Salicylic acid inhibition of the irreversible effect of acetylsalicyclic aicd on prostaglandin synthetase may be due to competition for the enzyme cationic binding site

Bioassay-guided detection, identification and assessment of antibacterial and anti-inflammatory compounds from olive tree flower extracts by high-performance thin-layer chromatography linked to spectroscopy

Olive trees are one of the most widely cultivated fruit trees in the world. The chemical compositions and biological activities of olive tree fruit and leaves have been extensively researched for their nutritional and health-promoting properties. In contrast, limited data have been reported on olive flowers. The present study aimed to analyse bioactive compounds in olive flower extracts and the effect of fermentation-assisted extraction on phenolic content and antioxidant activity. High-performance thin-layer chromatography (HPTLC) hyphenated with the bioassay-guided detection and spectroscopic identification of bioactive compounds was used for the analysis. Enzymatic and bacterial in situ bioassays were used to detect COX-1 enzyme inhibition and antibacterial activity. Multiple zones of antibacterial activity and one zone of COX-1 inhibition were detected in both, non-fermented and fermented, extracts. A newly developed HPTLC-based experimental protocol was used to measure the high-maximal inhibitory concentrations (IC50) for the assessment of the relative potency of the extracts in inhibiting COX-1 enzyme and antibacterial activity. Strong antibacterial activities detected in zones 4 and 7 were significantly higher in comparison to ampicillin, as confirmed by low IC50 values (IC50 = 57-58 µg in zone 4 and IC50 = 157-167 µg in zone 7) compared to the ampicillin IC50 value (IC50 = 495 µg). The COX-1 inhibition by the extract (IC50 = 76-98 µg) was also strong compared to that of salicylic acid (IC50 = 557 µg). By comparing the locations of the bands to coeluted standards, compounds from detected bioactive bands were tentatively identified. The eluates from bioactive HPTLC zones were further analysed by FTIR NMR, and LC-MS spectroscopy. Multiple zones of antibacterial activity were associated with the presence of triterpenoid acids, while COX-1 inhibition was related to the presence of long-chain fatty acids.

Antioxidant effect of acetylsalicylic and salicylic acid in rat brain slices subjected to hypoxia

Acetylsalicylic acid (ASA) reduces the incidence of ischemic stroke mainly through its antithrombotic action; however, it also has a direct neuroprotective effect. The present study was designed to evaluate the effect of ASA on oxidative stress and the activity of nitric oxide synthase (NOS) in an in vitro model of hypoxia in rat brain slices. Rat brain slices were perfused with nitrogen (hypoxia) for a maximum of 120 min, after which we measured lipid peroxidation, glutathione levels, glutathione-related enzyme activities, and constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) activities. In brain tissue subjected to hypoxia, ASA reduced oxidative stress and iNOS activity (all increased by hypoxia), but only when used at higher concentrations. The effects of salicylic acid (SA) were similar but more intense than were those of ASA. After oral administration, the effect of SA was much greater than that of ASA, and the decrease in cell death with SA was seen much more clearly. In view of the greater effect of SA compared to ASA on changes in oxidative stress parameters in a model of hypoxia, and higher brain concentrations of SA when it is administered alone than when ASA is given (undetectable levels), we conclude that SA plays an important role in the cytoprotective effect in brain tissue after ASA administration.

Prostaglandins, their inhibitors and cancer

Prostaglandins (PGs) and their analogs endoperoxides are a large series of compounds which mainly enhanced cancer development and progression, acting as cocarcinogens or tumor promoters, and having profound effects on carcinogenesis. Although PGs are ubiquitous tissue hormones exerting pleiotropic effects on cancer cells, their mechanism(s) of action at molecular and cellular levels are not yet elucidated. Autoradiographic, ultrastructural, antigenic, and cell surface studies revealed that PGs act namely by their specific receptors and by interfering with DNA, RNA and protein synthesis, cell membranes and cell communications. PGs also play a role in tumor immunology and transplantation, acting as immunomodulators. Prostaglandins exert their effects by autocrine and paracrine mechanisms similar to hormone-like substances, and hypophysectomy reduces some of their tumor-promoting effects. PGs may act synergistically with hormones, growth factors (GFs), and vitamins. Several drugs called PG-synthesis inhibitors or PG-antagonists are found to markedly inhibit the cyclooxygenase activity. Most of these PG-inhibitors (aspirin, ibuprofen, indomethacin, piroxicam, sulindac) or commonly called NSAIDs (nonsteroidal antiinflammatory drugs) also significantly inhibit cancer development and cancer progression, and are recently used in epidemiological studies for cancer prevention and treatment. Developing more active and less toxic NSAIDs, which can also more selectively inhibit PG synthesis, is a promising field in prostaglandin research.

Effects and interaction studies of triflusal and other salicylic derivatives on cyclooxygenase in rats

Triflusal (TR) is a new salicylic acid derivative used clinically as an antiplatelet drug. Both aspirin (ASA) and TR inhibit platelet cyclooxygenase but the effects of these drugs are different. TR (0.5-2 mM) strongly inhibited platelet aggregation and malondialdehyde formation induced by arachidonic acid. The IC50 was 0.8 mM for TR and less than 0.1 mM for ASA. Deacetylated compounds, salicylic acid (SA) and HTB (the main metabolite of TR) were apparently competitive and reversible inhibitors of cyclooxygenase and HTB was 15 times more potent than SA. They did, however, partially prevent the inhibitory effects of ASA and TR in vitro. A similar effect was observed ex vivo in rats treated with HTB (100 mg/k i.p.) before TR or ASA (20 and 5 mg/kg i.v., respectively). Moreover, TR at 10 and 20 mg/kg i.v., inhibited thromboxane production by more than 50% while its effect on vascular cyclooxygenase was negligible. These findings indicated that TR is a weaker inhibitor of cyclooxygenase than ASA, and that HTB interferes with the effect of TR and ASA, despite the fact that HTB is a more potent reversible inhibitor than SA with probably a higher affinity for this enzyme.

Salicylate measurement: clinical usefulness and methodology

The salicylates are the most commonly used analgesic, antipyretic, and anti-inflammatory drugs. They are available in hundreds of preparations, many of which are over-the-counter medications. The easy access to large quantities of the drug and the widespread perception that the drug is harmless have contributed to salicylate intoxication becoming a serious and common problem, particularly among the pediatric and geriatric populations. Salicylate is still the major drug for the treatment of rheumatic diseases. The use of salicylate in high doses for the management of these patients requires close monitoring of serum salicylate levels because of the large interindividual variation in dose-serum level relationships and the narrowness of the therapeutic range. Thus, both for the management of patients intoxicated with salicylate and patients who are on high-dose salicylate therapy, the measurement of serum salicylate levels is an important clinical laboratory service. Recent research on the inhibitory effect of aspirin on platelet aggregation has led to the prophylactic use of aspirin in low doses as an antithrombotic drug. This new therapeutic use of aspirin can be aided by monitoring low serum levels of salicylate and perhaps aspirin itself. This article reviews the current state of the knowledge of the pharmacokinetics and clinical toxicology of salicylate, the clinical usefulness of salicylate measurement by the clinical laboratory, and recent development in the analytical technology for salicylate analysis.

Pharmacology of platelet inhibition in humans: implications of the salicylate-aspirin interaction

The current dispute over the effects of "low" vs "high" doses of aspirin should take into consideration the pharmacokinetics of this drug. In fact, different pharmaceutical formulations of aspirin may deliver little or no aspirin to the systemic blood. This was the case, for instance, in healthy volunteers taking 320 mg of compressed aspirin or 800 mg of enteric-coated aspirin. In all instances thromboxane B2 generation in serum was fully inhibited. Platelet cyclooxygenase might therefore be effectively acetylated by exposure to aspirin in the portal circulation, whereas vascular cyclooxygenase could be spared. Thus aspirin formulations ensuring complete first-pass deacetylation should be sought rather than "low" or "high" doses of unspecified aspirin formulations. Regardless of the type and dose of aspirin administered, salicylate is formed and accumulates in the circulation. It may antagonize the effects of aspirin on cyclooxygenase, at least in acute conditions. As an example, after administration of 1 g of salicylate to healthy volunteers, when plasma levels of the drug were about 75 micrograms/ml, the effect of 40 mg iv aspirin (given 40 min later) on platelet cyclooxygenase and aggregation was significantly diminished. In contrast, in patients undergoing saphenectomy, the same dose of salicylate (1 g) gave plasma drug levels of about 25 micrograms/ml; salicylate was unable to prevent the inhibitory effect on platelets of 40 mg iv aspirin (given 1 hr later) but did act on vascular prostacyclin. Thus the combination of salicylate with aspirin at an appropriate dose and blood level ratio may result in almost complete dissociation of the drug's effect on platelets and vessels in man.(ABSTRACT TRUNCATED AT 250 WORDS)

Preparation and analysis of deuterium-labeled aspirin: application to pharmacokinetic studies

Inhibition of endogenous prostacyclin and thromboxane biosynthesis by aspirin is critically dose-dependent in humans. Gastrointestinal and hepatic hydrolysis may limit systemic availability of aspirin, especially in low doses, perhaps contributing to the biochemical selectivity of aspirin. Existing analytical methods do not permit determination of systemic bioavailability when low (less than 100 mg) doses of aspirin are administered. Deuterium-labeled aspirin (2-acetoxy[3,4,5,6-2H4]benzoic acid) was synthesized from salicylic acid by catalytic exchange and subsequent acetylation. Analysis of the compounds as benzyl esters by GC-MS followed extractive alkylation from plasma. Heptadeuterated compounds were used as internal standards. Simultaneous administration of tetradeuterated aspirin intravenously with native aspirin orally to anesthetized dogs permitted kinetic studies of both aspirin and salicylic acid. The sensitivity of the method is superior to published methods using HPLC and, thus, more applicable to studies of low dose aspirin. Pulse administration of stable isotope-labeled aspirin permits detailed and repeated studies of dose-related aspirin pharmacokinetics in humans.

Influence of intravenous acetylsalicylic acid and sodium salicylate on human renal function and lithium clearance

The influence of intravenous acetylsalicylic acid (ASA; D,L-lysine-mono-acetylsalicylate), equimolar doses of sodium salicylate (SA) and placebo (P) on renal function has been studied in 6 healthy female volunteers, in 150 mmol sodium balance, and in lithium (Li) steady state with a plasma Li between 0.6 and 0.8 mmol/l. Following a bolus injection of 0.5 g ASA, 0.444 g SA or P (50 ml saline) given over 10 min and a subsequent continuous infusion of 1.5 g ASA, 1.332 SA or P (150 ml saline) over 170 min, urine was collected for 3 h as well as 6 plasma samples at 30-min intervals. Plasma ASA levels were between 13.8 and 22.1 micrograms/ml and for SA they were 20.8 to 82.6 microgram/ml during ASA infusion, and between 22.5 and 108.9 microgram/ml for SA during SA infusion. Neither ASA nor SA caused a significant change in urine volume, in the renal clearances of Na, K, free water, osmolality, creatinine, inulin and p-aminohippurate (PAH) or in plasma Li level. Renal Li clearance was slightly reduced by SA, from 37.8 to 29.4 ml/min (p less than 0.05). Since renal prostaglandin (PG) synthesis (urinary PGE2 excretion) was 60.6% suppressed by ASA and was not affected by SA, the decrease in Li clearance cannot be related to inhibition of cyclooxygenase in the kidney.

Structure of the active site of prostaglandin synthase from studies of depsides: an alternate view

Evaluation of the structure of the lichen depside, 4-0-methylcryptochlorophaeic acid, the most potent inhibitor of prostaglandin synthesis known, and its potential interaction with heme supports a model of the active site of prostaglandin synthase initially suggested by studies of arachidonic acid-heme interaction.

Structural requirements for preventing the aspirin- and the arachidonate-induced inactivation of platelet cyclo-oxygenase: additional evidence for distinct enzymatic sites

2-Hydroxybenzoic acid (salicylic acid) prevents the inhibition by aspirin (ASA) of platelet aggregation and of the generation of thromboxane A2 from arachidonic acid (AA). We studied the ability of 2-hydroxybenzoic acid analogues to block ASA and to prevent the platelet desensitization due to a first exposure to AA. Inactivation was prevented when exposure to AA was done in the presence of reversible inhibitors of cyclo-oxygenase. Phenol, methyl salicylate and L8027 were thus strong inhibitors of AA-induced platelet activation and desensitization. The minimal structural requirement for inhibition of thromboxane A2 generation from AA was a phenol group as benzoic acid was fully inactive. 2-Hydroxybenzoic acid, and to some extent 2,6-dihydroxybenzoic acid were effective against ASA, the most active substances being methyl salicylate and L8027. The minimal structural requirement for blocking ASA was that 2-hydroxybenzoic acid, 2-methoxybenzoic acid should be devoid of activity, which highlights the fact that the hydroxyl group must be available. Our work favours the hypothesis that non-steroidal anti-inflammatory drugs react with two sites of cyclo-oxygenase, which were named the supplementary and the catalytic sites. The interaction of 2-hydroxybenzoic acid and of its analogues with the supplementary site is necessary but not sufficient for the efficacy of these compounds as cyclo-oxygenase inhibitors. The intensity of interaction with the supplementary site and the modifications of the catalytic site determine the potency of these compounds as cyclo-oxygenase inhibitors. For preventing ASA inactivation, an interaction with the supplementary sites is always necessary, but furthermore an appropriate group, preferentially in the position ortho to the hydroxyl, is needed.

Evidence that the peroxidase of the fatty acid cyclooxygenase acts via a Fenton type of reaction

Addition of ferrous sulfate to a solution containing peroxy-methyl arachidonate resulted in cleavage of the peroxy group on the methyl arachidonate as assessed by absorption at 232nm. The results suggest that ferrous iron can be involved in the reduction of fatty acid peroxides and supports the possibility that the peroxidase component of the fatty acid cyclooxygenase occurs via a Fenton type reaction.

Ibuprofen protects platelet cyclooxygenase from irreversible inhibition by aspirin

Previous investigations have shown that ibuprofen inhibits the second wave of platelet aggregation and blocks the conversion of 14C-arachidonic acid to thromboxane. However, the influence of the drug on platelet function and cyclooxygenase is transitory, lasting only 24 hours. The present study has taken advantage of the short-lived influence of ibuprofen to study its interaction with the long-term effects of aspirin. As expected, both aspirin and ibuprofen suppressed platelet cyclooxygenase activity and function, but addition of aspirin to ibuprofen-treated platelets did not increase the degree of inhibition in vitro. Platelet function and prostaglandin synthesis recovered completely 26 hours following ingestion of ibuprofen, but remained compromised 26 hours after taking aspirin. When 650 mg of aspirin was administered after ibuprofen, platelet function and cyclooxygenase activity recovered as completely at 26 hours as did platelets which had been exposed to ibuprofen alone. Thus, prior exposure to ibuprofen in vivo completely protected cyclooxygenase from the irreversible effects of aspirin. Our findings indicate that ibuprofen-like indomethacin and other nonsteroidal antiinflammatory drugs react with the heme group of cyclooxygenase to prevent arachidonic acid conversion. Since ibuprofen completely blocks the effects of aspirin in platelets in vitro and in vivo, aspirin's primary influence on inhibition of cyclooxygenase must also be through action on the heme portion of the enzyme, rather than acetylation of the protein.

Effect of acetaminophen and salicylate on aspirin-induced inhibition of human platelet cyclo-oxygenase

Recent studies have shown that salicylic acid, a metabolite of aspirin, effectively competes for the same site on the platelet cyclo-oxygenase enzyme. In the present investigation we have evaluated the effect of salicylate and acetaminophen on aspirin induced inhibition of cyclo-oxygenase and platelet function. Results of our studies show that both drugs at equimolar concentrations had no inhibitory effect on aspirin induced blockage of cyclo-oxygenase or platelet function. Even at higher concentrations acetaminophen failed to protect cyclo-oxygenase or prevent inhibition of platelet function by aspirin. Salicylate at concentrations above 5 mM effectively blocked the inhibition of cyclo-oxygenase activity and platelet aggregation in response to arachidonate.