Aspirin, salicylate and prostaglandins

Safety Assessment of Salicylic Acid, Butyloctyl Salicylate, Calcium Salicylate, C12–15 Alkyl Salicylate, Capryloyl Salicylic Acid, Hexyldodecyl Salicylate, Isocetyl Salicylate, Isodecyl Salicylate, Magnesium Salicylate, MEA-Salicylate, Ethylhexyl Salicylate, Potassium Salicylate, Methyl Salicylate, Myristyl Salicylate, Sodium Salicylate, TEA-Salicylate, and Tridecyl Salicylate

Salicylic Acid is an aromatic acid used in cosmetic formulations as a denaturant, hair-conditioning agent, and skin-conditioning agent—miscellaneous in a wide range of cosmetic products at concentrations ranging from 0.0008% to 3%. The Calcium, Magnesium, and MEA salts are preservatives, and Potassium Salicylate is a cosmetic biocide and preservative, not currently in use. Sodium Salicylate is used as a denaturant and preservative (0.09% to 2%). The TEA salt of Salicylic Acid is used as an ultraviolet (UV) light absorber (0.0001% to 0.75%). Several Salicylic Acid esters are used as skin conditioning agents—miscellaneous (Capryloyl, 0.1% to 1%; C12–15 Alkyl, no current use; Isocetyl, 3% to 5%; Isodecyl, no current use; and Tridecyl, no current use). Butyloctyl Salicylate (0.5% to 5%) and Hexyldodecyl Salicylate (no current use) are hair-conditioning agents and skin-conditioning agents—miscellaneous. Ethylhexyl Salicylate (formerly known as Octyl Salicylate) is used as a fragrance ingredient, sunscreen agent, and UV light absorber (0.001% to 8%), and Methyl Salicylate is used as a denaturant and flavoring agent (0.0001% to 0.6%). Myristyl Salicylate has no reported function. Isodecyl Salicylate is used in three formulations, but no concentration of use information was reported. Salicylates are absorbed percutaneously. Around 10% of applied salicylates can remain in the skin. Salicylic Acid is reported to enhance percutaneous penetration of some agents (e.g., vitamin A), but not others (e.g., hydrocortisone). Little acute toxicity (LD50 in rats; >2 g/kg) via a dermal exposure route is seen for Salicylic Acid, Methyl Salicylate, Tridecyl Salicylate, and Butyloctyl Salicylate. Short-term oral, inhalation, and parenteral exposures to salicylates sufficient to produce high blood concentrations are associated primarily with liver and kidney damage. Subchronic dermal exposures to undiluted Methyl Salicylate were associated with kidney damage. Chronic oral exposure to Methyl Salicylate produced bone lesions as a function of the level of exposure in 2-year rat studies; liver damage was seen in dogs exposed to 0.15 g/kg/day in one study; kidney and liver weight increases in another study at the same exposure; but no liver or kidney abnormalities in a study at 0.167 g/kg/day. Applications of Isodecyl, Tridecyl, and Butyloctyl Salicylate were not irritating to rabbit skin, whereas undiluted Ethylhexyl Salicylate produced minimal to mild irritation. Methyl Salicylate at a 1% concentration with a 70% ethanol vehicle were irritating, whereas a 6% concentration in polyethylene glycol produced little or no irritation. Isodecyl Salicylate, Methyl Salicylate, Ethylhexyl (Octyl) Salicylate, Tridecyl Salicylate, and Butyloctyl Salicylate were not ocular irritants. Although Salicylic Acid at a concentration of 20% in acetone was positive in the local lymph node assay, a concentration of 20% in acetone/olive oil was not. Methyl Salicylate was negative at concentrations up to 25% in this assay, independent of vehicle. Maximization tests of Methyl Salicylate, Ethylhexyl Salicylate, and Butyloctyl Salicylate produced no sensitization in guinea pigs. Neither Salicylic Acid nor Tridecyl Salicylate were photosensitizers. Salicylic Acid, produced when aspirin is rapidly hydrolyzed after absorption from the gut, was reported to be the causative agent in aspirin teratogenesis in animals. Dermal exposures to Methyl Salicylate, oral exposures to Salicylic Acid, Sodium Salicylate, and Methyl Salicylate, and parenteral exposures to Salicylic Acid, Sodium Salicylate, and Methyl Salicylate are all associated with reproductive and developmental toxicity as a function of blood levels reached as a result of exposure. An exposure assessment of a representative cosmetic product used on a daily basis estimated that the exposure from the cosmetic product would be only 20% of the level seen with ingestion of a “baby” aspirin (81 mg) on a daily basis. Studies of the genotoxic potential of Salicylic Acid, Sodium Salicylate, Isodecyl Salicylate, Methyl Salicylate, Ethylhexyl (Octyl) Salicylate, Tridecyl Salicylate, and Butyloctyl Salicylate were generally negative. Methyl Salicylate, in a mouse skin-painting study, did not induce neoplasms. Likewise, Methyl Salicylate was negative in a mouse pulmonary tumor system. In clinical tests, Salicylic Acid (2%) produced minimal cumulative irritation and slight or no irritation(1.5%); TEA-Salicylate (8%) produced no irritation; Methyl Salicylate (>12%) produced pain and erythema, a 1% aerosol produced erythema, but an 8% solution was not irritating; Ethylhexyl Salicylate (4%) and undiluted Tridecyl Salicylate produced no irritation. In atopic patients, Methyl Salicylate caused irritation as a function of concentration (no irritation at concentrations of 15% or less). In normal skin, Salicylic Acid, Methyl Salicylate, and Ethylhexyl (Octyl) Salicylate are not sensitizers. Salicylic Acid is not a photosensitizer, nor is it phototoxic. Salicylic Acid and Ethylhexyl Salicylate are low-level photoprotective agents. Salicylic Acid is well-documented to have keratolytic action on normal human skin. Because of the possible use of these ingredients as exfoliating agents, a concern exists that repeated use may effectively increase exposure of the dermis and epidermis to UV radiation. It was concluded that the prudent course of action would be to advise the cosmetics industry that there is a risk of increased UV radiation damage with the use of any exfoliant, including Salicylic Acid and the listed salicylates, and that steps need to be taken to formulate cosmetic products with these ingredients as exfoliating agents so as not to increase sun sensitivity, or when increased sun sensitivity would be expected, to include directions for the daily use of sun protection. The available data were not sufficient to establish a limit on concentration of these ingredients, or to identify the minimum pH of formulations containing these ingredients, such that no skin irritation would occur, but it was recognized that it is possible to formulate cosmetic products in a way such that significant irritation would not be likely, and it was concluded that the cosmetics industry should formulate products containing these ingredients so as to be nonirritating. Although simultaneous use of several products containing Salicylic Acid could produce exposures greater than would be seen with use of baby aspirin (an exposure generally considered to not present a reproductive or developmental toxicity risk), it was not considered likely that consumers would simultaneously use multiple cosmetic products containing Salicylic Acid. Based on the available information, the Cosmetic Ingredient Review Expert Panel reached the conclusion that these ingredients are safe as used when formulated to avoid skin irritation and when formulated to avoid increasing the skin's sun sensitivity, or, when increased sun sensitivity would be expected, directions for use include the daily use of sun protection.

HPLC analysis of in vivo intestinal absorption and oxidative metabolism of salicylic acid in the rat

In vivo absorption and oxidative metabolism of salicylic acid in rat small intestine was studied by luminal perfusion experiment. Perfusion through the lumen of proximal jejunum with isotonic medium containing 250 μm sodium salicylate was carried out. Absorption of salicylate was measured by a validated HPLC-DAD method which was evaluated for a number of validation characteristics (specificity, repeatability and intermediate precision, limit of detection, limit of quantification, linearity and accuracy). The method was linear over the concentration range 0.5-50 μg/mL. After liquid-liquid extraction of the perfusion samples oxidative biotransformation of salicylate was also investigated by HPLC-MS. The method was linear over the concentration range 0.25-5.0 μg/mL. Two hydroxylated metabolites of salicylic acid (2,5-dihydroxybenzoic acid and 2,3-dihydroxybenzoic acid) were detected and identified. The mean recovery of extraction was 72.4% for 2,3-DHB, 72.5% for 2,5-DHB and 50.1% for salicylic acid, respectively. The methods were successfully applied to investigate jejunal absorption and oxidative metabolism of sodium salicylate in experimental animals. The methods provide analytical background for further metabolic studies of salycilates under modified physiological conditions.

Might salicylate exert benefits against childhood cancer?

Childhood cancers are a broad range of diseases. Research on the chemopreventive potential of non-steroidal anti-inflammatory drugs, such as aspirin (acetylsalicylate) has yet to be fully directed towards childhood cancers. A prima facie hypothesis on salicylate and childhood cancer would therefore be based on several factors. Firstly, salicylate inhibits the production of inflammatory prostaglandins, which have been shown to stimulate the growth of cancer cells. Secondly, salicylate inhibits the growth of cancer cells in pre-clinical models. Thirdly, salicylate is a natural component of fruits and vegetables so it is consumed within the diet. Further research, of which some possibilities are identified, is recommended.

Is aspirin a prodrug for antioxidant and cytokine-modulating oxymetabolites?

Aspirin and salicylate are transformed by stimulated human polymorphonuclear leucocytes (PMN), likely to be found at inflammatory sites, into both 2,3- and 2,5-dihydroxybenzoates (DHB). These DHB inhibit both the production of hydrogen peroxide by stimulated human PMN and prostaglandin (PG) E2 by activated rat macrophages. In contrast, DHB stimulated production of interleukin (IL)-1 and tumour necrosis factor (TNF) but inhibited IL-6 production by rat macrophages. These effects were probably a consequence of PGE2 inhibition. Gentisate (2,5-DHB) and homogentisate (a tyrosine metabolite) inhibited the lymphoproliferative action of IL-1. Some related phenols, e.g. 5-aminosalicylate, inhibited H2O2 production but had little effect on PGE2 production. These findings suggest that the local synthesis of DHB may contribute to the overall anti-inflammatory activity of salicylate, which (unlike aspirin) has little direct effect on PG production.

The effect of fosfosal and acetylsalicylic acid on leukocyte migration and PGE2 concentration in experimentally induced acute inflammation

The effect of fosfosal, a non-acetylated salicylic acid derivative, on the content of prostaglandin E2 (PGE2) and the migration of polymorphonuclear leukocytes in inflammatory exudates induced by s.c. implantation of 0.5% carrageenan soaked sponges in rats has been determined. Fosfosal, which does not inhibit PG synthesis in vitro, is capable of reducing, in a dose-dependent manner, the PGE2 content of the exudates, with a maximum reduction of 50-60% at a total dose of 100 mg/kg i.p. Acetylsalicylic acid was slightly more potent (68% reduction, 2 x 50 mg/kg i.p.). Six hours after fosfosal administration, salicylic acid, the principal metabolite of fosfosal, accumulated in the exudates at concentrations of about 100 micrograms/ml. These concentrations were sufficient to inhibit PG synthetase activity in vitro. Neither fosfosal nor acetylsalicyclic acid affected polymorphonuclear leukocyte migration at doses which significantly reduced the concentrations of PGE2. Indomethacin, used as reference, reduced leukocyte migration by 28 and 45% at a dose of 1 and 10 mg/kg i.p. respectively. The results indicate that fosfosal, in spite of its lack of effect on PG biosynthesis in vitro, exerts an effect on the inflammatory locus in vivo which may account, at least in part, for its anti-inflammatory activity. Moreover, our results confirm that the inhibition of PG synthesis and leukocyte migration are mediated by different mechanisms.

Pharmacokinetics of aspirin and salicylate in relation to inhibition of arachidonate cyclooxygenase and antiinflammatory activity

Among the nonsteroid antiinflammatory drugs there is generally a close correlation between the potency of their inhibition of arachidonate cyclooxygenase, and thus prostaglandin production, and their antiinflammatory activity. One anomaly in this generalization is that whereas aspirin and salicylate are equipotent as antiinflammatory agents, salicylate is less active than aspirin in inhibiting prostaglandin production in vitro. Using rats, we have now measured the concentrations of aspirin and salicylate in plasma and in inflammatory exudates after their oral administration and determined their effects on thromboxane B2 production in clotting blood and prostaglandin (PG) E2 concentrations in the exudates. We have also investigated the effects of both drugs, at concentrations achieved in the exudates, on PGE2 production by nonproliferative explants of acutely inflamed tissues. Aspirin is rapidly metabolized, resulting in peak concentrations of salicylate in the plasma and exudate that exceeded peak concentrations of aspirin by 30- to 50-fold. Furthermore, concentrations of aspirin rapidly declined, whereas high concentrations of salicylate persisted in the plasma and in the exudate for up to 6 hr after a single administration of aspirin. Both drugs reduced PGE2 concentrations in inflammatory exudates by 50-70%, but aspirin was considerably more potent than salicylate in inhibiting thromboxane B2 production in clotting blood. The concentration of salicylate found in inflammatory exudates 6 hr after the administration of aspirin was sufficient to reduce PGE2 production in explants by more than 50%. We conclude that the antiinflammatory action of both drugs depends on the inhibition of PGE2 synthesis by salicylate.

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)

Effect of choline magnesium trisalicylate on prostacyclin production by isolated vascular tissue of the rat

Choline Magnesium Trisalicylate (Trilisate), in therapeutic concentrations of 5, 10, 15 and 30 mg/100 ml, did not significantly affect production of prostacyclin-like (PGI2) substance by rat aortic tissue in vitro. The ED50 for inhibition of aorta PGI2-like substance production by Trilisate was 1,200 mg/100 ml. This is approximately 40 times the maximum therapeutic blood concentration achieved in humans. Choline or Magnesium salicylate produced slight but insignificant inhibition of PGI2-like substance production by rat aortic tissue in vitro. The ED50 for ibuprofen (Motrin) for inhibition of PGI2-like production of rat aortic rings was 0.65-0.92 mg/100 ml. Injection of Choline Magnesium Trisalicylate into rats (124, 250, 500 mg/kg I.P.) did not affect the normal production of PGI2-like substance of aortic tissue obtained one hour after in vivo treatment. These results suggest this anti-inflammatory salicylate does not adversely affect PGI2-like production by blood vessels, in concentrations associated with therapeutic effects in man.

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

Salicylic acid (SA), a weak inhibitor of the prostaglandin endoperoxide synthetase or fatty acid cyclooxygenase enzyme, is known to prevent irreversible enzyme inhibition by acetylsalicylic acid (ASA). The interaction of arachidonic acid with ferrous sulfate was used as a model to study the reaction of the fatty acid with the postulated enzymic cationic binding site on Fe2+-heme. SA was as potent as ASA in inhibiting the cooxygenation of arachidonic acid and ferrous sulfate. The results suggests that SA could complete effectively for the enzyme cationic site with ASA. Thus SA may block ASA acetylation of the cyclooxygenase by preventing ASA from binding to this site.

Lipoxygenase products and the polymorphonuclear leucocyte

Polymorphonuclear leucocytes (PMNs), when exposed to the calcium ionophore A23178, release into the supernatant a substance that causes the aggregation and chemokinesis of fresh PMN suspensions. Release of these activities is inhibited by preincubation with drugs known to inhibit lipoxygenase pathways of arachidonic acid metabolism but is unaffected by cyclooxygenase inhibitors. The substance responsible for these activities has been identified as leukotriene B and this compound has been shown to be a potent chemokinetic and aggregatory agent for PMNs over the range 10 pg to 5 ng ml-1.