Sodium salicylate interferes with the inhibitory effects of aspirin and indomethacin on human platelets

Inhibition of prostaglandin H2 synthases by salicylate is dependent on the oxidative state of the enzymes

At antipyretic and analgesic doses, salicylate has no antiplatelet or anti-inflammatory effects, unlike typical inhibitors of the prostaglandin H synthases (PGHSs). We demonstrated that salicylate inhibits PGHS-1 and -2 with a potency inversely related to ambient hydroperoxide concentrations. Salicylate inhibition of PGHS-1 was prevented by 12-hydroperoxyeicosatetraenoic acid (12-HPETE). Increasing the production of prostaglandin G2 (the peroxide product of PGHS-cyclooxygenase activity) by elevating the concentration of either enzyme or substrate reversed inhibition. Using analogs of benzoic acid differing only at the hydroxyl position, we revealed the importance of this moiety to salicylate's inhibitory mechanism. Unlike typical phenolic inhibitors, e.g., acetaminophen, salicylate was ineffective as a reducing cosubstrate for PGHS-peroxidase activity, implicating the cyclooxygenase site as its putative target. PGHS-cyclooxygenase activity depends upon the oxidation of an active site tyrosine by electron transfer to the oxidized ferriprotoporphyrin of the peroxidase. The PGHS-1 apoenzyme reconstituted with manganese protoporphyrin instead of iron protoporphyrin has very little peroxidase activity. 12-HPETE does not prevent the inhibition of Mn-PGHS-1 by salicylate, indicating that reversal of salicylate inhibition by hydroperoxides depends upon electron transfer between the cyclooxygenase and peroxidase active sites. These results are consistent with an inhibitory action of salicylate at the PGHS-cyclooxygenase site that is dependent on the PGHS-peroxidase activity.

Anti-inflammatory effects of aspirin and sodium salicylate

Aspirin (acetylsalicylic acid) is one of the most widely used drugs worldwide. It acetylates cyclooxygenases thereby irreversibly blocking the conversion of arachidonic acid to prostanoids. Biotransformation of aspirin yields salicylate, a compound that possesses similar anti-inflammatory potency as aspirin but lacks aspirin's inhibitory effect on the activity of isolated cyclooxygenase. This article is aimed at providing an overview about the often conflicting results concerning the mechanisms of action of aspirin and sodium salicylate. At present, there is no common agreement about the extent to which salicylate contributes to aspirin's anti-inflammatory properties, as well as there is still no final conclusion reached about the mechanisms of action of sodium salicylate. Several possible sites of action of salicylate have been suggested: It has been shown that in intact cells-but not in purified enzyme preparations-, sodium salicylate inhibits prostanoid biosynthesis. This effect seems to be prevented in the presence of high concentrations of arachidonic acid, which has been shown to interfere with inhibition by salicylate of cyclooxygenase-2-mediated prostanoid formation in vitro. Other possible sites of action that are not directly related to cyclooxygenase inhibition have been suggested based on observations made in vitro using high concentrations of aspirin and sodium salicylate. These effects target intracellular signaling mechanisms such as kinases, including the mitogen activated protein-kinases (MAPK) cascade. With the exception of reported salicylate-induced activation of p38 MAPK, observed effects are usually inhibitory. This may be one reason for the observation that, downstream to kinases, inhibitory effects of salicylates have been observed on several nuclear transcription factors, such as nuclear transcription factor kappa B (NF-kB) or activator protein 1 (AP-1). Several reports have also shown interference by salicylates with the expression of cyclooxygenase-2, which, depending on experimental models, can be observed as inhibitory but also stimulatory effects. Antioxidant properties of salicylates, adenosine release induced by sodium salicylate and aspirin-triggered lipoxin formation are additional mechanisms that may contribute to anti-inflammatory properties of aspirin and/or sodium salicylate. An additional focus of this review is the discussion of interactions between aspirin, sodium salicylate and other non-steroidal anti-inflammatory drugs (NSAIDs), which are of particular relevance in the gastro-intestinal and cardiovascular systems.

Interaction of cyclooxygenase-2 inhibitors and salicylate in gastric mucosal damage

The interactions of sodium salicylate and the selective cyclooxygenase-2 inhibitors N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide (NS-398) and 5.5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulfonyl)phenyl-2(5II)-furanone (DFU), dexamethasone and the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine methylester (L-NAME) were examined in ischaemia-reperfusion damage and adaptive protection in the rat stomach. Ischaemia-reperfusion damage was substantially aggravated by pretreatment with NS-398 (4 mg/kg), DFU (2 mg/kg), dexamethasone (1 mg/kg) or L-NAME (3 and 10 mg/kg). Salicylate (0.01-0.05 mg/kg) reversed the aggravating effect of NS-398, DFU and dexamethasone, while the effect of L-NAME was counteracted by L-arginine (twice 400 mg/kg) but not salicylate (0.05 or 10 mg/kg). Instillation of 20% ethanol prevented mucosal damage induced by 70% ethanol. This adaptive gastroprotection was abolished by pretreatment with NS-398 (1 mg/kg), DFU (0.2 mg/kg) or L-NAME (10 mg/kg). Salicylate (0.01-0.05 mg/kg) reversed the inhibition of protection by NS-398 and DFU, while the effect of L-NAME (10 mg/kg) was antagonized by L-arginine (100 mg/kg) but not salicylate (0.05 mg/kg). The precise mechanism of the functional antagonism between extremely low doses of salicylate and selective cyclooxygenase-2 inhibitors remains to be investigated.

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)

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.

Sodium salicylate does not prevent the inhibitory effect of indomethacin on thromboxane formation in human blood ex vivo

Thromboxane formation during spontaneous blood clotting as well as plasma levels of TXB2 and 6-keto-PGF1 alpha, the stable metabolites of TXA2 and prostacyclin, were measured by radioimmunoassay two hours after oral administration of indomethacin (25 mg), sodium salicylate (250 mg) and their combination to human volunteers. Indomethacin effectively suppressed the tremendous formation of TXB2 during blood clotting whereas sodium salicylate had only a slight inhibitory effect on TXB2 synthesis. The combination of indomethacin and sodium salicylate inhibited the formation of thromboxane even slightly more effectively than indomethacin alone. Plasma TXB2 level was decreased after the combination treatment but not after administration of either of the drugs alone. Plasma 6-keto-PGF1 alpha level was not changed by any of the treatments. The present study suggests that simultaneous oral administration of sodium salicylate together with indomethacin at a combination ratio of 10 to 1 does not significantly interfere with the inhibitory effects of indomethacin on thromboxane synthesis in human blood ex vivo.

The combined effects of sodium salicylate, aspirin and indomethacin on the metabolism of arachidonic acid in human platelets

The effects of acetylsalicylic acid (ASA, aspirin), indomethacin and sodium salicylate on the metabolism of exogenous 14C-arachidonic acid (AA) were studied in intact human platelets in vitro. ASA (100 microM) and indomethacin (1 and 10 microM) suppressed the metabolism of AA via the cyclo-oxygenase but had no effect on the lipoxygenase pathway. Sodium salicylate at 1 mM was ineffective whereas 2 mM salicylate significantly decreased the formation of TXB2 and HHT and increased that of other cyclo-oxygenase products without clearly affecting total cyclo-oxygenase activity. The formation of 12-HETE, the main metabolite of AA in human platelets, was decreased by 2 mM sodium salicylate as well as by the combination of 1 mM salicylate plus ASA or indomethacin. Pretreatment of platelets with sodium salicylate (1 or 2 mM) effectively prevented the inhibition of the cyclo-oxygenase by ASA (100 microM) but had no effect on the inhibition produced by indomethacin (1 or 10 microM). When sodium salicylate was added to the platelet-containing buffer after ASA or indomethacin it did not reverse the effects of these drugs on the cyclo-oxygenase. The present study suggests that sodium salicylate effectively prevents the inhibitory effect of ASA but not that of indomethacin on human platelet cyclo-oxygenase at the concentrations used. In addition, a high concentration of sodium salicylate (2 mM) may selectively inhibit the formation of TXB2 without clearly affecting total cyclo-oxygenase activity.