Background-F 2 isoprostanes are stable, free radical-catalyzed products of arachidonic acid that reflect lipid peroxidation in vivo. Methods and Results-Specific assays were developed by use of mass spectrometry for the F 2 isoprostanes iPF 2␣ -III and iPF 2␣ -VI and arachidonic acid (AA). Urinary excretion of the 2 F 2 isoprostanes was significantly increased in hypercholesterolemic patients, whereas substrate AA in urine did not differ between the groups. iPF 2␣ -III (pmol/mmol creatinine) was elevated (PϽ0.0005) in homozygous familial hypercholesterolemic (HFH) patients (85Ϯ5.5; nϭ38) compared with age-and sex-matched normocholesterolemic control subjects (58Ϯ4.

Impaired platelet aggregation, normal shape change, and agglutination and normal ATP secretion and thromboxane synthesis in response to high concentrations of thrombin or arachidonic acid were found in a patient with multiple myeloma and hemorrhagic tendency. The purified IgG1 kappa or its F(ab'}2 fragments induced similar changes when added in vitro to plateletrich plasma from normal subjects. In addition, the paraprotein inhibited adhesion to glass microbeads, fibrin clot retraction, and binding of radiolabeled fibrinogen or von Willebrand factor to platelets exposed to thrombin or arachidonic acid without affecting intraplatelet levels of cAMP. The radiolabeled paraprotein bound to an average of 35,000 sites on normal platelets but it bound to <2,000 sites on the platelets from a patient with Glanzmann's thrombasthenia. Immunoprecipitation studies showed that the platelet antigen identified by the paraprotein was the glycoprotein IlIa. Furthermore, binding of radiolabeled prostaglandin El (PGEI) to resting platelets as well as binding of von Willebrand factor to platelets stimulated with ristocetin were entirely normal in the presence of patient's inhibitor. These studies indicate that bleeding occurring in dysproteinemia may be the result of a specific interaction of monoclonal paraproteins with platelets. In addition, our data support the concept that the interaction of fibrinogen and/or von Willebrand factor with the platelet glycoprotein Ilb-IIla complex is essential for effective hemostasis.

Human platelet concentrates stored at 22#{176}C for transfusion purposes progressively lose their in vitro sensitivity to single aggregating agents such as adenosine diphosphate (ADP). It is known that very small amounts of epinephrine. collagen. or arachidonic acid can markedly enhance the aggregation of platelets in fresh platelet-rich plasmas in response to concentrations of ADP that do not cause aggregation when used singly. Therefore. we investigated the effects of pairs of aggregating agents on eight platelet concentrates on the day of preparation and after 3 and 5 days of storage at 22#{176}C. We studied platelet aggregation and secretion with a lumi-aggregometer and thromboxane-B2 formation using a radioimmunoassay. When aggregation was tested in response to single agents. stored platelets were completely unresponsive to epinephrine. markedly insensitive to ADP, and moderately insensitive to collagen and arachidonic acid. In spite of this. there was no statistically significant loss of sensitivity to aggregating agents

We compared the ability of aspirin to suppress platelet aggregation and thromboxane synthesis in ten normal subjects and ten patients with diabetic angiopathy and high rate of entry of new platelets into the circulation. When single doses of 100 to 1,000 mg aspirin were ingested daily for 1 month, there were time gaps between doses in which platelets from diabetics and normals aggregated and formed thromboxane ex vivo in response to the combination of arachidonic acid plus collagen. Similar gaps were also found for diabetics, but not for normals, following four daily doses (every six hours) of 25 or 100 mg. Our data show that dose schedules of aspirin which may suffice in normals are not effective in patients with diabetic angiopathy, presumably because these patients have a high rate of entry of new platelets into the circulation. We suggest that continual suppression of platelet thromboxane synthesis and aggregation by low-dose, “slow- release” preparations of aspirin would be an ideal long-term approach for the prevention of thrombosis in patients with a high rate of entry of new platelets into the circulation.

New containers allow storage of platelet concentrates (PC) at 22 degrees C for up to 7 days, during which glycolytic and oxidative metabolism is vigorous. Recent evidence suggests that 85 percent of adenosine triphosphate regeneration is based on oxidative metabolism and that substrates other than glucose may be used. Because platelets can oxidize free fatty acids (FFA) as a possible source of energy during storage, the authors studied their availability, distribution, and turnover. Plasma FFA concentration was unchanged after 1 day of PC storage but significantly increased on Days 3, 5, and 7. Platelet-free plasma (PFP) stored under the same conditions as PC demonstrated a progressive increase in FFA, suggesting that some of the FFA accumulating in PC were derived from plasma rather than platelets. Indeed, during PC storage, plasma triglycerides decreased significantly, suggesting that they are a possible source of the increased levels of FFA found on Day 3 and thereafter. Thus, PC have a plasma FFA pool available continuously for oxidation during storage. Studies with radiolabeled palmitate suggested that FFA oxidation by platelets occurs during storage. The current findings show that plasma FFA could be a significant substrate for oxidative metabolism during storage of PC and that the oxidized FFA are replenished at least in part from plasma. These results may allow platelet storage to be improved, particularly in synthetic media.