Dose-related kinetics of aspirin. Presystemic acetylation of platelet cyclooxygenase

Inhibition of ADP-evoked platelet aggregation by selected poly(ADP-ribose) polymerase inhibitors

Pathologic platelet activation has been implicated in the pathogenesis of ischemic heart disease. Since cardiomyocytes can be protected from ischemia-reoxygenation injury by poly(ADP-ribose) polymerase (PARP) inhibitors mimicking the adenine/ADP part of NAD, their structural resemblance to ADP may also enable the blockade of platelet aggregation via binding to ADP receptors. Blood samples drawn from healthy volunteers were pre-incubated with different concentrations of PARP inhibitors: 4-hydroxyquinazoline, 2-mercapto-4(3 H)-quinazolinone, or HO-3089. ADP-, collagen- and epinephrine-induced platelet aggregation was evaluated according to the method described by Born. The effect of PARP inhibitors on thrombocyte aggregation was also examined when platelets were sensitized by heparin and in the presence of incremental concentrations of ADP. All examined PARP inhibitors reduced the ADP-induced platelet aggregation in a dose-dependent manner (significant inhibition at 20 microM for HO-3089 and at 500 microM for the other agents; P < 0.05), even if platelets were sensitized with heparin. However, their hindrance on platelet aggregation waned as the concentration of ADP rose (no effect at 40 microM ADP). PARP inhibitors had minimal effect on both collagen- and epinephrine-induced platelet aggregation. Our study first demonstrates the feasibility of a design for PARP inhibitors that does not only protect against ischemia-reperfusion-induced cardiac damage but may also prevent thrombotic events.

Pharmacokinetic and pharmacodynamic differences between two low dosages of aspirin may affect therapeutic outcomes

BACKGROUND

Meta-analyses of the prevention of major vascular events by aspirin suggest therapeutic equivalence of all dosages. However, the optimal dosage still remains problematic, and a recent trial found aspirin 160 mg/day to be more effective than 80 mg/day for secondary prevention of ischaemic stroke.

OBJECTIVE

To evaluate two low dosages of aspirin in terms of pharmacokinetics and pharmacodynamics (inhibition of platelet thromboxane generation and urinary excretion of thromboxane and prostacyclin metabolites).

DESIGN AND PARTICIPANTS

A randomised cross-over study was performed in 16 healthy volunteers (9 women and 7 men, 33.8 +/- 5.1 years old) given enteric-coated aspirin 80 or 160 mg/day for 7 days.

METHODS

Plasma concentrations of salicylate and aspirin were measured by high-performance liquid chromatography (HPLC) after both the first and the last dose (days 1 and 7). The usual pharmacokinetic parameters were then derived. Serum thromboxane B2 (TxB2) was measured by radioimmunoassay. The urinary excretion of 11-dehydro-TxB2 and 2,3-dinor-6-keto-prostaglandin F1alpha were measured on 8-hour urine samples by immunoassay after extraction and HPLC separation, both before and after 7 days of drug administration.

RESULTS

With the 160 mg dosage, but not with the 80 mg dosage, higher concentrations of aspirin were found at day 7 compared with day 1. For aspirin 80 mg/day, 24-hour area under the concentration-time curve (AUC24) was similar on days 1 and 7 (569 +/- 339 vs 605 +/- 377 microg. h/L), but increased from 904 +/- 356 microg. h/L on day 1 to 1355 +/- 883 microg. h/L on day 7 with the higher dosage. Similarly, the AUC24 for salicylate was similar on days 1 and 7 with the lower dosage, but significantly increased from day 1 to day 7 after the higher dosage. This paralleled inhibition of serum TxB2 levels (99% vs 95% average inhibition by 160 and 80 mg/day) and of urinary excretion of thromboxane metabolite (77% vs 61% average inhibition by 160 and 80 mg/day), without altering the excretion of prostacyclin metabolite.

CONCLUSIONS

Inhibition of serum TxB2 generation and of thromboxane metabolite urinary excretion by the lower dosage of aspirin, although substantial, still appeared incomplete. The small but significant further increase of serum TxB2 inhibition by the higher dosage was accompanied by an even greater inhibition of urinary excretion. We suggest that in some instances this difference would translate into a greater clinical benefit with the higher aspirin dosage. Our findings may also contribute to better definition of the recent concept of 'aspirin resistance'.

Acetylsalicylic Acid Inhibits Monocyte Adhesion to Endothelial Cells by an Antioxidative Mechanism

The adhesion of monocytes to vascular endothelium increases in the presence of high levels of low density lipoprotein (LDL). LDL changes oxidative status of endothelial cells leading to an increased expression of cell adhesion molecules. Acetylsalicylic acid (ASA) has been shown to exert antioxidant effects in high and very high concentrations. This study was designed to demonstrate the influence of acetylsalicylic acid and its major metabolite, salicylic acid (SA), on the adhesion of monocytes to LDL-stimulated endothelial cells. Monocyte adhesion to endothelial cells was concentration-dependently inhibited by both salicylates upon stimulation of endothelial cells with TNF-alpha, oxidized LDL (oxLDL), and native LDL (nLDL). The inhibitory effect of ASA was more potent than that of SA, whereas the cyclooxygenase inhibitor ibuprofen had no effect. F2-isoprostane release from LDL-stimulated endothelial cells was reduced by simultaneous incubation with ASA or SA, whereas ibuprofen had no effect. LDL-induced activation of the transcription factor NF-kappaB was inhibited by ASA, and ferritin protein was increased when endothelial cells were incubated with this drug. These results show that acetylsalicylic acid and-less potently-salicylic acid inhibit monocyte adhesion to LDL-stimulated endothelial cells by antioxidative effects. For ASA, the observed inhibition of monocyte adhesion was accomplished with concentrations that can be reached after single oral doses of 500 mg of ASA.

Early and late effects of low-dose aspirin on renal function in elderly patients

BACKGROUND

Although low-dose aspirin is used by many elderly patients, monitoring of renal function is currently not recommended. We recently reported transient retention of uric acid and creatinine caused by aspirin in doses of 75 to 325 mg/d. We therefore evaluated the renal effects of aspirin (100 mg/d), including post-treatment effects.

METHODS

We studied 83 stable geriatric patients in long-term care (aged 56 to 98 years) who were treated with low-dose aspirin (100 mg/d) for 2 weeks and 40 control patients. Other medications and diet were kept constant. Biochemical monitoring including blood samples and 24-hour urinary collections for creatinine and uric acid at baseline and weekly for a total of 5 weeks.

RESULTS

After 2 weeks on aspirin, urinary excretion of creatinine decreased in 60 (72%) and excretion of uric acid decreased in 54 (65%) of the 83 patients, and their mean clearances decreased; during the same period, serum blood urea nitrogen, creatinine, and uric acid levels increased (P <0.05 for all). Deterioration from baseline levels was significantly greater (and more prevalent) in the aspirin-treated group than in the 40 control patients (P = 0.001 to 0.09). After withdrawal of aspirin these parameters improved. However, 3 weeks after stopping aspirin, 48% (35 of the 73 in whom this measurement was available) had a persistent decline in creatinine clearance from baseline, as compared with only 8% (3/36) controls (P <0.001).

CONCLUSION

Short-term low-dose aspirin treatment may affect renal function in elderly patients. These effects persist 3 weeks after cessation of the drug in some of these patients.

Effect of different aspirin doses on platelet aggregation in patients with stable coronary artery disease

BACKGROUND

Aspirin is widely used as an antiplatelet agent in the primary and secondary prevention of cardiovascular disease. In order to spare prostacyclin formation and reduce gastrointestinal side-effects, very low doses of aspirin have been introduced. However, it remains unclear whether these low doses are equally effective with respect to inhibition of platelet aggregation.

AIMS

In a randomized, controlled study in 60 patients with stable coronary artery disease, the effects on platelet aggregation of five doses (50, 80, 100, 162.5 and 325 mg) of aspirin, which are widely used in clinical practice, given for 70 days, were investigated. Two reagents, adenosine diphosphate (ADP) and epinephrine, were used to induce platelet aggregation in platelet-rich plasma. An age- and sex-matched group of people without coronary artery disease served as the control.

RESULTS

ADP- and epinephrine-induced platelet aggregation was 78.2 +/- 12.8% and 76.7 +/- 15.5% of maximum aggregation in the control group. Aspirin inhibited platelet aggregation in a dose-dependent manner. Minimum platelet aggregation was observed at a dose of 325 mg aspirin (27.5 +/- 17.4% with ADP). Doses of 50 and 80 mg aspirin were much less effective in inhibiting platelet aggregation (59.1 +/- 11.4% and 50.3 +/- 12.1% with ADP, respectively). Doses of 100 and 162.5 mg aspirin produced significantly greater inhibition of platelet aggregation than lower doses (36.2 +/- 11.7% and 38.5 +/- 19.8% platelet aggregation with ADP, respectively).

CONCLUSION

Our results demonstrate that doses of aspirin less than 100 mg are not as effective at inhibiting platelet aggregation as doses greater than 100 mg.

Obesity is associated with impaired platelet-inhibitory effect of acetylsalicylic acid in nondiabetic subjects

OBJECTIVE

Platelet aggregation responses to acetylsalicylic acid (ASA) show considerable interindividual variation, the causes of which are largely unknown. We determined whether variation in insulin action is associated with that of ASA on platelets.

SUBJECTS

In all, 10 nonobese (age 50+/-3 y, BMI 25+/-1 kg/m(2)) and 11 obese (age 52+/-2 y, BMI 32+/-1 kg/m(2)) subjects.

MEASUREMENTS

Insulin sensitivity of glucose uptake was determined by the euglycemic insulin clamp technique. Platelet aggregation responses to four doses of arachidonic acid (AA) and adenosine diphosphate (ADP) were assessed in platelet-rich plasma before and 1 h after ingestion of 50 mg ASA using Born's turbidometric aggregometer.

RESULTS

Whole-body insulin sensitivity (M-value 0-180 min) was 36% lower in the obese (4.5+/-0.6) than the nonobese (7.1+/-0.6 mg/kg min, P<0.01) group. Before ASA, all doses of AA induced complete aggregation. After ASA ingestion, ASA inhibited maximal aggregation more in the nonobese than the obese group at AA concentrations of 0.75, 1 and 1.5 mmol/l (P=0.016 for ANOVA). ADP-induced aggregation at high doses (2 and 3 micromol/l) was also less inhibited in the obese group. In vivo insulin sensitivity (r=-0.68, P<0.001 for 1 mmol/l AA) and BMI (r=0.58, P<0.01 for 1 mmol/l AA) were closely correlated with residual aggregation after ASA administration.

CONCLUSION

These data demonstrate that obese insulin-resistant subjects have a blunted response to platelet-inhibitory effect of ASA. If this blunted effect is of a single dose of ASA preserved in continuous use, it could contribute to the increased risk of atherothrombosis in insulin-resistant individuals.

Role of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitors, angiotensin-converting enzyme inhibitors, cyclooxygenase-2 inhibitors, and aspirin in anti-inflammatory and immunomodulatory treatment of cardiovascular diseases

The immunologic response in atherosclerosis involves not only intrinsic cells of the artery wall, but also circulating leukocytes, lymphocytes, and macrophages. Interaction of various arms of the immune response modulates plaque development and stability, and it is conceivable that immunologic effects of some cardiovascular therapies may contribute to their mechanism of benefit. The preponderance of data has accrued with the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins). Statin effects, such as inhibition of T cell activation, tissue factor expression, or reduction of platelet hyperreactivity, may elicit beneficial effects in vitro and in vivo in patients with coronary artery disease. Moreover, aspirin may limit oxidation of lipoproteins and fibrinogen, and it may inhibit cytokine-induced nitric oxide synthase II expression. The hypothesis that selective inhibition of cyclooxygenase-2 (COX-2) may increase risk of myocardial infarction is controversial and may also be of questionable clinical significance. Finally, angiotensin-converting enzyme (ACE) inhibitors not only reduce proinflammatory mediators, such as interleukin-6, but also enhance the concentration of anti-inflammatory cytokines, such as interleukin-10. Because ACE is expressed at the shoulder region of atherosclerotic plaques, and ACE activity is enhanced in unstable plaques, ACE inhibition may also contribute to plaque stability. This article reviews the potential immunomodulatory potencies of aspirin, COX-2 inhibitors, statins, and ACE inhibitors as established pharmacotherapy in patients with coronary artery disease.

Differences in the effects of extended-release aspirin and plain-formulated aspirin on prostanoids and nitric oxide in healthy volunteers

This study was designed to evaluate the effects of extended-release aspirin on platelet aggregation and the production of prostanoids and nitric oxide. The participants in this double blind, randomized and crossover study were 20 healthy volunteers. Interventions were 150 mg of plain-formulated aspirin (PFASA) and 150 mg of extended-release aspirin (ERASA). Blood samples were collected before and 10, 20, 60, 120, 240, 480 and 1440 min after the first dose; 3, 7 and 14 days after daily administration and 24 h after the last dose. The main measures were platelet aggregometry, thromboxane B2, 6-keto-prostaglandin (PG) F1alpha and nitric oxide in each control. Platelet aggregation was inhibited by 50% with ERASA, and by 77% with PFASA. No differences were found in chronic treatment. Thromboxane B2 was inhibited more by the latter (51-67%), but 90% inhibition was observed in both groups after 3 days. The levels of 6-keto-PGF1alpha was reduced by 20% with ERASA and by 58% with PFASA. Nitric oxide production increased in both groups, but after 24 h, and 7-14 days, elevated concentrations of nitric oxide were found only in the ERASA. The antiplatelet effects of ERASA provide pharmacological advantages (greater prostacyclin synthesis and prolonged increase in nitric oxide production) over those provided by the plain formulation.

[Administration-time dependent effects of acetyl-salicylic acid on blood pressure in patients with mild essential hypertension]

BACKGROUND AND OBJECTIVES

Previous studies on the potential influence of aspirin (AAS) on blood pressure have not taken in consideration the chronopharmacologic effects of non-steroidal antiinflammatory drugs. This pilot study investigated the effects of AAS on blood pressure in hypertensive patients under no antihypertensive treatment who received AAS at different day times according to their rest-activity cycle.

PATIENTS AND METHOD

We studied 64 untreated patients with mild hypertension (24 men), 43.5 (12.0) (mean [SD]) years of age, randomly divided in 3 groups: group 1, non-pharmacological hygienic-dietetic recommendations; group 2, the same recommendations plus AAS (100 mg/day) on awakening, and group 3, the same recommendations plus AAS (100 mg/day) before bedtime. Blood pressure was measured every 20 min during the day and every 30 min at night for 48 consecutive hours before and after 3 months of intervention. The circadian pattern of blood pressure in each group was established by population multiple-component analysis. Circadian parameters obtained for each group of patients before and after the intervention were compared with a nonparametric paired test.

RESULTS

After 3 months of non-pharmacological intervention, there was a small and non-significant reduction of blood pressure (< 1.5 mmHg; p = 0.28). There was no change in blood pressure when AAS was given on awakening (p = 0.21). A highly significant blood pressure reduction was, however, observed in patients who received AAS before bedtime (decrease of 7 and 5 mmHg in systolic and diastolic blood pressure, respectively; p = 0.006).

CONCLUSIONS

Our results indicate a statistically significant time-dependent administration effect of low-dose AAS on blood pressure in untreated patients with mild hypertension. This effect reinforces the need to quantify and control AAS effects in patients using this agent in combination with antihypertensive agents.

Aspirin (100 mg) used for prevention of pre-eclampsia in nulliparous women: the Essai Régional Aspirine Mère-Enfant study (Part 1)

OBJECTIVE

To reduce the incidence of pre-eclampsia in nulliparous women, in accordance with the suggestion of a recent meta-analysis that low dose aspirin might decrease this incidence by more than half if used early enough in and at a sufficient dose during pregnancy (more than 75 mg).

DESIGN

Multicentre randomised double-blinded placebo-controlled trial.

SETTING

Twenty eight centres in Northern of France and one in Belgium.

POPULATION

Three thousand and two hundred ninety-four nulliparous women recruited between 14 and 20 weeks.

METHODS

Randomisation to either 100 mg aspirin or placebo daily from inclusion through 34 weeks.

MAIN OUTCOME MEASURES

Preeclampsia was defined as hypertension (> or =140 and or 90 mmHg) associated with proteinuria (> or =0.5 g/L).

RESULTS

The aspirin (n = 1644) and placebo (n = 1650) groups did not differ significantly in the mothers' incidence of pre-eclampsia (28 of 1632 [1.7%] vs 26 of 1637 [1.6%]; relative risk, RR, 1.08, 95% CI 0.64-1.83), hypertension, HELLP syndrome or placental abruption, or in the children's incidence of perinatal deaths or birthweight below the 10th centile. The incidence of babies with birthweight below the third centile was significantly higher in the aspirin group, with no explanation. The incidence of maternal side effects was higher in the aspirin group, principally because of a significantly higher rate of haemorrhage.

CONCLUSIONS

Aspirin at a dose of 100 mg does not reduce the incidence of pre-eclampsia in nulliparous women. Aspirin (100 mg) is associated with an increase in bleeding complications.

The ingestion of inorganic nitrate increases gastric S-nitrosothiol levels and inhibits platelet function in humans

Platelets play an important role in the development of vascular disease, while vegetarian diets, which are rich in inorganic nitrate, protect against it. This study was performed to assess the effect of potassium nitrate (KNO(3)) ingestion on platelet function in humans. Oral KNO(3) (2 mmol) was given to healthy volunteers and its effect on platelet function assessed by measuring the aggregant effect of collagen. Blood samples were taken for measurement of plasma S-nitrosothiols (RSNO) and platelet cyclic GMP and nitrotyrosine levels. Gastric juice samples were taken for measurement of RSNO. In a separate study, the effect of oral KNO(3) on portal RSNO levels in patients with intrahepatic porto-systemic shunts was assessed. KNO(3) caused a significant increase in gastric RSNO levels, from 0.46 +/- 0.06 to 3.62 +/- 2.82 microM (t(max) 45 min; P < 0.001), and significantly inhibited platelet function (t(max) 60 min; P < 0.001). There was no effect on systemic or portal RSNO, platelet cGMP or platelet nitrotyrosine levels. Oral KNO(3) inhibits platelet aggregation. The time course suggests that gastric RSNO production may be involved in this effect. The protection against vascular events associated with a high intake of vegetables may be due to their high nitrate content.

Is aspirin "the weakest link" in cardiovascular prophylaxis? The surprising lack of evidence supporting the use of aspirin for cardiovascular disease

It is currently fashionable to prescribe aspirin, long-term to people with or at high risk of vascular events due to atherosclerosis. There is a moderately conclusive evidence for a short-term benefit after an acute vascular event. However, there is remarkably little evidence that long-term aspirin is effective for the prevention of vascular events and managing side effects may be expensive. Reductions in nonfatal vascular events may reflect an ability of aspirin to alter cosmetically the presentation of disease without exerting real benefit. Cardiovascular medicine appears prone to fads and fashions that are poorly substantiated by evidence. The current fashion for prescribing aspirin is reminiscent of the now discredited practice of widespread prescription of class I anti-arrhythmic drugs for ventricular ectopics. We should learn from experience.

Cyclooxygenase inhibitors and the antiplatelet effects of aspirin

BACKGROUND

Patients with arthritis and vascular disease may receive both low-dose aspirin and other nonsteroidal antiinflammatory drugs. We therefore investigated potential interactions between aspirin and commonly prescribed arthritis therapies

METHODS

We administered the following combinations of drugs for six days: aspirin (81 mg every morning) two hours before ibuprofen (400 mg every morning) and the same medications in the reverse order; aspirin two hours before acetaminophen (1000 mg every morning) and the same medications in the reverse order; aspirin two hours before the cyclooxygenase-2 inhibitor rofecoxib (25 mg every morning) and the same medications in the reverse order; enteric-coated aspirin two hours before ibuprofen (400 mg three times a day); and enteric-coated aspirin two hours before delayed-release diclofenac (75 mg twice daily)

RESULTS

Serum thromboxane B(2) levels (an index of cyclooxygenase-1 activity in platelets) and platelet aggregation were maximally inhibited 24 hours after the administration of aspirin on day 6 in the subjects who took aspirin before a single daily dose of any other drug, as well as in those who took rofecoxib or acetaminophen before taking aspirin. In contrast, inhibition of serum thromboxane B(2) formation and platelet aggregation by aspirin was blocked when a single daily dose of ibuprofen was given before aspirin, as well as when multiple daily doses of ibuprofen were given. The concomitant administration of rofecoxib, acetaminophen, or diclofenac did not affect the pharmacodynamics of aspirin

CONCLUSIONS

The concomitant administration of ibuprofen but not rofecoxib, acetaminophen, or diclofenac antagonizes the irreversible platelet inhibition induced by aspirin. Treatment with ibuprofen in patients with increased cardiovascular risk may limit the cardioprotective effects of aspirin.

A high level of cyclooxygenase-2 inhibitor selectivity is associated with a reduced interference of platelet cyclooxygenase-1 inactivation by aspirin

Both nonsteroidal anti-inflammatory drugs, such as ibuprofen, and the prototypical selective cyclooxygenase (Cox)-2 inhibitors DuP-697 and NS-398 block the inhibition of Cox-1 by aspirin in vitro. However, clinical studies have shown that the Cox-2 selective drugs (or coxibs) rofecoxib and etoricoxib, at therapeutic doses, do not interfere with the antiplatelet effect of aspirin, in contrast to ibuprofen. Here, we have evaluated the relative potential of ibuprofen and various coxibs to interfere with the inactivation of Cox-1 by aspirin by using purified enzyme and calcium ionophore-activated human platelets. The irreversible inactivation of Cox-1 by aspirin can be antagonized by ibuprofen and coxibs, albeit with widely different potencies. The rank order of potencies for this process (ibuprofen > celecoxib > valdecoxib > rofecoxib > etoricoxib) parallels that obtained for the inhibition of Cox-1-mediated thromboxane B(2) production by calcium ionophore-stimulated platelets. The antagonism of aspirin therefore likely involves a competition at the enzyme active site. The EC(50) value for the antagonism against 10 microM aspirin for each drug is approximately 10- to 40-fold lower than the corresponding IC(50) value for inhibition of platelet Cox-1 activity, consistent with the much weaker initial binding of aspirin to Cox-1 as compared with arachidonic acid. These results show that a low affinity for Cox-1 and a high degree of Cox-2 selectivity confers a low potential to block aspirin inhibition of platelet Cox-1, consistent with the results of clinical studies.

Pharmacological control of platelet function

Advancement in the understanding of the mechanisms of platelet activation, as well as the development of new techniques for studying platelet function, have led to the availability of new classes of platelet inhibiting drugs. Initially, characterization of arachidonic acid metabolism in platelets furthered an understanding of the utility of cyclooxygenase inhibitors, most notably aspirin. The discovery and characterization of platelet receptors such as the adenosine diphosphate (ADP) receptor and glycoprotein IIb/IIIa has been associated with the development of novel classes of anti-platelet drug, such as thienopyridine derivatives and glycoprotein IIb/IIIa receptor antagonists, respectively. Future development in receptor pathway inhibitors also includes glycoprotein Ib/IX as well as the potential use of platelet signaling pathway inhibitors.

Antiplatelet therapy in the elderly. Aspirin, ticlopidine-clopidogrel, and GPIIb/GPIIIa antagonists

Antiplatelet agents including aspirin, dipyridamole, the thienopyridines, and the GPIIb/IIIa antagonists have collectively demonstrated their ability to have a significant impact on the incidence of recurrent MIs, strokes, and other vascular ischemic events in the geriatric population. Low-dose aspirin also seems to be effective and safe for the primary prevention of ischemic heart disease in men considered at high risk. There is no evidence that the recommendations from these studies had increased relevance to younger adults, and the studies considering age as a variable found antiplatelet agents had either similar or increased benefit in older patients. In view of the relatively reduced adverse effects of these agents when compared with their potential therapeutic benefit, it is important that they be considered in all older patients for secondary prevention and in certain high-risk groups for primary prevention of cardiovascular morbidity and mortality.

Endogenous biosynthesis of thromboxane and prostacyclin in 2 distinct murine models of atherosclerosis

Thromboxane A2 is a potent vasoconstrictor and platelet agonist; prostacyclin is a potent platelet inhibitor and vasodilator. Altered biosynthesis of these eicosanoids is a feature of human hypercholesterolemia and atherosclerosis. This study examined whether in 2 murine models of atherosclerosis their levels are increased and correlated with the evolution of the disease. Urinary 2,3-dinor thromboxane B2 and 2,3-dinor-6-keto prostaglandin F1α, metabolites of thromboxane and prostacyclin, respectively, were assayed in apoliprotein E (apoE)-deficient mice on chow and low-density lipoprotein receptor (LDLR)-deficient mice on chow and a Western-type diet. Atherosclerosis lesion area was measured by en face method. Both eicosanoids increased in apoE-deficient mice on chow and in LDLR-deficient mice on a high-fat diet, but not in LDLR-deficient mice on chow by the end of the study. Aspirin suppressed ex vivo platelet aggregation, serum thromboxane B2, and 2,3-dinor thromboxane B2, and significantly reduced the excretion of 2,3-dinor-6-keto prostaglandin F1α in these animals. This study demonstrates that thromboxane as well as prostacyclin biosynthesis is increased in 2 murine models of atherogenesis and is secondary to increased in vivo platelet activation. Assessment of their generation in these models may afford the basis for future studies on the functional role of these eicosanoids in the evolution and progression of atherosclerosis.

Endogenous biosynthesis of thromboxane and prostacyclin in 2 distinct murine models of atherosclerosis

Thromboxane A2 is a potent vasoconstrictor and platelet agonist; prostacyclin is a potent platelet inhibitor and vasodilator. Altered biosynthesis of these eicosanoids is a feature of human hypercholesterolemia and atherosclerosis. This study examined whether in 2 murine models of atherosclerosis their levels are increased and correlated with the evolution of the disease. Urinary 2,3-dinor thromboxane B2 and 2,3-dinor-6-keto prostaglandin F1α, metabolites of thromboxane and prostacyclin, respectively, were assayed in apoliprotein E (apoE)-deficient mice on chow and low-density lipoprotein receptor (LDLR)-deficient mice on chow and a Western-type diet. Atherosclerosis lesion area was measured by en face method. Both eicosanoids increased in apoE-deficient mice on chow and in LDLR-deficient mice on a high-fat diet, but not in LDLR-deficient mice on chow by the end of the study. Aspirin suppressed ex vivo platelet aggregation, serum thromboxane B2, and 2,3-dinor thromboxane B2, and significantly reduced the excretion of 2,3-dinor-6-keto prostaglandin F1α in these animals. This study demonstrates that thromboxane as well as prostacyclin biosynthesis is increased in 2 murine models of atherogenesis and is secondary to increased in vivo platelet activation. Assessment of their generation in these models may afford the basis for future studies on the functional role of these eicosanoids in the evolution and progression of atherosclerosis.

Time related neutralization of two doses acetyl salicylic acid

Aspirin has a well established role in the prevention of arterial thrombosis. Discussion on the efficacy and safety of aspirin in the treatment and prophylaxis of thrombosis has become an important issue. In fact, hemorrhage complications are often associated with its use. On the other hand, previous studies showed unexpected thrombotic potencies associated with the presence of this drug at ultra low doses (ULD) in the circulation. In this study, we aimed to evaluate the effect of aspirin at ULD, injected 1, 2, or 3 hours after the administration of aspirin at 100 mg/kg, on hemostasis and bleeding in rats. We used an experimental model of thrombosis induced by laser beams to evaluate these effects. Platelet aggregation was determined by Cardinal and Flower method. Results from this investigation demonstrate that the neutralizing effect of aspirin at ULD did not operate significantly 1 hour after the injection of aspirin at 100 mg/kg. This effect was observed 2 and 3 hours after. The use of aspirin at ULD to neutralize the side effects of aspirin at high doses will reduce the hemorrhagic risk during extra corporeal circulation. The therapeutic benefit and safety of aspirin therapy in the treatment of cardiovascular diseases can be obtained.

Effects of acetyl salicylic acid therapy on an experimental thrombosis induced by laser beam

Aspirin inhibits the synthesis of both platelet and vascular arachidonic acid metabolism which have opposite effects on platelet functions. The rationale for its clinical use as an antithrombotic drug has therefore been questioned. Therefore, we investigated the effects of acetylsalicylic acid (ASA) at 100 mg/kg on an experimental thrombosis induced by laser beams using different groups of rats that were previously treated with the same dose (100 mg/kg), according to the delay between the first and second injections. A partial occlusion was induced by laser beams in the rat mesenteric microvessels (15-25 m). The thrombus formed within seconds after the laser lesion; both it and the embolization which began within minutes after, were continuously accounted. Experiments were done on 11 groups of 5 animals each: 45 rats received a first injection of ASA at j(0) and a second injection 30 minutes before thrombosis induction at j(0)+x (x=2, 4, 6, 8, 9, 10, 12, 14 and 16 days). Different groups are defined according to the x value. The rats receiving NaCl 0.9% or a single injection of ASA at 100 mg/kg 30 minutes before thrombosis induction were used as control (Group I) and reference group (Group II) respectively. In this study, ASA treatment showed two types of results. The administration of ASA (100 mg/kg) 30 minutes before laser-induced thrombosis prevented thrombus formation. In the same way, ASA injected to rats already treated with the same dose 2 or 4 day later also demonstrated a potent antithrombotic effect. The same trends were observed with animals receiving the second injection (100 mg ASA) at j(0+8), j(0+12), j(0+14), and j(0+16). However, when injected to rats at j(0+6) and at j(0+10), ASA did not shown any effects on thrombus formation compared to the control (p>/=0.05). The same phases of ASA action were observed on the induced hemorrhagic time. The antithrombotic effects of the later second injection of ASA (100 mg/kg) were neutralized in rats previously receiving the same dose of this drug. This phenomenon seems to be periodic and is of great importance for the observance of ASA treatment.

Over-the-counter analgesics and antipyretics: a critical assessment

BACKGROUND

It is just 100 years since the introduction of aspirin to medicine. Since then, aspirin and its derivatives have been joined by acetaminophen, and the nonsteroidal anti-inflammatory drugs--ibuprofen, naproxen sodium, and ketoprofen--as the only over-the-counter (OTC) agents approved by the US Food and Drug Administration for the short-term treatment of pain, headache, dysmenorrhea, and fever. Recently the prescription use of aspirin has expanded to include a number of antiplatelet indications.

OBJECTIVE

The purpose of this paper is to review critically the history, mechanisms of action, efficacy, and tolerability of OTC analgesic and antipyretic products. Relatively new and potential future indications for these drugs are also discussed.

CONCLUSION

Although all of the OTC analgesic/antipyretic agents seem to share a common mechanism of prostaglandin inhibition, there are important differences in their pharmacology, efficacy, and side-effect profiles. Considering their often-unsupervised use, the risk-benefit ratio of this class of drugs has been extremely favorable. However, when used inappropriately, even these drugs pose significant risks to certain patient populations.

Omeprazole does not interfere with the antiplatelet effect of low-dose aspirin in man

BACKGROUND

Experimental studies have shown that omeprazole and other anti-inflammatory agents compromise the therapeutic activity of nonsteroidal anti-inflammatory drugs and aspirin in rats. It is not known whether this effect will occur in humans. Our aim was to determine whether omeprazole affects the antiplatelet effects of low-dose aspirin in humans.

METHODS

Platelet lumiaggregation, skin bleeding time, plasma levels of aspirin and salicylic acid, and serum gastrin levels were determined in 14 healthy men before and after the ingestion of 125 mg aspirin with or without previous treatment with 20 mg/day of omeprazole for 4 days before testing.

RESULTS

Omeprazole increased serum gastrin levels from 64 (median; range, 52-91) pg/ml to 80.5 (median; range, 56-455) pg/ml (P < 0.05) but did not significantly affect the plasma concentration of aspirin or salicylic acid. Aspirin increased skin bleeding time in all subjects, and the increase was similar with and without previous omeprazole treatment. Aspirin inhibited platelet aggregation in response to both collagen and arachidonic acid regardless of omeprazole treatment.

CONCLUSION

A single dose of 20 mg omeprazole daily does not interfere with the biologic activity of 125 mg aspirin on platelets in humans.

Antiplatelet and antithrombotic effects of a novel selective phosphodiesterase 3 inhibitor, NSP-513, in mice and rats

We investigated the effects of NSP-513, (R)-4,5-dihydro-5-methyl-6-[4-(2-propyl-3-oxo-1-cyclohexenyl)amino] phenyl-3(2H)-pyridazinone, on phosphodiesterase (PDE) isozyme activities, in vitro platelet aggregation and in vivo thrombus formation. NSP-513 selectively inhibited human platelet PDE 3 isozyme with an IC50 value of 0.039 microM. In an in vitro human platelet aggregation assay, the IC50 values (microM) of NSP-513 for platelet aggregation induced by collagen, U-46619, arachidonic acid, adenosine diphosphate (ADP), epinephrine and thrombin were 0.31, 0.25, 0.082, 0.66, 0.23 and 0.73, respectively. In a mouse pulmonary thromboembolism model, orally administered NSP-513 showed in vivo antithrombotic effects that were 320 to 470 times more potent than those of cilostazol. In a rat carotid arterial thrombosis model, intraduodenally administered NSP-513 (0.1 mg/kg), cilostazol (30 mg/kg) and aspirin (30 mg/kg) reduced thrombus formation by 75%, 66% and 48%, respectively. However, intravenously administered dipyridamole (10 mg/kg) did not significantly prevent thrombus formation. These results demonstrate that NSP-513 has the potential to prevent not only in vitro platelet aggregation but also in vivo thrombus formation and indicate that the highly selective PDE 3 inhibitory effect of NSP-513 may make this compound useful for assessing the physiological role of PDE 3.

Prospective Comparison of Patient Characteristics and Outcome of Non-prior Aspirin Users versus Aspirin Users with Unstable Angina or Non-Q-Wave Myocardial Infarction Treated with Combination Antithrombotic Therapy

The objective of this study was to determine if aspirin users presenting with acute coronary syndromes are at higher risk for subsequent clinical events. In a trial evaluating combination antithrombotic therapy in resting angina or non-Q-wave myocardial infarction (MI), patients were prospectively dichotomized on admission into nonprior versus recent aspirin users. Then 105 nonprior users and 144 users were randomized to treatment with aspirin plus heparin/warfarin for 12 weeks. Recurrent myocardial ischemia occurring during the 12-week follow-up period was defined as recurrent angina (with electrocardiographic changes or prompting coronary revascularization), MI, or death. Prior aspirin users had a significantly higher incidence of previous MI, prior bypass grafting, beta-blocker use, or hypertension (p </= 0.003) and were more likely to present with unstable angina as opposed to non-Q-wave MI. (p </= 0.008). The cumulative probability of recurrent ischemic endpoints for nonprior versus recent users was 10% versus 21% at 14 days (log rank p = 0.03), and 19% versus 29%, at 12 weeks (p = 0.06). Using the Cox model, adjusting for variables significantly associated with outcome, aspirin use remained a significant predictor of 14-day outcome (p = 0.04) but not of 12-week outcome (p = 0.06). In conclusion, even after adjusting for significant differences in baseline variables, aspirin users presenting with rest angina or non-Q-infarction have a worse short-term prognosis in spite of maximal medical therapy.

The effect of mini-dose aspirin on renal function and uric acid handling in elderly patients

OBJECTIVE

Aspirin is known to have a bimodal effect on the renal handling of uric acid (UA). High dosages (>3 gm/day) are uricosuric, while low dosages (1-2 gm/day) cause UA retention. Although very-low-dose (mini-dose) aspirin is used increasingly as a platelet aggregation inhibitor, no studies have been published on whether aspirin's renal effects occur at dosages of <0.5 gm/day. The aim of the present study was to evaluate the effects of commonly used mini-dosages of aspirin on renal function and UA handling in elderly patients.

METHODS

The study included 49 elderly inpatients (age 61-94). Patients were excluded if they had renal failure, hyperuricemia, gout, or a history of bleeding, or if they were receiving anticoagulants, aspirin, or nonsteroidal antiinflammatory drugs. Previous medications and diet were kept unchanged. Aspirin was administered as follows: 75 mg/day (week 1), 150 mg/day (week 2), 325 mg/day (week 3), and 0 mg/day (week 4). Baseline and weekly samples of blood and urine were evaluated for UA, creatinine, blood urea nitrogen, creatinine clearance, UA excretion, UA clearance, and plasma levels of aspirin.

RESULTS

At the lowest dosage, aspirin caused a 15% decrease in the rate of UA excretion (P = 0.045 by t-test), which was associated with a slight but significant increase in serum levels of UA (P = 0.009). These effects on UA levels were gradually reduced with increasing dosages of aspirin (multivariate analysis of variance with repeated measures showed no statistically significant difference in the rate of UA excretion between weeks 1-3 and week 0 [baseline], but the difference in serum UA levels for the same comparison was statistically significant [P = 0.038]). Generally, creatinine and UA clearance rates paralleled each other during aspirin treatment. However, 1 week after aspirin was discontinued, creatinine clearance remained decreased while UA clearance returned to baseline. Plasma aspirin concentrations were low and variable. However, patients with above-median aspirin levels had significantly greater changes in serum creatinine levels, urinary UA excretion rates, and UA clearance rates following the first week of aspirin treatment. Hypoalbuminemia and concomitant treatment with diuretics enhanced the effects of aspirin on renal function and UA retention.

CONCLUSION

Mini-dose aspirin, even at a dosage of 75 mg/day, caused significant changes in renal function and UA handling within 1 week in a group of elderly inpatients, mainly in those with preexisting hypoalbuminemia. Given the widespread (and often unmonitored) use of mini-dose aspirin, especially among the elderly, these findings call for clinician alertness as well as for further studies to clarify the mechanisms underlying these phenomena.

Aspirin absorption rates and platelet inhibition times with 325-mg buffered aspirin tablets (chewed or swallowed intact) and with buffered aspirin solution

Large clinical trials such as the second International Study of Infarct Survival routinely gave patients with myocardial infarction a chewed aspirin, yet there are no data to show whether chewing of aspirin is better, or worse, than swallowing a whole tablet. We performed a randomized, placebo-controlled study to determine whether chewing aspirin or administering it in solution accelerates its absorption and antiplatelet activity. On separate days, 12 fasting volunteers ingested 325 mg of buffered aspirin, either by chewing a tablet for 30 seconds before swallowing it with 4 ounces of water, swallowing a whole tablet with 4 ounces of water, or drinking 4 ounces of Alka Seltzer. Frequent blood samples were obtained for serum aspirin, salicylate, and thromboxane B2 (TxB2) concentrations. With all formulations of aspirin, serum TxB2 decreased 50% when the plasma aspirin concentration reached approximately 1,000 ng/ml. A 50% and 90% decrease in serum TxB2 occurred more quickly after chewing a tablet than after a tablet was swallowed whole. For example, the t 50% for serum TxB2 inhibition was 5.0 +/- 0.6 minutes with the chewed tablet versus 12.0 +/- 2.3 minutes when the tablet was swallowed (p = 0.01). A 50% decrease in serum TxB2 occurred 7.6 +/- 1.2 minutes after Alka Seltzer solution (p = 0.04 vs chewing a tablet; p = 0.13 vs swallowing a whole tablet). Chewing an aspirin tablet is the most effective way of accelerating absorption of aspirin into the blood and shortening the time required for an antiplatelet effect.

[Therapy of acute coronary syndrome. Aspirin, heparin, low-molecular-weight heparin, hirudin and GP-IIb/IIIa blockers]

Plaque rupture with consecutive formation of an intraluminal, platelet-rich thrombus is the central mechanism leading to critical reduction of coronary perfusion in the acute coronary syndrome. Current therapeutic strategies aim at the inhibition of activation of platelets and the coagulation cascade and the suppression of platelet aggregation and fibrin formation. The use of acetylsalicylic acid (ASA) is well established in the therapy of the acute coronary syndrome and its efficacy is documented in several large clinical studies. The results of a respective metaanalysis by the Antiplatelet Trialists' Collaboration are shown in Table 1. Further risk reduction has been achieved with the additional application of heparin during the early phase of treatment. Table 2 shows the results of the Montreal Heart Study of combined vs single drug treatment, and Figure 1 a metaanalysis by Oler et al. of combination therapy with heparin plus ASA compared to monotherapy with ASA. In the past, hirudin and analogues were not superior to heparin as adjunctive treatments to lysis in acute myocardial infarction, but bleeding complications were more frequent. In contrast, in the recently published OASIS-2 study, outcome in patients with unstable angina pectoris was significantly better with hirudin than with heparin. Several large studies have demonstrated at least equivalent efficacy of LMWHs compared to standard heparin. For the early phase of the acute coronary syndrome, the FRIC and ESSENCE studies have even demonstrated improved clinical outcome without increase in bleeding complications. However, in TIMI 11 and FRAXIS, long-term application of LMWH resulted in more bleeding complications and, in FRAXIS, in a trend to a worse clinical outcome. The use of GP-IIb/IIIa blockers, especially the chimeric antibody fragment abciximab, is well established in interventional cardiology. Figure 2 shows the mechanism of action of the GP-IIb/IIIa blockers on platelet aggregation. In addition, their use in conjunction with ASA and heparin in the acute coronary syndrome led to further significant reduction of cardiovascular events in several studies. For example, the reduction of events by abciximab in the CAPTURE-study is delineated in Table 3. The results obtained with several of the new competitive GP-IIb/IIIa receptor antagonists are shown in Table 4.

Pharmacokinetics and pharmacodynamics of sibrafiban, an orally administered IIb/IIIa antagonist, in patients with acute coronary syndrome

Sibrafiban is a double prodrug that is converted to the inactive single prodrug and to the active IIb/IIIa antagonist following oral administration. Pharmacokinetics (PK) and pharmacodynamics (PD) of oral sibrafiban and its metabolites were evaluated in patients postacute coronary syndrome receiving once- or twice-daily sibrafiban for up to 28 days at several dose levels. Mean peak concentrations of sibrafiban were < 5 ng/mL. Peak single prodrug concentrations occurred 1.7 +/- 1.0 (mean +/- SD) hours after sibrafiban dosing. Total apparent plasma clearance of the single prodrug was 40 +/- 15 L/h, and the elimination half-life was 2.3 +/- 0.8 hours. Mean values of the steady-state pharmacokinetics for total concentrations of the active drug over all doses were: time to peak plasma concentration, 5.0 +/- 1.7 hours; apparent clearance, 13.9 +/- 3.9 L/h; and half-life, 11.0 +/- 2.8 hours. Once-daily dosing resulted in high peak-trough excursions in active drug concentrations: trough concentrations were 21% +/- 6% of peak. Twice-daily dosing resulted in an AUC for the active drug on Day 28 that was 168% +/- 36% of that on Day 1, and steady-state trough concentrations were 54% +/- 10% of peak with sustained inhibition of platelet aggregation. Dose-adjusted steady-state active drug concentrations increased with increasing age and with decreasing renal function and body weight.

Impaired antiplatelet effects of aspirin associated with hypoxia and ATP release from erythrocytes. Studies in a system with flowing human blood

BACKGROUND

We have explored how hypoxic conditions may affect the antiplatelet effects of aspirin.

MATERIALS AND METHODS

For this purpose, a perfusion system containing a damaged vessel segment was modified in order to induce hypoxia (low Po2) in flowing blood. Blood samples were incubated with 50 mumol L-1 aspirin and divided into two aliquots, one being perfused under standard conditions (normoxic) and the other under hypoxic conditions. The interaction of platelets with the subendothelium was morphometrically evaluated.

RESULTS

In studies with untreated blood under normoxic conditions, platelet interaction with the subendothelium was 0.3 +/- 0.1% of contact, 5.3 +/- 1.6% of adhesion, 24.3 +/- 3.3% of thrombus and 29.9 +/- 2.7% of total covered surface. Aspirin-treated blood perfused under normoxic conditions showed a marked decrease in thrombus with a concomitant increase in both platelet adhesion and covered surface percentages. However, when aspirin-treated blood was perfused under hypoxic conditions, platelet interaction was not significantly different from that observed in untreated blood. Hypoxia induced a 10-fold increase in ATP release from erythrocytes in the perfusates. If apyrase was added to the perfusates, ATP release was prevented and aspirin effects were evident again.

CONCLUSION

Our results suggest that, under hypoxic conditions, the presence of aspirin would not help to inhibit further platelet activation.

Systemic biosynthesis of prostacyclin by cyclooxygenase (COX)-2: the human pharmacology of a selective inhibitor of COX-2

Prostaglandins (PG) are synthesized by two isoforms of the enzyme PG G/H synthase [cyclooxygenase (COX)]. To examine selectivity of tolerated doses of an inhibitor of the inducible COX-2 in humans, we examined the effects of celecoxib on indices of COX-1-dependent platelet thromboxane (Tx) A2 and on systemic biosynthesis of prostacyclin in vivo. Volunteers received doses of 100, 400, or 800 mg of celecoxib or 800 mg of a nonselective inhibitor, ibuprofen. Ibuprofen, but not celecoxib, significantly inhibited TxA2-dependent aggregation, induced ex vivo by arachidonic acid (83 +/- 11% vs. 11. 9 +/- 2.2%; P < 0.005) and by collagen. Neither agent altered aggregation induced by thromboxane mimetic, U46619. Ibuprofen reduced serum TxB2 (-95 +/- 2% vs. -6.9 +/- 4.2%; P < 0.001) and urinary excretion of the major Tx metabolite, 11-dehydro TxB2 (-70 +/- 9.9% vs. -20.3 +/- 5.3%; P < 0.05) when compared with placebo. Despite a failure to suppress TxA2-dependant platelet aggregation, celecoxib had a modest but significant inhibitory effect on serum TxB2 4 hr after dosing. By contrast, both ibuprofen and celecoxib suppressed a biochemical index of COX-2 activity (endotoxin induced PGE2 in whole blood ex vivo) to a comparable degree (-93.3 +/- 2% vs. -83 +/- 6.1%). There was no significant difference between the doses of celecoxib on COX-2 inhibition. Celecoxib and ibuprofen suppressed urinary excretion of the prostacyclin metabolite 2,3 dinor 6-keto PGF1alpha. These data suggest that (i) platelet COX-1-dependent aggregation is not inhibited by up to 800 mg of celecoxib; (ii) comparable COX-2 inhibition is attained by celecoxib (100-800 mg) and ibuprofen (800 mg) after acute dosing; and (iii) COX-2 is a major source of systemic prostacyclin biosynthesis in healthy humans.

Antiplatelet therapy. Aspirin, ticlopidine/clopidogrel, and anti-integrin agents

Aspirin is the most widely employed antithrombotic agent in use today and has a proven role in the prevention and acute management of atherosclerosis-associated arterial thrombotic events. More recently developed antiplatelet agents have been found to have specific prophylactic roles associated with percutaneous coronary intervention and other clinical settings. This article outlines pharmacologic considerations and current clinical knowledge relevant to the use of aspirin, ticlopidine, clopidogrel, and the GPIIbIIIa antagonists in the management of thrombotic disorders.

Focused antithrombotic therapy: novel anti-platelet salicylates with reduced ulcerogenic potential and higher first-pass detoxification than aspirin in rats

The use of aspirin as an anti-platelet drug is limited by its propensity to induce gastric injury and by its adverse effect on vascular prostacyclin formation. Two phenolic non-steroidal anti-inflammatory drugs (salicylic acid and diflunisal) were modified by esterification with a series of O-acyl moieties. The short-term ulcerogenic in vitro and in vivo anti-platelet properties, pharmacodynamic profiles, and extent of hepatic extraction of these phenolic esters were compared with aspirin (acetylsalicylic acid). The more lipophilic esters (longer carbon chain length in O-acyl group) show significantly less gastrotoxicity in stressed rats than does aspirin after a single oral dose. The in vitro and in vivo anti-platelet studies show that these phenolic esters inhibited (1) arachidonate-triggered human platelet aggregation and (2) thrombin-stimulated rat serum thromboxane A2 production by platelets in the clotting process almost as effectively as aspirin. The hepatic extractions of these O-acyl derivatives are significantly higher than those of aspirin. The pharmacodynamic studies show that these O-acyl derivatives of salicylic acid and diflunisal probably bind to, or combine with, the same site on the platelet cyclooxygenase as aspirin. Replacing the O-acetyl group with longer chain O-acyl moiety in this series of phenolic esters markedly reduced the potential of these agents to induce short-term gastric injury but did not lessen their activity as inhibitors of platelet aggregation. These non-acetyl salicylates may therefore represent a novel class of anti-platelet drugs with less ulcerogenic potential.

Pharmacodynamic aspects of sustained release preparations

The sustained release (SR) mode of drug administration has certain features that have an important impact on the magnitude of the pharmacologic response: (a) it minimizes fluctuation in blood drug concentrations (i.e. between peak and trough). However, due to the pronounced non-linear relationship between drug concentration and pharmacologic effect (i.e. pharmacodynamics) the impact of this property differs considerably as a function of the shape of the pharmacodynamic profile and the position of the specific range of concentrations on the curve of this profile; (b) it produces a slow input rate which tends to minimize the body's counteraction to the drug's intervening effect on regulated physiological processes; and (c) it provides a continuous mode of drug administration. This important pharmacodynamic characteristic may produce, in certain cases, an opposite clinical effect than that attained by an intermittent (pulsatile) mode of administration of the same drug. For many drugs with non-concentration-dependent pharmacodynamics, the exposure time, rather than the AUC, is the relevant parameter and it can therefore be optimized by SR preparations. The slow input function may minimize hysteresis in cases where the site of action is not in a rapid equilibrium with the blood circulation. The pharmacodynamics of the desired effect(s) and/or adverse effect(s) may also be influenced by the site of administration, especially in cases where the drug is delivered directly to its site of action. These factors demonstrate the important influence of the mode of administration on the pharmacological and clinical outcomes. In addition, they highlight the need to include these pharmacodynamic considerations in all stages from drug development to the optimization of their clinical use.

The effect of aspirin on thrombin stimulated platelet adhesion receptor expression and the role of neutrophils

AIMS

Aspirin has proven clinical efficacy in limiting the thrombotic complications of atherosclerotic vascular disease but its mechanism of action remains unclear. Recent evidence suggests the anti-platelet action of aspirin may be partly mediated by neutrophil derived nitric oxide (NO). The aim of the study was to determine the effects of aspirin on thrombin-induced platelet expression of the alpha-granule membrane protein, P-selectin, and the platelet surface glycoprotein required for aggregation, GPIIb-IIIa, and to assess whether this was enhanced by the presence of neutrophils.

METHODS

Platelet P-selectin and GPIIb-IIIa receptor expression were assessed by flow cytometric analysis of washed platelets stimulated with thrombin (0.025 iu ml(-1), sub aggregatory concentration) alone or after pre-incubation with aspirin (0.05, 0.1, 0.5, 1.0 mg m1(-1) either in the presence or absence of neutrophils (100 platelets per neutrophil). NO release was determined by assay of nitrite in the supernatants from parallel samples.

RESULTS

In preliminary aggregation studies, aspirin at all concentrations inhibited arachidonic acid but not thrombin-induced platelet aggregation. Similarly, aspirin at all concentrations failed to inhibit thrombin-induced platelet P-selectin or GPIIb-IIIa expression and this was not influenced by the presence of neutrophils. A reduction in P-selectin and GPIIb-IIIa receptor density on non-activated platelets co-incubated with unstimulated neutrophils was associated with NO release from neutrophils, but this was not enhanced by the addition of aspirin.

CONCLUSIONS

These results confirm that thrombin-induced platelet alpha-granule release, with consequent P-selectin expression, and platelet GPIIb-IIIa expression, are not affected by aspirin inhibition of cyclo-oxygenase and suggest that the anti-thrombotic efficacy of aspirin in vivo may partly depend on other mechanisms. This study did not demonstrate an effect of neutrophils or neutrophil derived NO on aspirin inhibition of platelet adhesion receptor expression.

Hepatic structure-pharmacokinetic relationships: the hepatic disposition and metabolite kinetics of a homologous series of O-acyl derivatives of salicylic acid

1. The hepatic disposition and metabolite kinetics of a homologous series of O-acyl (acetyl, propionyl, butanoyl, pentanoyl, hexanoyl and octanoyl) esters of salicylic acid (C2SA, C3SA, C4SA, C5SA, C6SA and C8SA, respectively) was determined using a single-pass, in-situ rat liver preparation. 2. The hepatic venous outflow profiles for the parent esters and the generated metabolite, salicylic acid (SA) were analysed by HPLC. Non-parametric moments analysis was used to determine the area under the curve (AUC'), mean transit time (MTT) and normalized variance (CV2) for the parent esters and generated SA. 3. Pregenerated SA ([14C]-salicylic acid) was injected into each liver with the parent ester to determine its distribution characteristics. 4. The overall recovery of ester plus metabolite was 89% of the ester dose injected and independent of the ester carbon number, suggesting that ester extraction was due to hepatic metabolism to salicylic acid. 5. The metabolite AUC' value increased directly with the lipophilicity of the parent ester (from 0.12 for C2SA to 0.95 for C8SA). By contrast, the parent AUC' decreased with the lipophilicity (from 0.85 for C2SA to zero for C8SA). The metabolite MTT value also showed a trend to increase with the lipophilicity of the parent ester (from 15.72 s for C3SA to 61.97 s for C8SA). However, the parent MTT value shows no significant change across the series. 6. The two-compartment dispersion model was used to derive the kinetic parameters for parent ester, pregenerated SA and generated SA. Consequently, these parameters were used to estimate the values of AUC', MTT and CV2 for the parent ester and metabolite. The moments values obtained using the two-compartment dispersion model show similar trends to the corresponding moments values obtained from the outflow profiles using a non-parametric approach. 7. The more lipophilic aspirin analogues are more confined to the portal circulation after oral administration than aspirin due to their more extensive hepatic elimination avoiding systemic prostacyclin inhibition. Given that aspirin's selectivity as an anti-thrombotic agent has been postulated to be due to selective anti-platelet effects in the portal circulation, the more lipophilic and highly extracted analogues are potentially more selective anti-thrombotic agents than aspirin.

Hepatic disposition and metabolite kinetics of a homologous series of diflunisal esters

The hepatic disposition and metabolite kinetics of a homologous series of diflunisal O-acyl esters (acetyl, butanoyl, pentanoyl, and hexanoyl) were determined using a single-pass perfused in situ rat liver preparation. The experiments were conducted using 2% BSA Krebs-Henseleit buffer (pH 7.4), and perfusions were performed at 30 mL/min in each liver. O-Acyl esters of diflunisal and pregenerated diflunisal were injected separately into the portal vein. The venous outflow samples containing the esters and metabolite diflunisal were analyzed by high performance liquid chromatography (HPLC). The normalized outflow concentration-time profiles for each parent ester and the formed metabolite, diflunisal, were analyzed using statistical moments analysis and the two-compartment dispersion model. Data (presented as mean +/- standard error for triplicate experiments) was compared using ANOVA repeated measures, significance level P < 0.05. The hepatic availability (AUC'), the fraction of the injected dose recovered in the outflowing perfusate, for O-acetyldiflunisal (C2D = 0.21 +/- 0.03) was significantly lower than the other esters (0.34-0.38). However, RN/fu, the removal efficiency number RN divided by the unbound fraction in perfusate fu, which represents the removal efficiency of unbound ester by the liver, was significantly higher for the most lipophilic ester (O-hexanoyldiflunisal, C6D = 16.50 +/- 0.22) compared to the other members of the series (9.57 to 11.17). The most lipophilic ester, C6D, had the largest permeability surface area (PS) product (94.52 +/- 38.20 mL min-1 g-1 liver) and tissue distribution value VT (35. 62 +/- 11.33 mL g-1 liver) in this series. The MTT of these O-acyl esters of diflunisal were not significantly different from one another. However, the metabolite diflunisal MTTs tended to increase with the increase in the parent ester lipophilicity (11.41 +/- 2.19 s for C2D to 38.63 +/- 9.81 s for C6D). The two-compartment dispersion model equations adequately described the outflow profiles for the parent esters and the metabolite diflunisal formed from the O-acyl esters of diflunisal in the liver.

Antiplatelet therapy in atherosclerotic cardiovascular disease

Arterial thrombosis frequently leads to death or disability from stroke, peripheral arterial disease, or myocardial infarction (MI). Treating the underlying causes of these diseases is the key to producing significant reduction in morbidity, mortality, and health care costs. Prevention of arterial thrombosis is the primary indication for antiplatelet therapy, and intense research has been conducted in the past decade to develop novel antiplatelet agents with favorable safety profiles. The results of the Antiplatelet Trialists' Collaboration, which definitively established the rationale for antiplatelet agents in the prevention of death, MI, and stroke, were an important stimulus for this research. This large meta-analysis combined data from 145 randomized trials and showed that antiplatelet therapy (most commonly aspirin, 75 to 325 mg/d) reduced the risk of vascular events, including nonfatal MI, nonfatal stroke, and vascular death, by 25% in patients at high risk for occlusive vascular disease. The limitations and adverse effects associated with traditional antiplatelet agents such as aspirin have prompted the search for newer antiplatelet agents. Clinical trials such as the Clopidogrel versus Aspirin in Patients at Risk of Ischemic Events (CAPRIE) study, which was the first study to evaluate aspirin and clopidogrel in patients with cerebrovascular, cardiac, and peripheral arterial disease, have established the importance of newer antiplatelet effects in the management of patients with diseases associated with atherosclerosis. The pathophysiology of atherosclerosis, the mechanisms of action of antiplatelet agents, and the results of these and other clinical trials that document the value of antiplatelet agents in atherosclerosis are reviewed in this paper.

Thromboembolic complications several days after a single-dose administration of aspirin

The antithrombotic properties of acetyl salicylic acid (ASA) used at current doses are largely demonstrated. However, our previous study showed unexpected thrombotic potencies associated with the use of this drug. In this study we investigate the effect of aspirin on an experimental thrombosis induced by laser beams, according to its in vivo plasma concentration. Experiments were done on nine groups of seven Wistar male rats. The groups are defined by the delay between aspirin administration time and the laser-induced thrombosis time. Results from this study showed an enhancement of thromboembolic complications when thrombosis was induced 8 or 10 days after aspirin administration; the number of emboli and the duration of embolization are increased, compared to the control group. The prothrombotic properties of ASA demonstrated in this study, might limit its therapeutic benefit and might explain thromboembolic complications observed in some ASA-treated patients. These results also suggest a biological monitoring several days after aspirin administration to patients.

Inhibition of ultraviolet B-induced activator protein-1 (AP-1) activity by aspirin in AP-1-luciferase transgenic mice

Aspirin is under consideration as a promising chemopreventative agent for human cancers. To study the usefulness of aspirin as a chemopreventative agent for UV-induced human skin cancer, we investigated the effect of aspirin on UVB-induced activator protein-1 (AP-1) activity. In the JB6 cell culture system, aspirin or sodium salicylate (SA) inhibited UVB-induced AP-1 activity in a dose-dependent manner; this inhibitory effect occurred only in cells pretreated with aspirin or SA before UVB irradiation but not cells treated with aspirin or SA after UVB irradiation. Furthermore, these inhibitory effects on UVB-induced AP-1 activity appeared to be mediated through blocking of activation of MAP kinase family members, including extracellular signal-regulated protein kinases, c-Jun N-terminal kinases, and p38. It was not due to absorption of UVB light by aspirin. In the skin of AP-1-luciferase transgenic mice, UVB irradiation induced a rapid increase in AP-1 activity, which reached the peak at 48 h post-UVB irradiation. The topical pretreatment of mouse skin with aspirin markedly blocked the UVB-induced AP-1 transactivation in vivo. These data provide the first evidence that aspirin and SA are inhibitors of UV-induced signal transduction and thus could be used as a chemopreventative agent for skin cancer.

Platelet activation and inhibition in unstable coronary syndromes

Platelet activation occurs episodically in unstable angina, as reflected by enhanced thromboxane metabolite excretion, and most episodes can be suppressed by low-dose aspirin. Biochemical evidence of platelet activation and electrocardiographic evidence of myocardial ischemia are often temporally dissociated, thus suggesting the likely involvement of different triggers. Aspirin is effective in reducing the short-term and long-term risks of myocardial infarction and death by 40-60%, in a dose-independent fashion consistent with the saturability of platelet cyclo-oxygenase inhibition at low doses. Suppression of platelet thromboxane synthesis by aspirin and the blockade of platelet adenosine diphosphate receptors by ticlopidine or clopidogrel appear to have a similar impact on limiting the risk of a thrombotic outcome of plaque fissuring, thereby suggesting combined strategies for future studies.

Percutaneous absorption of salicylic acid after repeated (14-day) in vivo administration to normal, acnegenic or aged human skin

The objective of the present work was to determine the relative bioavailability of salicylic acid (SA) after repeated (14-day) topical application to subjects who presented normal, acnegenic, or photodamaged facial skin. To emulate exposure characteristics likely to be encountered by subjects in these two subpopulations, individuals presenting facial acne were treated with 2% SA in a hydroalcoholic vehicle, and volunteers with aged or photodamaged skin received a comparable topical dose of SA in a cream (moisturizer-like) vehicle. Plasma concentration-time profiles and cumulative urinary excretion of SA were measured after the last dose in subjects who had received 15 consecutive daily topical applications of 27 mg of SA or oral doses of 81 mg of acetylsalicylic acid (ASA). The rate and extent of percutaneous absorption of SA were not affected by facial skin condition. Faster rates of absorption (Cmax) were obtained with a hydroalcoholic compared with a cream vehicle. Systemic SA exposures were at least five-fold higher with oral ASA than topical SA. Based on systemic salicylate concentrations resulting from ingestion of 81 mg of ASA, these results support that patients without gross skin disorders are at minimal risk of adverse systemic effects from routine use of topical products containing 2% SA.

Effect of aspirin dosage and enteric coating on platelet reactivity

Although aspirin is effective in the prevention and treatment of cardiovascular diseases, the optimal dose remains uncertain. The purpose of this study was to compare the platelet inhibitory and prostacyclin-sparing effects of 2 doses (81 and 325 mg) and forms (enteric-coated and regular) of aspirin. Since platelet reactivity has been reported to increase after strenuous exercise, a known trigger of myocardial infarction, subjects were studied following maximal treadmill exercise as well as at rest. Forty male healthy subjects were evaluated using a randomized, double-blind, parallel study design. Blood samples were obtained before and after maximal treadmill exercise at baseline and after 7 days on aspirin therapy. Both enteric and regular aspirin in 81- and 325-mg dosages markedly inhibited adenosine diphosphate and epinephrine-induced aggregation at rest and after exercise. Aspirin also inhibited the platelet response to collagen as assessed by a longer lag time to aggregation. The prolongation of lag time was greater for 325 mg than for 81 mg (100 +/- 7 vs 91 +/- 7; p = 0.04, after exercise). There were no significant dose-related differences in plasma 6-keto-prostaglandin F1alpha level; however, enteric-coated aspirin inhibited the exercise-induced increase in 6-keto-prostaglandin F1alpha to a lesser extent than regular aspirin. Although both doses (81 and 325 mg) and types (regular and enteric-coated) of aspirin inhibited adenosine diphosphate and epinephrine-induced aggregation equally, the 325-mg dose inhibited collagen-induced aggregation to a greater extent than 81 mg. The greater platelet inhibition observed with 325 mg may be clinically relevant in acute coronary syndromes characterized by plaque rupture with extensive collagen exposure and platelet activation.

Aspirin inhibits expression of the interleukin-1beta-inducible group II phospholipase A2

Nonsteroidal anti-inflammatory drugs (NSAIDs) clearly inhibit the synthesis and release of prostaglandins. However, these actions are not sufficient to explain all the anti-inflammatory effects of these drugs. Recently, it has been shown that aspirin and sodium salicylate inhibit the activation of the transcription factor NF-kappaB. Group II phospholipase A2 (sPLA2) is expressed in rat glomerular mesangial cells upon exposure to the inflammatory cytokine interleukin-1beta (IL-1beta) and this induction is attenuated by the NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC). We now report that aspirin inhibits the IL-1beta-induced sPLA2 activity in rat mesangial cells in a dose-dependent manner. The IC50 value of aspirin for sPLA2 inhibition was 6.5 mM. This decrease in sPLA2 activity was not due to direct inhibition of enzymatic activity but rather to the fact that aspirin inhibits the expression of IL-1beta-induced sPLA2 protein and mRNA. Furthermore, by electrophoretic mobility shift analysis we demonstrate reduced DNA binding of the nuclear factor kappaB, an essential component of the IL-1beta-dependent upregulation of sPLA2 gene transcription, after treatment of the cells with aspirin. The study described in this report indicates that the inhibition of sPLA2 expression as induced by pro-inflammatory cytokines potentially represents an additional mechanism of action for aspirin.