Kay E. Sarji

Decreased platelet vitamin C in diabetes mellitus: Possible role in hyperaggregation

Abstract To determine whether the handling of Vitamin C in the diabetic might be altered and might relate to the increased platelet sensitivity, we have investigated levels of platelet Vitamin C in the diabetic and determined the effects of Vitamin C in vitro or in vivo on platelet aggregation. Levels of ascorbic acid, as tested by a lingual method, were significantly lower in diabetics than in normals (p in vitro were studied by adding ascorbic acid in buffered solution (pH 7. 35) prior to aggregating agents. Ascorbic acid (1000 μg/ml) in platelet-rich plasma consistently inhibited platelet aggregation with threshold concentrations of ADP, epinephrine, and collagen, but enhanced aggregation with arachidonic acid. With washed platelets, ascorbic acid inhibited arachidonic acid-induced aggregation. To rule out an interaction of ascorbic acid and arachidonic acid in the medium, platelets were incubated at 37°C for 10 minutes with varying concentrations of ascorbic acid, rewashed, and aggregation with arachidonic acid tested. Aggregation was inhibited in a linear dose-dependent fashion. Oral ingestion of ascorbic acid (2 gm/day) for seven days by normal non-smoking males produced a marked inhibition of aggregation. In a similar study, platelets from an insulin-dependent diabetic showed no change in aggregation. These results suggest that platelet levels of ascorbic acid may relate to the hyper-aggregation of platelets from diabetics.

Von Willebrand factor activity in normal subjects: Sex difference and variability

Abstract Variation in levels of activity in the ristocetin assay of “von Willebrand factor (vWF) activity” was investigated in normal individuals under a variety of circumstances. These include levels obtained after an overnight fast, diurnal and daily levels, levels after glucose load, and after mild exercise. One hundred per cent vWF activity was defined by a normal pool. In fasting morning samples, a significant male-female difference in vWF activity was seen (p A significant correlation was seen between vWF activity and fasting glucose levels (p

Abnormalities of platelet aggregation in sickle cell anemia presence of a plasma factor inhibiting aggregation by ristocetin

Abstract Platelet aggregation in plasma from subjects with sickle cell anemia, not in crisis, was tested using the aggregometer. Aggregation induced by adenosine diphosphate (ADP), epinephrine, or collagen was decreased in platelet-rich plasma (PRP) from these subjects. Aggregation induced by ristocetin (1.09 mg/ml final conc.) was absent or was preceded by a lag phase in sickle cell PRP but not in normal PRP. Washed platelets from subjects with sickle cell anemia mixed with normal platelet-poor plasma (PPP) showed normal ristocetin-induced aggregation. Washed normal platelets mixed with sickle cell PPP showed progressive inhibition of ristocetin aggregation with increasing amounts of plasma. Dilution of the sickle cell PPP or increasing the final concentration of ristocetin to 2.4 mg/ml resulted in normal aggregation. Factor VIII antigen levels (196±16% S.E.M.) and factor VIII procoagulant activity (286±82%) were elevated in sickle cell plasma. Fibrinogen levels (239±42 mg%) were normal or slightly decreased; no relationship to aggregation was seen. These results suggest that an abnormally high factor VIII antigen/von Willebrand factor activity ratio is present in sickle cell anemia. It is postulated that inhibition of ristocetin-induced platelet aggregation by sickle cell plasma is related to competition for available ristocetin.

Heparin-induced platelet aggregation in burn patients

Abstract Platelets from patients with thermal injury were studied to evaluate the effect of beef lung and intestinal mucosal heparin upon platelet aggregation. In contrast to controls, 15% of samples from burn patients demonstrated spontaneous aggregation, and 60% showed either first or second phase aggregation after exposure to either heparin preparation. No difference was observed between burn patient and normal control platelets in their aggregation response to ADP. Increased spontaneous and heparin-induced aggregation seen in burn patient platelet-rich plasma could not be correlated with platelet count, sampling time, or plasma factors. The enhanced response to heparin seen in these patients appears to be intrinsic to the platelet.

THE EFFECT OF ORAL GLUCOSE ON VON WILLEBRAND FACTOR ACTIVITY IN NORMAL AND DIABETIC SUBJECTS

We have previously noted increased platelet aggregation and high von Willebrand factor activity in patients with chemical diabetes. In this paper we have studied platelet aggregation, plasma glucose, insulin, free fatty acids, growth hormone, and von Willebrand factor activity during the glucose tolerance test in six normal and six chemical diabetic subjects. The results suggest that von Willebrand factor activity is suppressed coincident with the rise of glucose and insulin and provide further evidence of hormonal and metabolic control of levels of von Willebrand factor activity.

Rationale for Antiplatelet Agents in Diabetic Vascular Disease

Studies summarized in this paper indicate that some diabetics have increased sensitivity to platelet aggregating agents. The problem is in the platelet release reaction and may reflect increased synthesis of prostaglandins or their precursors. An interaction of plasma factor such as von Willebrand factor with platelets may also be involved. Based on these and other considerations, a prospective study on the use of aspirin and dipyridamole on diabetic lower extremity vascular disease is underway as a Veterans Administration Cooperative Study.

Platelet lipoproteins. A comparative study with serum lipoproteins.

The nature of human platelet lipoproteins was studied in two series of experiments. In the first series, whole platelets were utilized for extraction of lipoproteins by three different methods: chloroform/methanol/phenol; saline; or sucrose-gradient ultracentrifugation of platelet homogenates. By polyacrylamide gel electrophoresis we were able to demonstrate the existence of lipoprotein in the extracts obtained by the last two methods. These lipoproteins were found not to share antigenic determinants with alpha and beta serum lipoproteins. The second series of experiments utilized platelets solubilized either in sodium deoxycholate or sodium dodecyl sulfate. The solubilized product was characterized by double immunodiffusion and polyacrylamide gel electrophoresis. The nonidentity between plasma and platelet lipoproteins previously demonstrated in the first series of experiments was confirmed. This nonidentity was also supported by a comparison between the apoproteins of purified serum lipoproteins and platelet proteins released after solubilization with sodium dodecyl sulfate. No identical protein fractions were found. Our results suggest that, unlike erythrocyte membrane lipoproteins, the platelet lipoproteins are structurally different from plasma lipoproteins.