Improved method for the determination of aspirin and its metabolites in biological fluids by high-performance liquid chromatography: applications to human and animal studies

HPLC study on Fenton-reaction initiated oxidation of salicylic acid. Biological relevance of the reaction in intestinal biotransformation of salicylic acid

Fenton-reaction initiated in vitro oxidation and in vivo oxidative biotransformation of salicylic acid was investigated by HPLC-UV-Vis method. By means of the developed high performance liquid chromatography (HPLC) method salicylic acid, catechol, and all the possible monohydroxylated derivatives of salicylic acid can be separated. Fenton oxidations were performed in acidic medium (pH 3.0) with two reagent molar ratios: (1) salicylic acid: iron: hydrogen peroxide 1:3:1 and (2) 1:0.3:1. The incubation samples were analysed at different time points of the reactions. The biological effect of elevated reactive oxygen species concentration on the intestinal metabolism of salicylic acid was investigated by an experimental diabetic rat model. HPLC-MS analysis of the in vitro samples revealed presence of 2,3- and 2,5-dihydroxybenzoic acids. The results give evidence for nonenzyme catalysed intestinal hydroxylation of xenobiotics.

Oxidation of Hydroxy- and Dihydroxybenzoic Acids Under the Udenfriend's Conditions. An HPLC Study

Background:

Non-enzymatic hydroxylation of aromatic compounds to the respective phenolic derivatives is a possible metabolic pathway of xenobiotics. The formed metabolites can undergo consecutive oxidative reactions with free radicals to form potential toxic molecules.

Objective:

Development of HPLC methods to separate, identify and quantitate the main products formed from salicylic acid, 2,3-dihydroxybenzoic acid and 2,5-dihydroxybenzoic acid under in vitro hydroxylation conditions (Udenfriend's system).

Method:

An RP-HPLC-UV-Vis method was developed to separate salicylic acid and isomeric dihydroxybenzoic acids formed in the Udenfriend's system. Confirmation of structures of the oxidized products of salicylic acid, 2,3-dihydroxybenzoic acid and 2,5-dihydroxybenzoic acid was performed by HPLC-ESI-MS/MS method.

Results:

The HPLC-UV-Vis method was evaluated for a number of validation characteristics (selectivity, repeatability and intermediate precision, LOD, LOQ and calibration range). It was found that oxidation of salicylic acid resulted in the formation of 2,3- and 2,5-dihydroxybenzoic acids. Furthermore, the hydroxylated metabolites can be further metabolized under the Udenfriend’s conditions.

Conclusion:

The results give evidence for possible involvement of the oxidized metabolites of salicylic acid in the development of biological action of salicylates at the site of inflammation, where high hydroxyl radical level can be detected.

Sol-gel approach for extracting highly versatile aspirin and its metabolites using MISPE followed by GC-MS/MS analysis

AIM

Aspirin is known to be a salicylate drug widely used as an analgesic, antipyretic and anti-inflammatory drug.

METHODOLOGY

Sol-gel based nanosized molecularly imprinted polymer (nMIP) has been synthesized for extraction of aspirin and its metabolites in urine followed by GC-MS/MS analysis.

RESULTS

Binding affinity of nMIP and nonimprinted polymer was found to be in the range of 70-95% and 29-45%, respectively. LOD and LOQ of aspirin and its metabolites were found to be in the range of 0.63-2.4 ng/ml and 2.07-7.68 ng/ml, respectively.

CONCLUSION

The developed method was found to be applicable for routine analysis of aspirin and its metabolites in biological samples.

HSP-72 accelerated expression in mononuclear cells induced in vivo by acetyl salicylic acid can be reproduced in vitro when combined with H2O2

Background

Among NSAIDs acetyl salicylic acid remains as a valuable tool because of the variety of benefic prophylactic and therapeutic effects. Nevertheless, the molecular bases for these responses have not been complete understood. We explored the effect of acetyl salicylic acid on the heat shock response.

Results

Peripheral blood mononuclear cells from rats challenged with acetyl salicylic acid presented a faster kinetics of expression of HSP-72 messenger RNA and protein in response to in vitro heat shock. This effect reaches its maximum 2 h after treatment and disappeared after 5 h. On isolated peripheral blood mononuclear cells from untreated rats, incubation with acetyl salicylic acid was ineffective to produce priming, but this effect was mimicked when the cells were incubated with the combination of H₂O₂+ ASA.

Conclusions

Administration of acetyl salicylic acid to rats alters HSP-72 expression mechanism in a way that it becomes more efficient in response to in vitro heat shock. The fact that in vitro acetyl salicylic acid alone did not induce this priming effect implies that in vivo other signals are required. Priming could be reproduces in vitro with the combination of acetyl salicylic acid+H₂O₂.

Review of HPLC methods and HPLC methods with mass spectrometric detection for direct determination of aspirin with its metabolite(s) in various biological matrices

Aspirin, the most widely used drug in the world, has been known to mankind for over a century. It is not only the pharmacologically active entity, but is also biotransformed into a major metabolite, i.e. salicylic acid, which also exhibits similar pharmacologic/pharmacodynamic properties. Hence it is necessary to quantitate aspirin along with its metabolite(s) in various biological matrices accurately and precisely to correlate with pharmacological/pharmacodynamic activity. This paper provides a comprehensive overview of various bioanalytical methods (HPLC and LC-MS/MS) that have been reported for direct quantitation of aspirin along with its metabolite(s). The review also provides general information on sample collection, sample processing, internal standard selection, conditions for chromatographic separation, succinct validation data and applicable conclusions for reported assays in a structured manner.

Rapid and sensitive determination of acetylsalicylic acid and salicylic acid in plasma using liquid chromatography-tandem mass spectrometry: application to pharmacokinetic study

A simple and sensitive analytical method using liquid chromatography-tandem mass spectrometry (LC/MS/MS) for determination of acetylsalicylic acid (aspirin, ASA) and its major metabolite, salicylic acid (SA), in animal plasma has been developed and validated. Both ASA and SA in plasma samples containing potassium fluoride were extracted using acetonitrile (protein precipitation) with 0.1% formic acid in it. 6-Methoxysalicylic acid was used as the internal standard (IS). The compounds were separated on a reversed-phase column. The multiple reaction monitoring mode was used with ion transitions of m/z 178.9 --> 136.8, 137.0 --> 93.0 and 167.0 --> 123.0 for ASA, SA and IS, respectively. The lower limits of quantification for ASA and SA were 3 and 30 ng/mL, respectively. The developed method was successfully applied for the evaluation of pharmacokinetics of ASA and SA after p.o. and i.v. administration of 1 mg/kg to rats.

Determination of acetylsalicylic acid and its major metabolite, salicylic acid, in human plasma using liquid chromatography-tandem mass spectrometry: application to pharmacokinetic study of Astrix in Korean healthy volunteers

The first liquid chromatography-tandem mass spectrometry (LC/MS/MS) method for determination of acetylsalicylic acid (aspirin, ASA) and one of its major metabolites, salicylic acid (SA), in human plasma using simvastatin as an internal standard has been developed and validated. For ASA analysis, a plasma sample containing potassium fluoride was extracted using a mixture of ethyl acetate and diethyl ether in the presence of 0.5% formic acid. SA, a major metabolite of ASA, was extracted from plasma using protein precipitation with acetonitrile. The compounds were separated on a reversed-phase column with an isocratic mobile phase consisting of acetonitrile and water containing 0.1% formic acid (8:2, v/v). The ion transitions recorded in multiple reaction monitoring mode were m/z 179 --> 137, 137 --> 93 and 435 --> 319 for ASA, SA and IS, respectively. The coefficient of variation of the assay precision was less than 9.3%, and the accuracy exceeded 86.5%. The lower limits of quantification for ASA and SA were 5 and 50 ng/mL, respectively. The developed assay method was successfully applied for the evaluation of pharmacokinetics of ASA and SA after single oral administration of Astrix (entero-coated pellet, 100 mg of aspirin) to 10 Korean healthy male volunteers.

Stable isotope dilution analysis of salicylic acid and hydroquinone in human skin samples by gas chromatography with mass spectrometric detection

A sensitive and accurate gas chromatographic-mass spectrometric (GC-MS) method has been developed for the quantitative determination of salicylic acid (SA) and hydroquinone (HQ) from human skin samples and cosmetic emulsions. Deuterium labeled SA-d(6) and HQ-d(6) were used as internal standards (IS). The samples were extracted with methanol, dried under nitrogen and derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA)+1% trimethylchlorosilane (TMCS). Quantification was performed in SIM mode with a limit of quantification (LOQ) of 50 ng ml(-1) for SA and 10 ng ml(-1) for HQ. The inter-day variation (R.S.D.) was less than 5% and the accuracy was better than 13.3% for both compounds. The recoveries from the different matrices ranged between 93.1 and 103.3% for SA, and 97.3 and 100.8% for HQ.

Sensitive determination of aspirin and its metabolites in plasma by LC-UV using on-line solid-phase extraction with methylcellulose-immobilized anion-exchange restricted access media

We describe a sensitive determination of aspirin (ASA) and its three metabolites (salicylic acid [SA], 2,3-dihydroxybenzoic acid [2,3-DHBA], and 2,5-dihydroxybenzoic acid [gentisic acid (GA)]) in rat plasma. Analysis was carried out by on-line solid-phase extraction (SPE) using a methylcellulose-immobilized-strong anion-exchanger (MC-SAX), followed by liquid chromatography (LC) coupled with UV detection. The lower limits of quantitation for ASA and SA were 60 ng/mL in 100 microL of plasma, respectively. This method was validated with respect to intra- and inter-day precision, accuracy, and linearity up to concentrations of 20,000 ng/mL for ASA, SA, 2,3-DHBA and gentisic acid, respectively. The method was successfully applied to an analysis of the pharmacokinetics of ASA and SA in rats.

Protein binding of aspirin and salicylate measured by in vivo ultrafiltration

OBJECTIVE

Methods for measuring protein binding of drugs generally require direct measurement of the concentration of unbound drug and thus may require a highly sensitive assay. In vivo ultrafiltration has been used to determine protein binding of endogenous substances. We have examined its value for measuring protein binding of drugs because it requires measurement of only the concentration of total drug, not unbound drug, in plasma.

METHODS

The protein binding of aspirin and its metabolite salicylate was measured in 29 healthy subjects 20 minutes after a single oral dose of 600 mg soluble aspirin, by the new method, in vivo ultrafiltration, as well as by a standard method, in vitro ultracentrifugation.

RESULTS

The data for salicylate were examined systematically to determine the optimal method of determining estimates of protein binding by in vivo ultrafiltration. Estimates of protein binding of salicylate were 81.7% +/- 10.1% (mean +/- SD) by the in vivo method and 81.6% +/- 11.3% by in vitro ultracentrifugation. Bland-Altman analysis of agreement showed that within-individual differences in percentage of protein binding determined by the two methods did not differ significantly from zero (mean difference, 0.07%; 95% confidence interval, -2.33 to +2.46). There was a highly significant correlation between estimates of protein binding by the two methods (r = 0.82; p = 0.001). Protein binding of aspirin was estimated of protein binding by the two methods (r = 0.82; p = 0.001). Protein binding of aspirin was estimated at 58.3% +/- 9.6% by in vivo ultrafiltration and could not be estimated by in vitro ultracentrifugation because the concentration of unbound aspirin in plasma was below the limit of detection for the assay.

CONCLUSION

In vivo ultrafiltration can be used to measure protein binding of drugs and has potential advantages over conventional methods. A sensitive assay may not be required because the unbound drug need not be measured, measurement in vivo may maintain more physiologic conditions, and it may be useful in measuring protein binding of drugs that are degraded rapidly in vitro.

Determination of aromatic metabolites in ruminant urine by high-performance liquid chromatography

A method based on reversed-phase HPLC is reported for the separation and quantification of various urinary aromatic metabolites: hippuric, phenylaceturic, salicyluric, benzoic, phenylacetic, salicylic, 3-phenylpropionic and cinnamic acids and several phenols in ruminant urine. In this method, a Nova-Pak C18 (4 microns) 150 x 3.9 mm I.D. column, two solvents [A: 15% methanol in 20 mM acetic acid (pH 3.3); B: methanol) in a gradient mode at a flow-rate of 0.8 ml/min, and UV detection at 210 nm were used. Quantification of the total (free and conjugated) benzoic, phenylacetic and salicylic acids present in urine was achieved by hydrolysis of the samples in 3 M HCl at 100 degrees C for 24 h prior to HPLC analysis. The lowest detection concentration was 50 mumol/l. This method is useful for scanning the profile of aromatic metabolites in urine of ruminants, which provides information on the diets the animals receive.

Simultaneous determination of acetylsalicylic acid and salicylic acid in human plasma by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method is described for the simultaneous determination of acetylsalicylic acid (ASA) and its main metabolite salicylic acid (SA) in human plasma. Acidified plasma is deproteinized with acetonitrile which is separated from the aqueous layer by adding sodium chloride. ASA and SA are extracted into the acetonitrile layer with high yield, and determined by reversed-phase HPLC (column: Novapak C18 4 microns silica, 150 x 4 mm I.D.; eluent: 740 ml water, 900 microliters 85% orthophosphoric acid, 180 ml acetonitrile) and photometric detection (237 nm). 2-Methylbenzoic acid is used as internal standard. The method allows the determination of ASA and SA in human plasma as low as 100 ng/ml with good precision (better than 10%). The assay was used to determine the pharmacokinetic parameters of ASA and SA following oral administration of 100-500 mg ASA in healthy volunteers.

Salicylate poisoning: two-dimensional J-resolved NMR urinalysis

Identification of a case of acute salicylate intoxication using 300 MHz 1H NMR spectroscopy of a urine sample is reported. It has been achieved by using a combination of a one-dimensional experiment with water presaturation and a two-dimensional homonuclear J-resolved experiment. By these means, lysine and the three major metabolites of acetylsalicylic acid have been assigned in the crude urine. The results are compared with those obtained at 600 MHz and with classical biochemical methods. The use of this method for routine diagnosis in biological analysis is discussed.

Direct gradient reversed-phase high-performance liquid chromatographic determination of salicylic acid, with the corresponding glycine and glucuronide conjugates in human plasma and urine

A gradient reversed-phase HPLC analysis for the direct measurement of salicylic acid (SA) with the corresponding glycine and glucuronide conjugates in plasma and urine of humans was developed. The glucuronides were isolated by preparative HPLC from human urine samples. The concentration of the glucuronides in the isolated fraction were determined after enzymatic hydrolysis. Salicylic acid acyl glucuronide (SAAG) was not present in plasma. No isoglucuronides were present in acidic and alkaline urine of the volunteer. The limits of quantitation in plasma are: SA 0.2 microgram/ml, salicyluric acid (SU) 0.1 microgram/ml, salicylic acid phenolic glucuronide (SAPG) 0.4 microgram/ml and salicyluric acid phenolic glucuronide (SUPG) 0.2 microgram/ml. The limit of quantitation in urine is for all compounds 5 micrograms/ml. Salicylic acid acyl glucuronide is stable in phosphate buffer pH 4.9 during 8 h at 37 degrees C; thereafter it declines to 80% after 24 h. The subject's urine was therefore acidified by the oral intake of 4 x 1.2 g of ammonium chloride/day. With acidic urine, hardly any salicylic acid is excreted unchanged (0.6%). It is predominantly excreted as salicyluric acid (68.7%).

Induction of omega-oxidation of monocarboxylic acids in rats by acetylsalicylic acid

The accumulation of dicarboxylic acids, particularly long chain, is a prominent feature of Reye's syndrome and diseases of peroxisomal metabolism. We assessed the omega-oxidation of a spectrum of fatty acids in rats and asked whether pretreatment of rats with aspirin, which is known to predispose children to Reye's syndrome, would affect omega-oxidation of long chain fatty acids. We found that aspirin increased liver free fatty acids and increased the capacity for omega-oxidation three- to sevenfold. Omega-oxidation of long chain substrate was stimulated to a greater degree than medium chain substrate and was apparent within one day of treatment, at serum aspirin concentrations below the therapeutic range in humans. The apparent Km for lauric acid was 0.9 microM and 12 microM for palmitate. We also found a difference in the storage stability of activity toward medium and long chain substrate. Saturating concentrations of palmitate had no effect on the formation of dodecanedioic acid, whereas laurate decreased but never eliminated the omega-oxidation of palmitate. 97% of the total laurate omega-oxidative activity recovered was found in the microsomes, but 32% of palmitate omega-oxidative activity was present in the cytosol. These results demonstrate that aspirin is a potent stimulator of omega-oxidation and suggest that there may be multiple enzymes for omega-oxidation with overlapping substrate specificity.

A non-extraction HPLC method for the simultaneous determination of serum paracetamol and salicylate

A direct injection HPLC method for the sumultaneous measurement of serum paracetamol and salicylate is described using a Pinkerton internal surface reversed-phase column with benzoic acid as internal standard. The method is linear to at least 1000 mg/L for both drugs and shows good precision at levels of 62-500 mg/L. None of the drugs tested for interference affected the quantitation of either drug. In patient samples, the values obtained with this method correlated well with those from enzymatic paracetamol and Trinder salicylate methods.

Aspirin prolongs bleeding time in uremia by a mechanism distinct from platelet cyclooxygenase inhibition

We reported that aspirin (ASA) abnormally prolongs bleeding time (BT) in uremia. The present study was designed to investigate whether the abnormally prolonged post-ASA BT in uremia is due to different ASA pharmacokinetics and bioavailability that might be a consequence of uremic condition, platelet cyclooxygenase is peculiarly sensitive to ASA in uremia, and ASA affects primary hemostasis in uremia by a mechanism independent of cyclooxygenase inhibition. Our results showed that in patients with uremia, but not in normal subjects, ASA markedly prolongs the BT. This effect is transient and depends on the presence of ASA in the blood. The observed differences in ASA kinetic parameters are not an explanation of the exaggerated effect of ASA on primary hemostasis in uremia. The sensitivity of platelet cyclooxygenase to ASA inhibition is comparable in uremics and in normal subjects. The temporal dissociation between ASA-induced prolongation of BT and the effect on platelet thromboxane A2 generation suggests that ASA inhibits platelet function in uremia by a mechanism distinct from cyclooxygenase blocking. This possibility is strengthened by the observation that ibuprofen at a dose that fully inhibits platelet cyclooxygenase activity does not significantly prolong BT.

Rapid high-performance liquid chromatographic assay for the simultaneous analysis of non-steroidal anti-inflammatory drugs in plasma

A high-performance liquid chromatographic assay has been developed for the determination of a number of non-steroidal anti-inflammatory drugs in plasma. The samples were prepared by adding acetonitrile and perchloric acid to 200 microliter of plasma. Diclofenac, fenoprofen, ketoprofen, naproxen, phenylbutazone, piroxicam and sulindac were quantified in the supernatant produced using a mobile phase of phosphoric acid 0.03% (pH 2.5)-acetonitrile and a detecting wavelength of 254 nm. The reproducibility, linearity, precision and specificity of the assay were determined and found to be satisfactory. Alteration of the detection wavelength to 229 nm also permitted accurate determination of ibuprofen concentration in plasma. While reduction of the organic solvent content of the mobile phase and alteration of wavelength to 313 nm produced a system capable of quantifying salicylate and its metabolites in plasma and by further reducing the detecting wavelength to 237 nm, aspirin also was quantifiable. These methods have been applied in a cross-sectional study of medication compliance among rheumatoid arthritis patients treated with non-steroidal anti-inflammatory drugs.

Disposition of aspirin and its metabolites in the semen of man

The study was undertaken to determine the distribution of aspirin and its metabolites in the semen of humans after an oral dose of aspirin. Each of seven healthy male volunteers was given a single oral dose of 975 mg of aspirin on an empty stomach together with 200 mL of water. Timed samples of blood and semen were obtained from each subject, and the concentrations of aspirin, salicylic acid, and salicyluric acid determined by a specific high-performance liquid chromatographic assay. The mean peak concentration of aspirin was 6.5 micrograms/mL in plasma (range, 4.9-8.9 micrograms/mL), reached in 26 minutes (range, 13-33 minutes). The half-life of aspirin was 31 minutes. The concentration ratio of aspirin (semen/plasma) was 0.12 (except for one subject in whom it was 0.025). The mean peak concentration of salicylate in plasma was 49 micrograms/mL (range, 42-62 micrograms/mL), reached in 2.5 hours (range, 2.0-2.8 hours). Salicylate distributed rapidly into semen and maintained a concentration ratio (semen/plasma) of 0.15. Salicyluric acid (the glycine conjugate of salicylic acid) was found in the semen. Its high concentration in some subjects' semen (four times the concurrent plasma concentration) was attributed to contamination of semen sample with residual urine, containing salicylurate, in the urethra of those who urinated after the dose of aspirin. Possible side effects of aspirin and salicylate in semen include adverse effects on fertility, male-medicated teratogenesis, dominant lethal mutations, and hypersensitivity reactions in the recipients.

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.