Individually controlled aspirin in the long-term treatment of patients with chronic arterial diseases

Early changes in lipid peroxidation and antioxidative defense in diabetic rat retina: effect of DL-alpha-lipoic acid

This study was designed to (1) evaluate retinal lipid peroxidation in early diabetes by the method specific for free malondialdehyde and 4-hydroxyalkenals, (2) identify impaired antioxidative defense mechanisms and (3) assess if enhanced retinal oxidative stress in diabetes is prevented by the potent antioxidant, DL-alpha-lipoic acid. The groups included control and streptozotocin-diabetic rats treated with or without DL-alpha-lipoic acid (100 mg kg(-1) day(-1), i.p., for 6 weeks). All parameters were measured in individual retinae. 4-Hydroxyalkenal concentration was increased in diabetic rats (2.63+/-0.60 vs. 1.44+/-0.30 nmol/mg soluble protein in controls, P<0.01), and this increase was prevented by DL-alpha-lipoic acid (1.20+/-0.88, P<0.01 vs. untreated diabetic group). Malondialdehyde, reduced glutathione (GSH) and oxidized glutathione (GSSG) concentrations were similar among the groups. Superoxide dismutase, glutathione peroxidase (GSHPx), glutathione reductase (GSSGRed) and glutathione transferase (GSHTrans) activities were decreased in diabetic rats vs. controls. Quinone reductase was upregulated in diabetic rats, whereas catalase and cytoplasmic NADH oxidase activities were unchanged. DL-alpha-Lipoic acid prevented changes in superoxide dismutase and quinone reductase activities induced by diabetes without affecting the enzymes of glutathione metabolism. In conclusion, accumulation of 4-hydroxyalkenals is an early marker of oxidative stress in the diabetic retina. Increased lipid peroxidation occurs in the absence of GSH depletion, and is prevented by DL-alpha-lipoic acid.

Effects of storage on in vitro platelet responses: comparison of ACD and Na citrate anticoagulated samples

The present study was designed to evaluate whether the use of acid citrate dextrose (ACD) Formula A may enhance the survival of platelets during storage, thus allowing the continuance of platelet studies over the period of 2-3 hours usually recommended. For this purpose the effects of time on in vitro platelet response to several agonists have been investigated in platelet-rich plasma (PRP) obtained from blood samples anticoagulated with either Na citrate or ACD Formula A. The analysis of the data obtained in in vitro platelet aggregation studies using various parameters and at different time points demonstrated that storage of PRP obtained from citrated samples caused a marked reduction of platelet responses. This reduction was already evident after 6 hours, and a strong decrease was observed after 8 hours with all the agonists used. On the other hand, storage of ACD anticoagulated blood did not cause any significant decrease of platelet responsiveness up to 6 hours. A reduction of platelet aggregation became evident only after 8 hours, but not to the same extent as the one observed in citrated samples. Therefore, it may be concluded that the use of ACD Formula A as anticoagulant is capable of maintaining a normal platelet responsiveness up to 6-8 hours, thus permitting the investigation of platelet function for periods of time over those commonly recommended.

Acid citrate dextrose (ACD) formula A as a new anticoagulant in the measurement of in vitro platelet aggregation

To evaluate whether the use of ACD Formula A may affect in vitro platelet function, blood samples were obtained from 21 healthy blood donors and anticoagulated in ACD (acid-citrate dextrose, NIH Formula A), Na citrate 3.8%, and K3EDTA. Platelet count, mean platelet volume, and in vitro platelet aggregation were evaluated on each sample. No significant difference was observed in platelet count and mean platelet volume among the different samples. Conversely, the ACD treated platelets showed a higher reactivity to the agonists as demonstrated by a significant increase of the maximum percentages of aggregation induced by ADP, epinephrine, and collagen, as well as a significant decrease of secondary aggregation thresholds to ADP and epinephrine. In conclusion, it may be speculated that ACD Formula A is capable of better maintaining the intraplatelet signal transduction mechanisms during PRP preparation, thus improving the overall responsiveness of platelets.

Influence of various doses of aspirin (in vivo) on platelet arachidonic acid metabolism (ex vivo) and function

The influence of various doses of enteric-coated aspirin was evaluated for its in vivo effect on ex vivo platelet arachidonic acid metabolism and function. 24 h after ingestion of the drugs compromised platelet response to the action of agonists such as epinephrine and arachidonate could be demonstrated with as low a dose as 50 mgs aspirin. However, platelets with compromised function were still capable of producing significant quantities of thromboxane. On the other hand, platelets with almost total inhibition of cyclooxygenase activity were capable of aggregating irreversibly when challenged with epinephrine and arachidonate.

Evaluation of the clinical utility of platelet aggregation studies in the long-term follow-up of patients with atherosclerotic vascular disease

The present study was designed to evaluate the usefulness of laboratory monitoring of antiplatelet therapy by means of a multiparametric evaluation of in vitro platelet aggregation tests in the attempt to individually optimize a given therapeutic regimen. The presence of a condition of hyperaggregability was shown in approximately 80% of patients with different forms of atherosclerotic vascular disease not undergoing any therapeutic regimen with antiplatelet agents. Conversely, a significant decrease in platelet activity was observed in patients undergoing different therapies based on acetylsalicylic acid (ASA), ticlopidine, or indobufen. The similar antiaggregatory effect of low-dose vs. high-dose ASA therapies was also shown. Dipyridamole alone showed no antiaggregatory effect, which, in turn, was reached only by the addition of ASA. Nevertheless, the association of ASA plus dipyridamole did not show any stronger antiplatelet effect than ASA alone. The evaluation of in vitro platelet activity in a group of patients treated with picotamide failed to show any significant change in comparison with the untreated group, probably due to the short half-life of picotamide in man and/or to its capability of reversibly antagonizing the action of thromboxane at receptor level. The evaluation of a long-term follow-up of 90 patients treated with different antiplatelet agents supports the idea that a multiparametric analysis of in vitro platelet aggregation may provide valuable help in monitoring and optimizing a given therapeutic regimen.