Interaction of salicylate and other non-steroidal anti-inflammatory drugs with aspirin on platelet and vascular cyclo-oxygenase activity

Monitoring of reactive oxygen species production after traumatic brain injury in rats with microdialysis and the 4-hydroxybenzoic acid trapping method

The detection of reactive oxygen species (ROS) after traumatic brain injury (TBI) is based on indirect methods due to the high reactivity and short half-life of ROS in biological tissue. The commonly used salicylate trapping method has several disadvantages making it unsuitable for human use. We have evaluated 4-hydroxybenzoic acid (4-HBA) together with microdialysis (MD) in the rat as an alternative method. 4-HBA forms one stable adduct, 3,4-dihydroxybenzoic acid (3,4-DHBA), when reacting with ROS and has not previously been used together with MD after TBI. Twenty-seven rats were used for the assessment of 3,4-DHBA production as an indicator of ROS formation in a controlled contusion injury model using intracerebral MD with 3 mM 4-HBA in the perfusate. For comparison, salicylate trapping was used in eight rats. TBI caused a 250% increase of 3,4-DHBA that peaked at 30 min after injury in severely injured rats and remained significantly elevated as compared to baseline for 90 min after trauma. The mild injury level caused a 100% increase in 3,4-DHBA formation at 30 min after the injury. When the MD probe was placed in the perimeter of the injury site, no significant increase in ROS formation occurred. Salicylate trapping showed a similar increase in adduct formation after severe injury. In addition, high cortical concentrations of 4-HBA and salicylate were found. It is concluded that microdialysis with 4-HBA as a trapping agent appears to be a useful method for ROS detection in the rat with a potential clinical utility.

Differential effect of aspirin on thromboxane and prostaglandin biosynthesis in man

1. Effects of a single intravenous dose of aspirin (600 mg) on bradykinin-stimulated prostaglandin (PG) and on thromboxane (TX) biosynthesis were determined in nine healthy male volunteers. Plasma concentrations of 6-oxo-PGF1 alpha and 13,14-dihydro-15-oxo-PGF2 alpha were measured in samples obtained during repeated 10 min intravenous infusions of bradykinin before and up to 6 h after the dose of aspirin. TXB2 was measured in serum from blood allowed to clot at 37 degrees C. 2. Aspirin inhibited bradykinin stimulated PG and platelet TX biosynthesis 0.5 h after the dose. Serum TXB2 remained low, whereas PG synthesis recovered within 6 h. 3. Effects of intravenous sodium salicylate (600 mg) were studied identically in eight subjects. Prostanoid biosynthesis was not inhibited. 4. Biosynthesis of prostacyclin and TXA2 under basal conditions was studied in eight subjects by measuring 2,3-dinor-6-oxo-PGF1 alpha and 2,3-dinor-TXB2 in hourly urine samples obtained during and after intravenous infusion of aspirin and, on a separate occasion, of vehicle. 5. Aspirin infusion reduced urinary excretion of both metabolites greater than 90%, but excretion of 2,3-dinor-6-oxo-PGF1 alpha recovered more rapidly than did that of 2,3-dinor-TXB2. 6. We conclude that cyclo-oxygenase is rapidly synthesised in bradykinin-responsive tissues in vivo and that this reflects similarly rapid enzyme biosynthesis in tissues that produce PGI2 under basal conditions.

Effects of salicylic and acetylsalicylic acid alone and in combination on platelet aggregation and prostanoid synthesis in man

The present study was designed to investigate the effects of salicylate on the antiplatelet action of acetylsalicylic acid as well as on in vivo prostanoid formation and platelet function in healthy volunteers. In the first study six female volunteers received 350 mg acetylsalicylic acid intravenously, with and without previous oral administration of sodium salicylate (1200 mg daily for 3 days). Urinary prostanoid excretion as well as platelet aggregation and thromboxane formation were measured before and during salicylate and after acetylsalicylic acid. In the second study seven female volunteers received sodium salicylate (52.6 mg kg-1) or acetylsalicylic acid (60.7 mg kg-1) for 8 days in a randomized cross-over protocol. Urinary prostanoid excretion, platelet aggregation and thromboxane formation as well as salicylate plasma concentrations were determined before, during and after administration of each drug. Sodium salicylate did not impair the complete suppression of arachidonic acid-induced platelet thromboxane formation and aggregation obtained by the single intravenous dose of acetylsalicylic acid in the first study. Sodium salicylate in the second study did not affect urinary excretion of prostaglandin E2, its major urinary metabolite (7 alpha-hydroxy-5,11-diketo-tetranor-prostane-1,16-dioic acid), and 2,3-dinor-6-keto-prostaglandin F1 alpha, the main urinary metabolite of epoprostenol (prostacyclin, PGI2). In contrast, acetylsalicylic acid significantly decreased excretion rates of these prostanoids by 64, 59 and 61%, respectively. In both studies platelet aggregation and thromboxane formation induced by collagen, thrombin or arachidonic acid were not significantly affected by salicylate administration, whereas acetylsalicylic acid inhibited platelet aggregation induced by all three agents as well as thrombin- and arachidonic acid induced thromboxane formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Salicylate antagonizes the antiinflammatory action of aspirin in the rat

On the ground of conflicting evidence concerning the interaction of salicylate and aspirin, we investigated the results of such interaction on carrageenin edema of the rat hind paw. Aspirin and sodium salicylate were administered by stomach tube either singly or in combination, at a dose of 50 mg/kg each. The antiinflammatory effect was significantly greater when aspirin was administered prior to salicylate than when aspirin followed salicylate. It is therefore suggested that salicylate may antagonize the action of aspirin in vivo, and that the temporal order in which the two drugs interact with cyclooxygenase may be an important determinant of the outcome.

Plasma salicylate levels and platelet function after acute and chronic administration of slow-release acetylsalicylic acid (Monobeltin)

The relationships between the antiplatelet effects and the pharmacokinetics of a slow release formulation of acetylsalicylic acid (ASA) have been investigated. After acute intake of 750 mg ASA in a slow-release formulation (Monobeltin), a slow increase in plasma ASA was paralleled by a gradual decrease in certain platelet functions. During chronic medication (750 mg twice daily), ASA was present in plasma at all times accompanied by full inhibition of platelet aggregation. For chronic antiplatelet therapy, this slow release formulation of ASA appears to be very effective, unless rapid inhibition of platelet function must be achieved.

Effect of aspirin and salicylate on platelet-vessel wall interactions in rabbits

We performed studies to examine the mechanism responsible for the antithrombogenic effect of aspirin in experimental animals. We measured the effect of 10 and 100 mg/kg doses of aspirin, salicylate, or a combination of both on the accumulation of radiolabeled platelets onto injured carotid arteries in rabbits. The effects of these agents on thrombogenicity measured as platelet accumulation onto injured carotid arteries, were correlated with the ability to inhibit platelet thromboxane A2 and vessel wall prostacyclin synthesis. We found that a low dose of aspirin significantly inhibited platelet accumulation onto the injured vessels, while a high dose reversed this effect. Thromboxane A2 and prostacyclin production, however, were maximally inhibited in rabbits given either aspirin dose. The reversal of the antithrombotic effect of the low dose of aspirin by a high dose of aspirin was simulated by administering a combination dose of high-dose salicylate and low-dose aspirin. We concluded that the reversal of the antithrombotic effect of a 10 mg/kg dose of aspirin by a higher dose of aspirin could not be explained solely by the inhibition of PGI2 synthesis and was affected by the salicylate moiety of aspirin.

Determinants of the pharmacokinetics of antithrombotic drugs

This review describes a variety of factors which determine the pharmacokinetics of antithrombotic drugs, viz., elimination by hepatic and/or renal clearance, plasma protein binding and drug disposition in the geriatric population. An understanding of biotransformation of acetylsalicylic acid and sulfinpyrazone is critical to understanding their usefulness as antithrombotic agents. Acetylsalicylic acid is rapidly hydrolysed to salicylic acid in the body and the latter may be eliminated by five different routes. Two of the biotransformation processes involving salicylic acid are readily saturable. For this reason, salicylate concentration increases more than proportionately with an increase in dose. Acetylsalicylic acid, but not salicylic acid, acetylates cyclo-oxygenase resulting in its inactivation. It is important in pharmacokinetic studies to measure plasma levels of both acetylsalicylic acid and salicylic acid. Biotransformation of sulfinpyrazone involves oxidation to the sulfone and reduction to the sulfide. The sulfide has marked antiplatelet activity. Dipyridamole undergoes hepatic biotransformation to a monoglucuronide which is eliminated by biliary and fecal excretion. Sulfinpyrazone, dipyridamole and salicylic acid are highly bound to plasma proteins. Since binding diminishes with age, one must expect therapeutic and toxic effects at lower plasma drug concentrations in the geriatric population. Other factors to be considered in the geriatric group are altered distribution, diminished glomerular filtration rate, and diminished oxidative biotransformation.