Carlo Giammarresi

Inhibition of Thromboxane Biosynthesis and Platelet Function by Simvastatin in Type IIa Hypercholesterolemia

Abstract Thromboxane A2 (TXA2) biosynthesis is enhanced in the majority of patients with type IIa hypercholesterolemia. Because simvastatin (a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor) was previously shown to reduce platelet aggregation and TXB2 production ex vivo, we investigated TXA2 biosynthesis and platelet function in 24 patients with type IIa hypercholesterolemia randomized to receive in a double-blind fashion simvastatin (20 mg/d) or placebo for 3 months. The urinary excretion of 11-dehydro-TXB2, largely a reflection of platelet TXA2 production in vivo, was measured by a previously validated radioimmunoassay technique. Blood lipid levels and urinary 11-dehydro-TXB2 excretion were significantly ( P <.001) reduced by simvastatin. In contrast, placebo-treated patients did not show any statistically significant changes in either blood lipids or 11-dehydro-TXB2 excretion. The reduction in 11-dehydro-TXB2 associated with simvastatin was correlated with the reduction in total cholesterol ( r =.81, P <.0001), LDL cholesterol ( r =.79, P <.0001), and apolipoprotein B ( r =.76, P <.0001) levels. Platelets from patients with type IIa hypercholesterolemia required significantly ( P <.01) more collagen and ADP to aggregate and synthesized less TXB2 in response to both agonists after simvastatin therapy. Bleeding time, platelet sensitivity to Iloprost, and blood lipoprotein(a) and HDL cholesterol levels were not significantly affected by either treatment. We conclude that enhanced TXA2 biosynthesis in type IIa hypercholesterolemia is, at least in part, dependent on abnormal cholesterol levels and/or other simvastatin-sensitive mechanisms affecting platelet function.

Diabetes Mellitus, Hypercholesterolemia, and Hypertension but Not Vascular Disease Per Se Are Associated With Persistent Platelet Activation In Vivo Evidence Derived From the Study of Peripheral Arterial Disease

BACKGROUND Previous studies relating increased thromboxane (TX) biosynthesis to cardiovascular risk factors do not answer the question whether platelet activation is merely a consequence of more prevalent atherosclerotic lesions or reflects the influence of metabolic and hemodynamic disturbances on platelet biochemistry and function. METHODS AND RESULTS We examined 64 patients with large-vessel peripheral arterial disease and 64 age- and sex-matched control subjects. TXA2 biosynthesis was investigated in relation to cardiovascular risk factors by repeated measurements of the urinary excretion of its major enzymatic metabolite, 11-dehydro-TXB2, by radioimmunoassay. Urinary 11-dehydro-TXB2 was significantly (P = .0001) higher in patients with peripheral arterial disease (57 +/- 26 ng/h) than in control subjects (26 +/- 7 ng/h). Seventy percent of patients had metabolite excretion > 2 SD above the normal mean. However, 11-dehydro-TXB2 excretion was enhanced only in association with cardiovascular risk factors. Multivariate analysis showed that diabetes, hypercholesterolemia, and hypertension were independently related to 11-dehydro-TXB2 excretion. During a median follow-up of 48 months, 8 patients experienced major vascular events. These patients had significantly (P = .001) higher 11-dehydro-TXB2 excretion at baseline than patients who remained event free. CONCLUSIONS The occurrence of large-vessel peripheral arterial disease per se is not a trigger of platelet activation in vivo. Rather, the rate of TXA2 biosynthesis appears to reflect the influence of coexisting disorders such as diabetes mellitus, hypercholesterolemia, and hypertension on platelet biochemistry and function. Enhanced TXA2 biosynthesis may represent a common link between such diverse risk factors and the thrombotic complications of peripheral arterial disease.

Inhibition of thromboxane biosynthesis and platelet function by indobufen in type II diabetes mellitus

Indobufen is a reversible inhibitor of platelet prostaglandin G/H-synthase. To verify the dose dependence of the antiplatelet effect of indobufen on ex vivo and in vivo indexes of thromboxane (TX) biosynthesis and TXA2-dependent platelet function, we studied nine patients with non-insulin-dependent diabetes mellitus (NIDDM). This was a randomized, double-blind, crossover study in which each patient was treated with three different daily regimens (50 mg BID, 100 mg BID, and 200 mg BID) of indobufen for 1 week, with a 7-day washout period between treatments. Urinary 11-dehydro-TXB2 excretion averaged 58.2 +/- 21.8 ng/h at baseline. TX metabolite excretion was reduced dose dependently by indobufen: by 67% at 50 mg BID, 72% at 100 mg BID, and 81% at 200 mg BID. Platelet cyclooxygenase activity, ATP release, collagen-induced platelet aggregation, and bleeding time also were modified dose dependently by indobufen. Biochemical demonstration of suppressed platelet TXA2 in vivo was accompanied by evidence of inhibited platelet function as assessed ex vivo. Under pathophysiological conditions, such as NIDDM, which are associated with enhanced TXA2 synthesis, more than 95% suppression of platelet cyclooxygenase activity may be necessary to produce virtually maximal inhibition of platelet TXA2 biosynthesis in vivo.

Increased plasminogen activator inhibitor antigen levels in diabetic patients with stable angina.

PAI-L antigen, tPA antigen and thrombin - antithrombin III complexes (TAT) levels were measured in 10 males with stable angina and type-D diabetes mellitus and in 16 males with stable angina without diabetes or other risk factors (hyperfibrinogenaemia, hyperlipidaemia, diabetes, hypertension, smoking and obesity) known to increase PAI levels. Ten healthy men of equivalent age served as controls. Because only diabetics with coronary artery disease (CAD) showed a decreased fibrinolytic capacity, a second study was performed on the 16 non-diabetic CAD patients to determine whether submaximal workload induces significant changes of tPA and PAI levels. TAT levels were increased in CAD, and significantly so in the diabetic group. tPA levels were increased only in CAD patients without diabetes. PAI levels were significantly increased in diabetic CAD patients (5.26 ± 1.96 ng/ml) but not in the stable angina patients without diabetes (2.97 ± 1.44 ng/ml). ImmunologicaUy-reactive tPA released after exercise was higher in the 16 CAD patients without diabetes than in controls. Our data could indicate that in stable angina without diabetes there is no chronic latent activation of the clotting system, with no impairment of fibrinolytic activity. On the other hand, the presence of diabetes mellitus seems to influence the fibrinolytic capacity in CAD, particularly increasing PAI levels.

Heparin induces an accumulation of atherogenic lipoproteins during hemodialysis in normolipidemic end-stage renal disease patients

Dyslipidemias may account for the excess of cardiovascular mortality in end‐stage renal disease (ESRD). Lipoprotein studies in ESRD patients are usually relative to prehemodialysis samples even if significative changes may occur after dialysis. In this study, we aimed to investigate the effects of ESRD on triglyceride‐rich lipoproteins (TRL) subpopulations distribution and acute change following hemodialytic procedures, including the relative contribution of heparin administration. We selected a group of normolipidemic male middle‐aged ESRD patients free of any concomitant disease affecting lipoprotein remnant metabolism compared with controls. We separated TRL subfractions according to density and apoE content and evaluated the changes of these particles after hemodialytic procedures with or without heparin. ESRD subjects had higher TRL subfractions, with the exception of apoE‐rich particles, lower high‐density lipoprotein (HDL) largest subclasses, and a smaller low‐density lipoprotein peak particle size than controls. After a hemodialytic standard procedure with heparin, we demonstrated a significant reduction of triglyceride, an increase of HDL‐cholesterol levels, and a raise of small very‐low‐density lipoprotein, intermediate‐density lipoproteins (IDL), apoE‐rich particles, and non‐HDL‐cholesterol levels. When hemodialysis was performed without heparin, no significant changes were observed. In the absence of concomitant hyperlipidemic triggers, ESRD patients show significant lipoprotein abnormalities before dialysis, but without any increased remnant particles concentrations. We speculate that hemodialysis, in particular heparin administration during this procedure, leads to a massive atherogenic TRLs production because of the acute stimulation of the dysfunctional lipolytic system not followed by an efficient removal, determining a recurrent lipoprotein remnant accumulation.

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.