Topical delivery of salicylates

Salicylates have a long history of use for pain relief. Salicylic acid and methyl salicylate are among the widely used topical salicylates namely for keratolytic and anti-inflammatory actions, respectively. The current review summarises both passive and active strategies, including emerging technologies employed to enhance skin permeation of these two salicylate compounds. The formulation design of topical salicylic acid targets the drug retention in and on the skin based on the different indications including keratolytic, antibacterial and photoprotective actions, while the investigations of topical delivery strategies for methyl salicylate are limited. The pharmacokinetics and metabolisms of both salicylate compounds are discussed. The current overview and future perspectives of the topical delivery strategies are also highlighted for translational considerations of formulation designs.

Inactivation of cholinesterase induced by non-steroidal anti-inflammatory drugs with horseradish peroxidase: implication for Alzheimer's disease

AIMS

To clarify the mechanism of the protective effect of non-steroidal anti-inflammatory drugs (NSAIDs) on Alzheimer's disease, inactivation of cholinesterase (ChE) induced by NSAIDs was examined.

MAIN METHODS

Equine ChE and rat brain homogenate were incubated with NSAIDs and horseradish peroxidase (HRP) and H(2)O(2) (HRP-H(2)O(2)). ChE activity was measured by using 5,5'-dithiobis(nitrobenzoic acid). By using electron spin resonance, NSAID radicals induced by reaction with HRP-H(2)O(2) were detected in the presence of spin trap agents.

KEY FINDINGS

Equine ChE was inactivated by mefenamic acid with HRP-H(2)O(2). ChE activity in rat brain homogenate decreased dependent on the concentration of mefenamic acid in the presence of HRP-H(2)O(2). NSAIDs diclofenac, indomethacin, phenylbutazone, piroxicam and salicylic acid inactivated ChE. Oxygen radical scavengers did not prevent inactivation of ChE induced by mefenamic acid with HRP-H(2)O(2). However, spin trap agents 5,5-dimethyl-1-pyrroline-l-oxide and N-methyl-nitrosopropane, reduced glutathione and ascorbic acid strongly inhibited inactivation of ChE, indicating participation of mefenamic acid radicals. Fluorescent emission of ChE peaked at 400 nm, and the Vmax value of ChE changed during interaction of mefenamic acid with HRP-H(2)O(2), indicating that ChE may be inactivated through modification of tyrosine residues by mefenamic radicals.

SIGNIFICANCE

The protective effect of NSAIDs on Alzheimer's disease seems to occur through inactivation of ChE induced by NSAIDs radicals.

Searching for new NO-donor aspirin-like molecules: a new class of nitrooxy-acyl derivatives of salicylic acid

A new class of products in which the phenol group of salicylic acid is linked to alkanoyl moieties bearing nitrooxy functions has been synthesized and studied for their polyvalent actions. The products were stable in acid and neutral media, while they were hydrolyzed in human serum. Their half-lives were dependent upon the structure of alkanoyl moieties. The products showed anti-inflammatory activities similar to aspirin when tested in the carrageenan-induced paw edema assay in the rat. Interestingly, unlike aspirin, they showed reduced or no gastrotoxicity in a lesion model in rats at equimolar doses. A number of them were able to inhibit platelet aggregation induced by collagen in human platelet-rich plasma. All of the products were capable of relaxing rat aortic strips precontracted with phenylephrine in a concentration-dependent manner. Selected members of this new class of nonsteroidal anti-inflammatory drugs might represent possible safer alternatives to aspirin in different clinical settings.

Sex-dependent differences in the activities of acetylsalicylic acid-esterases in mouse kidneys

Acetylsalicylic acid (ASA), the most used drug worldwide, is hydrolyzed to salicylic acid and acetate by esterases present in tissues of several species including humans. Sex differences in drug metabolism by rodent liver are documented in the literature. In this paper we report a difference in the activities of the esterases (ASA-esterase I and II) in the kidneys of male and female mice. In this species there is no difference between males and females in liver ASA-esterases (ASA-esterase I: males 38.5 +/- 7.9 (N = 5) and females 31.6 +/- 7.6 (N = 5) nmol of salicylic acid formed min-1 mg protein-1, P > 0.05; ASA-esterase II: males 77.3 +/- 17.4 (N = 5) and females 61.4 +/- 15.1 (N = 5) nmol of salicylic acid formed min-1 mg protein-1, P > 0.05). However, in the kidneys males presented a much higher enzyme activity than females (ASA-esterase I: males 25.2 +/- 6.3 (N = 5) and females 6.8 +/- 0.6 (N = 5) nmol of salicylic acid formed min-1 mg protein-1, P < 0.0002; ASA-esterase II: males 79.8 +/- 10.1 (N = 5) and females 13.0 +/- 1.1 (N = 5) nmol of salicylic acid formed min-1 mg protein-1, P < 0.0001). The difference between sexes observed in mouse kidneys could serve as a model to study the molecular basis of this sex difference and also to determine the possible involvement of pituitary and gonadal hormones in this difference in ASA-esterase activities since these hormones control the sex differences in rodent liver enzyme activity.

Stability and pharmacokinetic studies of a new immunosuppressant, mycophenolate mofetil (RS-61443), in rats

Mycophenolate mofetil (MPM), a new immunosuppressant, is a morpholinoethyl ester of mycophenolic acid (MPA). The enzymatic and non-enzymatic hydrolysis was studied in an artificial digestive fluid, rat plasma, and tissue homogenates. MPM was chemically stable in the artificial digestive fluid. In rat tissue homogenates and plasma, MPM was rapidly hydrolysed to MPA. The conversion rate of MPM to MPA in various rat tissue homogenates was in the order of liver > kidney > plasma > small-intestine epithelial cells. After the intravenous injection of MPM at 16.7 mg kg-1, the terminal elimination half-life, t1/2 beta, was 4.74 +/- 0.33 (mean +/- SD)h, and the area under the plasma concentration versus time curve, AUC, was 48.78 +/- 6.01 micrograms h mL-1. After intraduodenal (ID) administration of MPM at 16.7 mg kg-1, t1/2 beta was 3.92 +/- 1.05 h, and the AUC was 38.08 +/- 8.30 micrograms h mL-1. The systemic availability of MPA after ID MPM dosing was 1.52 times higher than that after ID administration of MPA. This result supports the usefulness of MPM as an oral prodrug of MPA as a new oral immunosuppressant.

Enzymic hydrolysis of nicotinate esters: comparison between plasma and liver catalysis

1. The enzymic hydrolysis of a wide series of nicotinic acid esters was investigated using human and rat plasma, and purified hog liver carboxylesterase, and compared with previously published data from rat liver microsomes. Esterase activities were always found to obey Michaelis-Menten kinetics. 2. Rat liver microsomal and plasma enzyme velocities were six orders of magnitude smaller than those of purified hog liver carboxylesterase, and three orders smaller than human plasma activities, but the Km values were of the same magnitude. 3. The binding of nicotinate esters to human plasma esterases, and purified hog liver carboxylesterase, appears to depend mainly on hydrophobic and steric factors.

Facile hydrolysis of mebeverine in vitro and in vivo: negligible circulating concentrations of the drug after oral administration

The HPLC methods for the determination of plasma concentrations of the antispasmodic agent mebeverine (0.01-10 micrograms/mL) and its hydrolysis product veratric acid (0.1-50 micrograms/mL) are presented. Mebeverine was demonstrated to hydrolyze readily in fresh unbuffered human and rat plasma samples ex vivo. Hydrolysis in human plasma was completely inhibited in the presence of the esterase inhibitor physostigmine sulfate, at a concentration of 130 micrograms/mL. However, the inhibitor was only partially effective in blocking mebeverine hydrolysis in rat plasma. After oral administration of mebeverine.HCl (270 mg) to fasted human volunteers, measurable concentrations of the drug were not found in plasma. By contrast, the metabolite veratric acid achieved considerable concentrations (mean peak plasma concentration of 13.5 micrograms/mL at 40-80 min). After iv administration of mebeverine.HCl (2 mg) to rats, the drug was rapidly eliminated from plasma (mean half-life of 29 min) with simultaneous appearance of veratric acid (mean peak plasma concentration of 1.80 micrograms/mL at 15-30 min). However, after oral administration of the same dose, only traces of mebeverine were found in plasma, with the exception of one rat. Veratric acid again achieved considerable concentrations (mean peak plasma concentration of 0.90 micrograms/mL at 15 min-4 h). The results show that mebeverine undergoes rapid and extensive first-pass metabolism involving hydrolysis of the ester function, and that negligible circulating concentrations of the parent drug are found in humans.

Ibuprofen piconol hydrolysis in vitro in plasma, whole blood, and serum using different anticoagulants

Hydrolysis kinetics of ibuprofen piconol to ibuprofen were determined in vitro in plasma, whole blood, and serum. Varying initial concentrations of ibuprofen piconol with different anticoagulants (EDTA, heparin, citrate, or no anticoagulant) were used in determining the effects each had on the rate of ibuprofen piconol hydrolysis. Varying the initial concentration of ibuprofen piconol did not alter the hydrolysis half-life (concentration range from 50 to 200 micrograms/mL). The anticoagulant used altered the hydrolysis half-life. For plasma, the half-life was shortest when no anticoagulant was present (t 1/2 = 2.5 h) and longer with the presence of anticoagulants; for citrate, t 1/2 = 8.0 h, for heparin; t 1/2 = 15.5 h; and for EDTA, t 1/2 = 161.8 h. Red blood cell uptake of ibuprofen piconol was minimal and ranged from 0.4 to 4.1% over the ibuprofen piconol concentrations used in the study.

Aspirin hydrolyzing esterases from rat liver cytosol

Unlike most esterases, which are predominantly bound to the microsomal fraction, the enzymes hydrolyzing acetylsalicylic acid are present in an equal amount in the cytosol. Two soluble isozymes were purified to homogeneity from rat liver and characterized as serine esterases with a Mr of 35,000. Both had the wide substrate spectrum characteristic of enzymes active in detoxication. Both had a very low Km for acetylsalicylate. Three other cytoplasmic enzymes active with aspirin were observed but these differed in their high Mr (about 220,000) and their lack of reactivity with antibody to one of the homogeneous isozymes.

Aspirin augments alcohol in restricting brain growth in the neonatal rat

The purpose of this study was to determine whether the microencephaly in rats resulting from early postnatal alcohol exposure is altered by a concurrent administration of aspirin. Neonatal rats were artificially reared from postnatal day 4 to postnatal day 10, a period of the brain growth spurt in the rat that is similar to the third trimester of human brain development. The alcohol-treated groups received 6.6 g/kg/day of ethanol and either 0.0, 12.5, 25.0 or 50.0 mg/kg/day of aspirin in a milk solution. Control groups received either 0.0 (gastrostomy control), 12.5, 25.0 or 50.0 mg/kg/day of aspirin in a milk solution free of alcohol. Brainstem, cerebellum and total brain weights were measured on postnatal day 10. Alcohol alone significantly reduced the mean total brain weight, cerebellum and brainstem weight by 19.8%, 23.1% and 12.2%, respectively, relative to gastrostomy controls. A significant interaction between ethanol and aspirin was observed for total brain weight. The mean total brain weight of the group receiving both alcohol and 50 mg/kg/day aspirin was significantly lower than all other experimental groups and was reduced 29.5%, relative to gastrostomy controls. The highest dose of aspirin alone significantly reduced cerebellar weight, relative to gastrostomy controls but had no effect on brainstem or total brain weight.

Aspirin-induced gastric mucosal injury: lessons learned from animal models

This review of the mechanisms by which aspirin causes gastric mucosal damage points to the involvement of two potential mechanisms. Aspirin, which inhibits cyclooxygenase, is rapidly deacetylated to salicylate. Salicylate is toxic to cells and affects mucosal barrier function, reduces cytosolic adenosine triphosphate, stimulates sodium transport, and increases proton dissipation from surface epithelial cells. Cyclooxygenase inhibition makes the gastric mucosa more susceptible to injury, inhibits mucus and bicarbonate secretion, alters the physicochemical nature of mucus, stimulates fundic but not antral [3H]thymidine incorporation, and reduces epithelial surface hydrophobicity. No single mechanism seems to be involved. It is likely, instead, that the toxic effects of salicylate and the effect of cyclooxygenase inhibition work in concert to render the mucosa more susceptible to injury, resulting in mucosal damage.

Aspirin disposition in rats acutely intoxicated with CCl4

The profile of urinary salicylate metabolites was determined after an oral administration of acetylsalicylic acid (ASA) to: 1, control rats; 2, rats treated with CCl4 and 3, rats intoxicated with CCl4 and also pretreated with colchicine for 7 days. The following enzymatic activities were determined: liver and plasma ASA-esterase, liver UDP-glucuronyltransferase and liver aniline hydroxylase. The time course of plasma concentration of salicylates in similar groups were followed after the intraperitoneal administration of acetylsalicylic acid (ASA), salicylic acid (SA) or gentisic acid (GA). The animals acutely intoxicated with CCl4 showed a reduction in urinary excretion of glucuronates and an increased urinary excretion of gentisic and salicylic acids. The activities of plasma and liver ASA-esterases were significantly increased in CCl4-treated rats while the aniline hydroxylase was reduced and the UDP-glucuronyltransferase remained unchanged. The plasma half lives of salicylates were reduced in CCl4-treated rats regardless of the administered parent compound. Colchicine pre-treatment completely prevented the alterations produced by acute intoxication with CCl4. The heterogeneity of liver metabolic dysfunctions present in acute liver damage was evidenced. It is emphasized that the pharmacokinetic alterations produced by acute liver injury can be the result of complex factors that may involve changes in circulation, hepatic binding protein and other routes of elimination.

Parenteral aspirin and sodium salicylate are equally injurious to the rat gastric mucosa

The effects of parenteral aspirin (ASA) or sodium salicylate (SA) on the gastric mucosa were investigated in anesthetized pylorus-ligated rats 3 h after a bolus intravenous injection of ASA or SA, 150 mg/kg, or NaCl (control). Aspirin or SA produced similar extensive gross mucosal hemorrhagic lesions and similar microscopic damage in the presence of luminal acid (luminal pH 1.3 +/- 0.05). Neither ASA nor SA produced gastric mucosal injury with intragastric instillation of saline (luminal pH 3.7 +/- 0.5). Pretreatment for 1 h with luminal or subcutaneous 16,16-dimethyl prostaglandin E2 completely prevented the formation of red streaks in ASA-treated rats but not in SA-treated rats, although prostaglandin E2 pretreatment significantly reduced the gross lesion area in SA-treated rats (p less than 0.05). We conclude the following: (a) Intravenous SA is as damaging as intravenous ASA as long as luminal acid is present. (b) 16,16-Dimethyl prostaglandin E2 completely protected the gastric mucosa from injury by intravenous ASA, and to a lesser extent by intravenous SA. (c) In view of the damaging effects of SA on the gastric mucosa and the rapid conversion of ASA to SA, the mechanism of the gastric mucosal injury by intravenous ASA is much more complex than simple inhibition of endogenous prostaglandin synthesis.

Effect of simulated systemic administration of aspirin, salicylate, and indomethacin on amphibian gastric mucosa

The effects of 20 mM aspirin (ASA), 20 mM sodium salicylate (SA), or 10(-4) M indomethacin placed in the nutrient solution (N) to stimulate systemic administration were investigated at pHN 7.3 in Ussing-chambered amphibian gastric mucosae. In histamine-stimulated tissues, the initial rise and subsequent rapid fall in potential difference, rise in resistance, and inhibition of hydrogen ion (H+) secretion induced by SAN did not occur with ASAN unless hydrolysis of ASAN produced a SAN of greater than 3 mM. In metiamide-treated tissues, 20 mM SAN caused an immediate fall in potential difference and an increase in resistance; 2 mM SAN and 20 mM ASA produced similar qualitative electrical changes, but only those induced by ASA were reversible. IndomethacinN caused no significant changes in potential difference, resistance, or H+ secretion in histamine- or metiamide-treated tissues. Despite producing highly significant reductions in generation of prostaglandin E2, and prostaglanndin F2 alpha and 6-keto prostaglandin F1 alpha, ASAN and indomethacin caused no surface ulceration. Sodium salicylate placed in the nutrient solution caused only a small reduction in prostaglandin F2 alpha, without change in the other prostaglandins, and produced extensive edema in the lamina propria, histologically. We conclude the following: (a) The inhibition of H+ secretion and electrical changes caused by SAN in histamine-treated gastric fundus are not observed with ASAN unless there is hydrolysis to [SAN] greater than 3 mM. (b) Our data strongly implicate the SAN in ASAN-containing solutions as being responsible for the electrical effects and inhibition of H+ secretion. (c) There is no correlation in vitro between inhibition of prostaglandin synthesis and the electrical or morphologic changes produced by nutrient exposure to ASA, SA, or indomethacin.

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

When aspirin is administered by mouth in low doses, poor systemic bioavailability may contribute to its apparent dose-related "selective inhibition" of thromboxane A2 formation. Systemic bioavailability of orally administered aspirin is necessary to inhibit prostacyclin synthesis by systemic vascular endothelium, whereas cumulative inhibition of thromboxane A2 formation by platelets may occur in the presystemic (portal) circulation. We simultaneously administered unlabeled aspirin orally and deuterium-labeled aspirin intravenously in five healthy volunteers. This permitted an estimation of the bioavailability of an oral dose from the ratio of plasma drug concentration-time curves for the labeled and the unlabeled species. Systemic bioavailability ranged from 46 to 51 per cent of single oral doses of 20, 40, 325, and 1300 mg of aspirin. Bioavailability was similar after single-dose and long-term oral administration of 325 mg. Thromboxane B2 formation in serum ex vivo after oral administration of 20 mg of unlabeled aspirin was reduced 39 per cent before aspirin was detected in the systemic circulation. Furthermore, incubation of simulated peak plasma aspirin concentrations in whole blood in vitro underestimated the inhibition of thromboxane B2 ex vivo after oral administration of 20 or 40 mg of unlabeled aspirin. These data are consistent with presystemic inhibition of platelets by aspirin and suggest that biochemical "selectivity" might be enhanced by slow administration of very low doses of aspirin, thereby optimizing conditions for cumulative, presystemic acetylation of platelet cyclooxygenase and inhibition of thromboxane formation.

The metabolism of aspirin in rats; localization, absorption, distribution and excretion

By the use of acetylsalicylic acid (aspirin) 14C-labelled in either the acetyl or the carboxyl group, the metabolic pathway and the degree of degradation of the substance were studied. The change in aspirin concentration and the rate of degradation occurring in major tissues and organs after oral administration was measured by radioactivity techniques. The degree of degradation for the period 10-30 minutes was found to be about 38% in the stomach wall, 64% in the liver and 86% in the lung, and less than 10% in the circulating portion of aspirin itself in blood, under conditions of equilibrium concentration of substrate. A technique measuring 14CO2 in expired air and using 14C-acetyl aspirin allowed for determination of the kinetics of the transformation of this compound into salicylic acid. The effective period for aspirin for unstrained and unanesthetized rats given orally was determined to be 90 min. The metabolic fates of the two kinds of 14C-labelled aspirin given orally were found to be very different and characteristic by counting and autoradiographic techniques. The distribution of [carboxyl-14C] aspirin was rather uniform, but [acetyl-14C] aspirin preferentially accumulated in the bone cortex portion.

High-performance liquid chromatographic determination of aspirin and its metabolites in plasma and urine

A simple quantitative method for the rapid determination of aspirin and its metabolites, salicylic acid, salicyluric acid, and gentisic acid, in plasma and urine using o-toluic and o-anisic acids, respectively, as internal standards was developed. Plasma proteins were precipitated by the addition of acetonitrile and, after centrifugation, the supernatant fluid was injected directly onto a reverse-phase column. The mobile phase consisted of an isocratic mixture of water, methanol, and glacial acetic acid (64:25:1, v/v/v) and the separated components were detected at 238 nm using a UV detector. Concentrations greater than or equal to 0.5 microgram/ml could be quantitated for aspirin or its metabolites in plasma. The peak heights and peak height ratios to the internal standard, o-toluic acid, were linear for the concentration range of 0.5-200 micrograms/ml. The aspirin metabolites in urine were isolated by extracting the acidified urine with either and then reextracting the material into an aqueous buffer solution at pH 7.0. Twenty microliters of the buffer extract was directly injected onto the column. The separated components were detected and quantitated at 305 nm. Concentrations greater than or equal to 5 micrograms/ml of salicyluric acid, salicylic acid, and gentisic acid could be determined accurately. The peak heights and peak height ratios to the internal standard, o-anisic acid, were found to be linear for the concentration range of 5-200 micrograms/ml in urine.

Stability of aspirin in different media

Aspirin rapidly hydrolyzes in various aqueous, organic, and biological media. The purpose of this investigation was to study the decomposition of aspirin in the media that comes in contact with it during analysis in biological fluids for pharmacokinetic studies. These media included water, water-polyethylene glycol 400, water-methanol-acetic acid, phosphate buffer, freshly drawn blood and plasma from control rats and rats deprived of water for 36 hr, and blood precipitated with acetonitrile. Studies were also conducted to determine the decomposition as a function of temperature and pH. Of the various solvent systems studied, aspirin was found most stable in water-polyethylene glycol (4:1, v/v),which provides an excellent medium for preparation of intravenous dosage forms. Phosphate buffer showed significant catalysis of aspirin hydrolysis. A more than fivefold increase in the hydrolysis of aspirin was noted when the temperature was raised to 37 degrees from 22.5 degrees. The hydrolysis of aspirin in rat blood was 13 times faster than that in plasma, with an average half-life in blood of approximately 13 min. This creates significant problems in aspirin disposition kinetic studies. Mixing the blood sample immediately after collection with twice the volume of acetonitrile and thn en centrifuging gives a plasma-acetonitrile mixture in which no lysis of blood cells is observed.

Distribution of the acetyl compared with the salicyl moiety of acetylsalicylic acid. Acetylation of macromolecules in organs wherein side-effects are manifest

The distribution in rats of the acetyl group of aspirin has been compared with that of the salicyl moiety with the objective of establishing if: (1) there are differences in their biodisposition which might be important in the development of side- or therapeutic effects of aspirin, and (2) the range of organs and biomolecules therein which are acetylated by aspirin. Using whole-body autoradiography and liquid scintillation counting techniques it was found that the acetyl group of 3H- or 14C-acetyl-labelled aspirin became bound to a wide variety of proteins, glycoproteins and lipids of the glandular and non-glandular region of the stomach, kidney, liver and to a lesser extent bone marrow, i.e. organs in which side-effects are frequently encountered. It is suggested that: (1) the acetylation of biomolecules may be a major factor in the development of side-effects in these organs, and (2) in addition to acetylation of prostaglandin synthetase, the acetylation of enzymes and other biomolecules may have a much wider bearing on the biochemical changes underlying the development of these side-effects. Acetylation of the protein/macromolecular components was especially pronounced in inflamed (c.f. control) hindpaws of carrageenan-injected rats. This could be a result of acetylation of the drug-carrier protein, albumin, and other proteins carried into inflamed tissues and this acetylation could have marked consequences for the functions of these proteins.

Determination of acetylsalicylic acid and metabolites in biological fluids by high-performance liquid chromatography

A new method has been developed for the determination of acetylsalicylic acid, salicylic acid, salicyluric acid and gentisic acid in plasma, urine and tissue homogenates by simple extraction with ethyl acetate, evaporation and redissolution and measuring by high-performance liquid chromatography. Linearity, reproducibility and recovery were determined. Experiments were carried out to investigate the decomposition of acetylsalicylic acid in plasma with fluoride at different temperatures. The method has been used for pharmacokinetic experiments and an example is given.

Disposition of 2,3-dihydro-8-[2-hydroxy-3-[4-[1-oxo-3-(3,4, 5-trimethoxyphenyl)-2-propenyl]-1-piperazinyl]-propoxy]-1, 4-benzodioxin-5-carboxylic acid, isopentyl ester (TPBE) in rat and dog, and its hydrolysis in vitro in rat, dog and man

1. 14C-Labelled 2,3-dihydro-8-[2-hydroxy-3-[4-[1-oxo-3-(3,4, 5-trimethoxyphenyl)-2-propenyl]-1-piperazinyl]propoxy]-1, 4-benzodioxin-5-carboxylic acid, isopentyl ester (TPBE) was administered orally and intravenously to rats and dogs and excretion in urine and faeces studied. Large amounts of radioactivity were present in faeces after i.v. drug administration, indicating that biliary excretion was important. 2. Biliary excretion in bile-duct cannulated rats and dogs showed that within one hour after i.v. dosage, greater than 50% dose was excreted in the bile of both species. Much lower amounts of radioactivity were excreted in bile after oral administration, indicating that absorption was incomplete. 3. T.l.c. of urine, bile and faeces showed that the hydrolysis product of TPBE was the major metabolite in urine and bile of the rat, but was less predominant in dog. 4. Incubation of TPBE in rat whole blood, and with homogenates of liver and small intestine, demonstrated hydrolysis of the drug. Hydrolysis by small intestine and colon contents was low. In the dog, only liver homogenates were capable of extensive hydrolysis of the drug. Hydrolysis also occurred in human blood in vitro; hydrolysis was most rapid in blood of rat then man and finally dog. 5. Experiments in vitro indicate that hydrolysis of TPBE in dog in vivo is likely to be mainly hepatic, whereas in rat hydrolysis in vivo is likely to be both hepatic and extrahepatic (blood and intestines). Results from rat, dog and man indicate that man is likely to be similar to the rat in hydrolysis of TPBE.

Improved delivery through biological membranes VIII: Design, synthesis, and in vivo testing of true prodrugs of aspirin

Novel activated ester-type prodrugs of aspirin were designed and synthesized. The methylthiomethyl, methylsulfinymethyl, and methylsulfonylmethyl esters of aspirin (acetylsalicylic acid) were cleaved in vitro in plasma to form aspirin rather than the corresponding salicylates. In vitro studies using dogs indicated that at least one aspirin derivative, methylsulfinylmethyl-2-acetoxybenzoate, is a true aspirin prodrug since aspirin was detected in the blood after prodrug administration.

Hydrolysis of an orally active platelet inhibitory prostanoid amide in the plasma of several species

The prostanoid 3-oxa-4,5,6-trinor-3,7-inter-m-phenylene-PGE1-amide (OI-PGE1-amide) has a prolonged duration of oral platelet aggregation inhibitory activity when compared to the parent free acid (OI-PGE1) in the rat. When incubated in rat plasma at 1 microgram/ml for 30 seconds prior to addition of ADP, OI-PGE1-amide inhibits in vitro rat platelet aggregation approximately 50%. OI-PGE1 inhibits at 1 ng/ml. Inhibition of platelet aggregation by plasma incubated with OI-PGE1-amide (1 microgram/ml) increases with time and the rate of this increase differs with species. Incubation of OI-PGE1 in plasma does not result in an increase of platelet inhibitory activity with time. The increase of platelet inhibitory activity was assumed to indicate hydrolysis of OI-PGE1-amide to the more active OI-PGE1. A compound, different from OI-PGE1-amide, was isolated by an ion exchange/silica gel separation sequence from an incubation of OI-PGE1-amide in rat plasma. It had potent platelet aggregation inhibitory activity. This material was shown to be OI-PGE1 by thin-layer chromatography, gas chromatography and mass spectral analysis. Studies with [3H]-OI-PGE1-amide confirmed the formation of OI-PGE1 in plasma incubations. Amide hydrolytic activity was significantly different between species, the rank order being: rat greater than guine pig greater than monkey = human greater than dog. This relationship corresponded with that determined by measuring the increase in platelet inhibitory activity with time in plasma incubations of OI-PGE1-amide reported above. Present data indicate that (a) OI-PGE1-amide is hydrolyzed to the parent acid by plasma enzymes of several species and (b) hydrolytic activity of plasma varies widely between species.

Effect of other drugs and chemicals on the degradation of aspirin in vitro: possible extrapolation to in vivo metabolism of aspirin

To assess the possible influence of other drugs and chemicals on the metabolic degradation of aspirin in man, their effect on the serum aspirin esterase activity was determined in vitro. The activation or inhibition of the enzyme as observed with these compounds suggest the possibility that simultaneous ingestion of these drugs with aspirin may influence the pharmacology and toxicity of the analgesic.

Acetylsalicylic acid hydrolase of gastric mucosa

Acetylsalicylic acid hydrolase activity of rabbit fundic gastric mucosa has been isolated from the soluble 100,000 X g supernate. The enzymatic activity was partially purified by ammonium sulfate precipitation. The Km for acetylsalicylate was 2 mM and pH optimum was 8.6. The activity was insensitive to ionic strength, slightly inhibited by inclusion of 100 mM Cl-, and demonstrated no requirement for Ca2+ or Mg2+. Acetylsalicylic acid esterase was markedly inhibited by sodium cholate and sodium dodecyl sulfate. The enzyme was insensitive to sulfhydryl reagents with the exception of p-chloromercuribenzenesulfonic acid, which markedly inhibited the enzyme. Diisopropyl fluorophosphate (DFP) inhibited enzymatic activity with a Ki of 9 X 10(-9)M. Eserine was also inhibitory with a Ki of 0.25 mM. Inhibition by DFP at low concentration and by eserine at millimolar concentrations suggests that this enzyme is related to the group of aliphatic esterases. Identification of potent inhibitors will enable studies to define the role of this enzyme with the use of experimental preparations in which systemic toxicity can be avoided.

Serum aspirin esterase activity in women with habitual aspirin intake

A method for the determination of aspirin esterase activity in serum is described. Sera from 59 pregnant women who were habitual aspirin users were found to have a mean enzyme activity value statistically lower than those of 68 non-pregnant women controls or of 12 pregnant women controls who were either occasional users of the drug or were non-users. The distribution of enzyme activity in the experimental group was also significantly different from that of the control group. It is postulated that the low enzyme activity may further aggravate the injurious effects of high intake of aspirin.

Comparative metabolism of benorylate and an equivalent mixture of aspirin and paracetamol in neonate and adult rabbits

1. Benorylate was well absorbed in rabbits, but more slowly than an equimolar mixture of aspirin and paracetamol. 2. Benorylate was extensively hydrolysed and converted to the typical metabolites of aspirin and paracetamol by both neonate and mature rabbits. 3. Absorption of either aspirin-paracetamol or benorylate was slower in neonate rabbits than in adult rabbits. 4. The excretion rate in adult rabbits was faster, for both aspirin and paracetamol metabolites, than in neonate rabbits.

A simultaneous determination of acetylsalicylic acid, salicylic acid and salicylamide in plasma by gas liquid chromatography

A novel method for the simultaneous determination of acetylsalicylic acid, salicylic acid and salicylamide in biological fluids by gas liquid chromatography is described. The assay has been used to determine the plasma concentration of salicylates in 10 volunteers after oral ingestion of three commercially available aspirin-containing formulations. No difficulty was encountered in determining low concentrations of acetylsalicylic acid in the presence of higher concentrations of salicylic acid. The in vivo plasma half life of acetylsalicylic acid in man was found to be 15.5 min.

The hydrolysis of acetylsalicylic acid by liver microsomes

Pretreatment of rats and guinea-pigs with phenobarbitone or phenylbutazone leads to a decrease in the rate of hydrolysis of acetylsalicylic acid in vitro by liver microsomes, treatment with phenacetin does not.