific detection of a latent activation of the clotting system. The present study documents increased plasma TAT in a heterogeneous group of non-insulin-dependent diabetic patients. The finding of increased TAT levels both in diabetic patients with vascular complications and in vascular disease patients without diabetes suggests a relationship between existing vascular disease and the hemostatic mechanism that produces augmented thrombin activity. In acute vascular occlusions the presence of diabetes seems to increase activation of the coagulative system.

Effects of defibrotide on fibrinolytic activity in diabetic patients with stable angina pectoris

18 type II diabetes mellitus patients with coronary artery disease (CAD) have been studied. Tissue plasminogen activator (t-PA) antigen and activity, plasminogen activator inhibitor (PAI) antigen and activity, thrombin-antithrombin III (TAT) complexes were determined in blood samples. Diabetic CAD patients showed higher TAT levels with clearly increased PAI levels whereas t-PA levels levels were similar in patients and controls. Long term defibrotide treatment induced marked changes in fibrinolytic parameters of these diabetic patients with CAD with increased t-PA activity, that could be related to an evident reduction of PAI antigen and activity. Drugs able to modulate PAI activity may be useful in clinical conditions at high risk of thrombotic vascular complications like diabetics with stable angina.

Platelet Function During Ticlopidine and Eicosapentaenoic Acid Administration in Patients with Coronary Heart Disease

Antiplatelet drugs have been reported to be useful in unstable angina. This study was designed to investigate the effects of simultaneous administration of ticlopidine and eicosapentaenoic acid (EPA) on platelet function in coronary heart disease (CHD) patients. Ticlopidine significantly reduced platelet aggregation induced by ADP and collagen with no effect on arachidonate metabolism. The aggregation responses to collagen, ADP and arachidonate were not altered significantly by EPA (as fish oil) intake whereas thromboxane A(2) formation was reduced, but not completely inhibited. Combined therapy seems to achieve a more marked degree of inhibition of aggregation together with a fall in the urinary excretion of 11-dehydrothromboxane B(2) metabolite. Therefore, in CHD patients ticlopidine therapy plus fish oil administration could be useful to inhibit two different mechanisms (TxA(2)- and ADP-dependent) of platelet activation.

Platelet aggregation, ATP release and cytoplasmic Ca2+ movement: The effects of cloricromene

A placebo-controlled, double-blind, randomized, cross-over study was performed in 24 healthy volunteers. 12 volunteers received Cloricromene (100mg gastroresistant capsules twice a day) for 7 days, the other volunteers received identical placebo capsules. Subsequently, after a 7-day wash-out period, at day 15, each subject received the other treatment. Blood samples were taken on days 1 and 15 (1st day of each treatment) as well as on days 7 and 21 (7th day of each treatment) before the morning drug administration and 2 and 4 hours later. Platelet aggregation and ATP secretion were studied in whole blood (WB) using ADP and collagen as stimulating agents. Ca2+ fluxes were studied in aequorin-loaded, washed platelets stimulated with ADP and collagen, while aggregation in platelet-rich plasma (PRP) was studied using PAF, ADP and adrenaline as agonists. Consistent inhibition of aggregation and release induced by both ADP and collagen was observed in WB after Cloricromene administration. Similarly, Ca2+ flux was also inhibited after drug administration. Platelet aggregation in PRP was inhibited only after 7 days of Cloricromene treatment with ADP and adrenaline as stimuli. We conclude that oral administration of Cloricromene leads to significant antiplatelet activity in healthy volunteers, in particular when platelets are studied in the presence of other blood elements.

Fibrinogen and von Willebrand factor in type II diabetes mellitus

A hypercoagulable state may contribute to the formation of early vascular lesions in diabetes. The von Willebrand factor is required for the attachment of platelets to the subendothelium; fibrinogen is required for platelet aggregation. This study was designed to assess in type II diabetic patients plasma levels of fibrinogen and von Willebrand factor to see if these variables are associated with platelet aggregation responses to adenosine diphosphate (ADP). Fibrinogen and the von Willebrand factor were significantly increased in diabetics but only fibrinogen was significantly related to platelet aggregation for ADP. Strict metabolic control does not reduce the increased concentrations of these two proteins. Hyperfibrinogenaemia was related to the presence of macrovascular disease. Therefore measurements of plasma fibrinogen could be added to the cardiovascular risk factor profile of diabetic patients. Intervention studies are also needed to reduce the increased incidence of thrombotic diseases in patients with diabetes mellitus.