Novel direct high-performance liquid chromatographic method for determination of salicylate glucuronide conjugates in human urine

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.

Direct analysis of salicylic acid, salicyl acyl glucuronide, salicyluric acid and gentisic acid in human plasma and urine by high-performance liquid chromatography

A method for the simultaneous direct determination of salicylate (SA), its labile, reactive metabolite, salicyl acyl glucuronide (SAG), and two other major metabolites, salicyluric acid and gentisic acid in plasma and urine is described. Isocratic reversed-phase high performance liquid chromatography (HPLC) employed a 15-cm C18 column using methanol-acetonitrile-25 mM acetic acid as the mobile phase, resulting in HPLC analysis time of less than 20 min. Ultraviolet detection at 310 nm permitted analysis of SAG in plasma, but did not provide sensitivity for measurement of salicyl phenol glucuronide. Plasma or urine samples are stabilized immediately upon collection by adjustment of pH to 3-4 to prevent degradation of the labile acyl glucuronide metabolite. Plasma is then deproteinated with acetonitrile, dried and reconstituted for injection, whereas urine samples are simply diluted prior to injection on HPLC. m-Hydroxybenzoic acid served as the internal standard. Recoveries from plasma were greater than 85% for all four compounds over a range of 0.2-20 micrograms/ml and linearity was observed from 0.1-200 micrograms/ml and 5-2000 micrograms/ml for SA in plasma and urine, respectively. The method was validated to 0.2 microgram/ml, thus allowing accurate measurement of SA, and three major metabolites in plasma and urine of subjects and small animals administered salicylates. The method is unique by allowing quantitation of reactive SAG in plasma at levels well below 1% that of the parent compound, SA, as is observed in patients administered salicylates.

beta-Naphthoflavone- and self-induced metabolism of 3,3',4,4'-tetrachlorobiphenyl in hepatic microsomes of the male, pregnant female and foetal rat

1. The in vitro metabolism of 3,3',4,4'-tetrachloro-[14C]-biphenyl ([14C]-TCB) by hepatic microsomes from the Wistar rat was investigated with liver microsomes from the male, pregnant female and foetus. 2. Three hydroxylated metabolites (4-OH-3,3',4,5'-tetrachlorobiphenyl, 5-OH-3,3',4,4'-tetrachlorobiphenyl, and 6-OH-3,3',4,4'-tetrachlorobiphenyl) were identified by hplc and gc-ms after incubations of liver microsomes from the beta-naphthoflavone-pretreated male rat and TCB-treated pregnant rat. No metabolites of [14C]-TCB were found after incubation with foetal liver microsomes from dams pretreated with [14C]-TCB. The results indicate that the in vivo accumulation of 4-OH-tetraCB in the foetal compartment is probably due to transplacental transport rather than the formation of this metabolite in the foetus. 3. Pretreatment of the male rat with beta-naphthoflavone substantially induced the formation of hydroxylated metabolites, but pretreatment with phenobarbital and dexamethasone was without effect. Based on in vitro incubations of liver microsomes from the beta-naphthoflavone pretreated male rat, an apparent Km and Vmax of 4.5 microM and 240 pmol/mg protein/min respectively was determined for the metabolism of [14C]-TCB. The formation of phenolic metabolites of [14C]-TCB was most likely dependent on P4501A induction.

Distribution of salicylate in pigmented rabbit ocular tissues after application of a prodrug, sodium monomethyl trisilanol orthohydroxybenzoate: in vivo and ex vivo studies

SMB (sodium monomethyl trisilanol orthohydroxybenzoate) is an organic complex of silicium and salicylate and the main component of a collyrium used in lens transparency abnormalities. Biotransformation and penetration of salicylate in the whole eyeball have been investigated in vivo after repeated instillations of those 14C-radiolabeled eyedrops. We also studied more accurately the salicylate diffusion within the lens under ex vivo conditions. In vivo experiments demonstrated that 8 to 48 hours after the last instillation, radioactivity was detectable in most tissues and remained stable except in the chorioretina. The following gradient of distribution was observed: conjunctiva > cornea > iris-ciliary body > chorioretina > lens > vitreous body > aqueous humor >> plasma and blood. The diffusion of the radiolabeled compound in lens fibres was low, but a more important retention was observed in lens capsule. Though salicylate-metabolizing activities have been demonstrated in ocular tissues, no biotransformation could be detected under our experimental conditions. The lens SA-biotransformation activity was reported to be low and we can most probably consider that, in our ex vivo pharmacokinetic study, the lens metabolite amounts were negligible compared with the salicylate levels. Under such conditions, results showed that the salicylate reached a steady-state between 6 and 12 hours of incubation, characteristic of a passive diffusion mechanism. Quantitative image analysis of lens section autoradiograms revealed a more intense labeling of the anterior part of the lens and suggests that the lens epithelium may facilitate the salicylate diffusion. Furthermore, renal excretion is important since 40% of the administered eyedrops were eliminated during the study period.

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%).

Model representation of salicylate pharmacokinetics using unbound plasma salicylate concentrations and metabolite urinary excretion rates following a single oral dose

The pharmacokinetics of salicylic acid (SA) and its metabolites have been studied in 5 volunteers after administration of 3 g salicylic acid (as sodium salicylate) and collection of serial samples of blood and urine. SA and its metabolites were assayed with a HPLC method specific for each species. The urinary excretion rates of individual metabolites were analyzed using unbound plasma SA concentrations and Lineweaver-Burke plots. The analysis confirmed that the formation of SA urate (SU) and SA phenolic glucuronide (SPG) metabolites are saturable processes, and showed that the Michaelis-Menten values derived are consistent with earlier estimates derived solely from urinary data. The unbound salicylate plasma concentration-time profiles were then analyzed with various models assuming either saturable clearances for metabolite formation and/or saturable protein binding. The data were best described with a model that included both saturable protein binding and saturable metabolism. The model assumed first-order absorption kinetics and instantaneous distribution into extravascular and tissue compartments. The model was validated by comparing predicted relationships between the apparent volume of distribution, clearance, and plasma salicylate concentrations with previous relationships obtained using steady state data.