Some new aspects of the metabolism of phenacetin in the rat

1. Four new metabolites of phenacetin in the urine of the rat are described; these are (i) N-acetyl-S-ethylcysteine, (ii) quinol, (iii) acetamide and (iv) probably N-acetyl-S-2-(4-ethoxyacetanilido)cysteine S-oxide. 2. Metabolites (i), (iii) and (iv) were characterized and estimated by g.l.c., by t.l.c., by paper chromatography, by chemical reactions or by radioactive techniques after administration to rats of [ethyl-¹⁴C]phenacetin and [acetyl-³H]phenacetin; metabolite (ii), which was excreted mainly as conjugates of sulphuric acid and glucosiduronic acid, was measured by paper chromatography and characteristic colour reactions after enzymic and chemical hydrolysis of the conjugates. 3. Small amounts of azoxy-4-[ethyl-¹⁴C]ethoxybenzene and an unknown metabolite were also found in the urine of rats after administration of [ethyl-¹⁴C]phenacetin. 4. The likely mechanisms and some biological implications of these metabolic reactions are discussed.     

Bound auxin metabolism in cultured crown-gall tissues of tobacco

Bound auxin metabolism in cultured crown-gall tumor cells and pith callus of tobacco was examined by feeding radiolabeled auxins and auxin conjugates. In all tissues fed [¹⁴C]indoleacetic acid (IAA), at least one-third of the IAA was decarboxylated, and most of the remaining radiolabel occurred in a compound(s) which did not release IAA with alkaline hydrolysis. In cells transformed by the A6 strain of Agrobacterium tumefaciens, the only detectable IAA conjugate was indole-3-acetylaspartic acid (IAAsp), whereas cells transformed by the gene 2 mutant strain A66 produced an unidentified amide conjugate but no IAAsp. By contrast, cells fed [¹⁴C]naphthaleneacetic acid (NAA) accumulated several amide and ester conjugates. The major NAA metabolite in A6-transformed cells was naphthaleneacetylaspartic acid (NAAsp), whereas the major metabolites in A66-transformed cells were NAA esters. In addition, A66-transformed cells produced an amide conjugate of NAA which was not found in A6-transformed cells and which showed chromatographic properties similar to the unknown IAA conjugate. Pith callus fed [¹⁴C] NAA differed from both tumor lines in that it preferentially accumulated amide conjugates other than NAAsp. Differences in the accumulation of IAA and NAA conjugates were attributed in part to the high capacity of tobacco cells to oxidize IAA and in part to the specificity of bound auxin hydrolases. All tissues readily metabolized IAAsp and indole-3-acetyl-myo-inositol, but hydrolyzed NAAsp very slowly. Indirect evidence is provided which suggests that ester conjugates of NAA are poorly hydrolyzed as well. Analysis of tissues fed [¹⁴C]NAA together with high concentrations of unlabeled IAA or NAA indicates that tissue-specific differences in NAA metabolism were not the result of variation in endogenous auxin levels. Our results support the view that bound auxin hydrolysis is highly specific and an important factor controlling bound auxin accumulation.     

Formation and biliary excretion of glutathione conjugates of bile acids in the rat as shown by liquid chromatography/electrospray ionization-linear ion trap mass spectrometry

Acyl-adenylates and acyl-CoA thioesters of bile acids (BAs) are reactive acyl-linked metabolites that have been shown to undergo transacylation-type reactions with the thiol group of glutathione (GSH), leading to the formation of thioester-linked GSH conjugates. In the current study, we examined the transformation of cholyl-adenylate (CA-AMP) and cholyl-coenzyme A thioester (CA-CoA) into a cholyl-S-acyl GSH (CA-GSH) conjugate by rat hepatic glutathione S-transferase (GST). The reaction product was analyzed by liquid chromatography (LC)/electrospray ionization (ESI)-linear ion trap mass spectrometry (MS). The GST-catalyzed formation of CA-GSH occurred with both CA-AMP and CA-CoA. Ursodeoxycholic acid, lithocholic acid, and 2,2,4,4-²H₄-labeled lithocholic acid were administered orally to biliary fistula rats, and their corresponding GSH conjugates were identified in bile by LC/ESI-MS². These in vitro and in vivo studies confirm a new mode of BA conjugation in which BAs are transformed into their GSH conjugates via their acyl-linked intermediary metabolites by the catalytic action of GST in the liver, and the GSH conjugates are then excreted into the bile.     

Studies on the metabolites of phylloquinone (vitamin K1) in the urine of man

The nature of the metabolites excreted in the urine was investigated up to 48 h after oral and intravenous administration of 0.3 to 1.3 mg [1′,2′-³H₂]phylloquinone. The metabolites were water-soluble of which the major fraction consisted of glucuronide conjugates. A chromatographic comparison of the aglycone fragments released by β-glucuronidase and by dilute HCl revealed the presence of at least three labelled aglycones. The major aglycones obtained by enzyme hydrolysis consisted of at least two closely related organic acids which were not separated by adsorption thin-layer chromatography but one of which on treatment with dilute acid yielded a neutral metabolite with the chromatographic properties of phylloquinone γ-lactone. The results suggest that phylloquinone γ-lactone, the only previously isolated urinary metabolite of phylloquinone, is an artifact produced by the conditions of acid hydrolysis. Although the acid labile aglycone was the minor component of the two acid metabolites, its proportion in urine extracts as measured by conversion to the lactone, increased with the time after administration of labelled phylloquinone.     

Reversed-phase chromatography of urinary metabolites of paracetamol using ion suppression and ion pairing

High-performance liquid chromatography (HPLC) has proven particularly useful for the study of paracetamol metabolism. Two alternative methods were developed using reversed-phase C₁₈ columns. A rapid ion suppression technique was used for the analysis of free paracetamol, paracetamol mercapturic acid and cysteine conjugate in urine samples obtained from isolated perfused rat kidney preparations, which has conveniently demonstrated the oxidative metabolic capacity of the kidney towards paracetamol. A somewhat longer, but higher resolution, ion-pair HPLC procedure was developed for the analysis of paracetamol metabolites in urine samples from experimental animals. The ion-pairing solvent was composed of tetrabutylammonium hydroxide, Tris and EDTA buffered to pH 7.2 with phosphoric acid. Gradient programming was further used to enhance resolution. Using this system two new metabolites, the sulphate and glucuronide conjugates of 3-thiomethyl-paracetamol were detected and routinely determined along with other known paracetamol metabolites, viz. free paracetamol, paracetamol sulphate, glucuronide, mercapturic acid, and cysteine conjugates, 3-methoxyparacetamol glucuronide and sulphate, p-aminophenol and its O-glucuronide and O-sulphate conjugates. Phenolic O-substituted glucuronide and sulphate conjugates of N-hydroxyparacetamol were also separated.     

Method for combined analysis of profiles of conjugated progesterone metabolites and bile acids in serum and urine of pregnant women

A method for analysis of profiles of conjugated progesterone metabolites and bile acids in 10 ml of urine and 1–4 ml of serum from pregnant women is described. Total bile acids and neutral steroids from serum and urine were extracted with octadecylsilane-bonded silica. Groups of conjugates were separated on the lipophilic ion-exchanger triethylaminohydroxypropyl Sephadex LH-20 (TEAP-LH-20). Fractions were divided for steroid or bile acid analyses. Sequences of hydrolysis/ solvolysis and separations on TEAP-LH-20 permitted separate analyses of steroid glucuronides, monosulfates and disulfates and bile acid aminoacyl amidates, sulfates, glucuronides and sulfate-glucuronides. Radiolabelled compounds were added at different steps to monitor recoveries and completeness of separation, and hydrolysis/solvolysis of conjugates was monitored by fast-atom bombardment mass spectrometry. The extraction and solvolysis of steroid disulfates in urine were studied in detail, and extraction recoveries were found to be pH-dependent. Following methylation of bile acids, all compounds were analysed by capillary gas chromatography and gas chromatography—mass spectrometry of their trimethylsilyl ether derivatives. Semiquantification of individual compounds in each profile by gas—liquid chromatography had a coefficient of variation of less than 30%. The total analysis required 3 days for serum and 4 days for urine.     

Simultaneous determination of trimethoprim,sulphamethoxazole and N4-acetylsulphamethoxazole in serum and urine by high-performance liquid chromatography

The simultaneous determination of trimethoprim, sulphamethoxazole and N⁴-acetyl-sulphamethoxazole in serum and urine by high-performance liquid chromatography using sulphafurazole as internal standard is described. The separation was achieved on a reversed-phase column employing acetic acid—methanol as the mobile phase with spectrophotometric detection at 230 nm. Precise simultaneous quantitative analysis of the relative components has been achieved at levels of 0.1 μg/ml for trimethoprim and 1.0 μg/ml for both sulphamethoxazole and its N⁴-acetyl metabolize using 1 ml of serum or urine.     

Isolation and identification of major ecdysteroid conjugates from the ovaries of Bombyx mori

Six major ecdysteroid conjugates have been isolated from mature ovaries of Bombyx mori by a procedure involving column chromatography on Sephadex G15, silicic acid and Sephadex LH-20, and high-performance liquid chromatography using a reverse-phase column. By analyses including ultraviolet absorption, enzymatic hydrolysis, negative ion fast-atom bombardment mass spectrometry and proton and ³¹P nuclear magnetic resonance spectrometry, these conjugates were identified as the following: ecdysone-22-phosphate, 20-hydroxyecdysone-22-phosphate, 2-deoxyecdysone-22-phosphate, 2-deoxy-20-hydroxyecdysone-22-phosphate, 2,22-dideoxy-20-hydroxyecdysone-3-phosphate and bombycosterol-3-phosphate.     

Characterization of a novel diclofenac metabolite in human urine by capillary gas chromatography-negative chemical ionization mass spectrometry

A sensitive analytical method was developed to characterize diclofenac metabolites in small amounts of body fluids. Desalted and lyophilized urine samples were extracted with supercritical carbon dioxide directly or after acidic hydrolysis. The extracts were derivatized with N-tert.-butyldimethylsilyl-N-methyltrifluoroacetamide. The derivatives were separated by capillary gas chromatography and identified by negative chemical ionization mass spectrometry. Full mass spectra were obtained at a level of 1·10⁻⁹ g/ml. With direct extraction, the metabolites could be analysed in one step as open-chained acids and as (cyclic) oxindoles. By acidic hydrolysis the conjugates were transformed to the oxindoles. With both methods, a new main metabolite, [2-[(2,6-dichloro-4-hydroxy-3-methoxyphenyl)amino]phenyl]acetic acid, was identified. The mechanism of its formation is discussed.     

Metabolism of Indole-3-Acetic Acid by Pericarp Discs from Immature and Mature Tomato (Lycopersicon esculentum Mill)

[1′-¹⁴C, ¹³C₆]Indole-3-acetic acid was infiltrated into immature pericarp discs from fruits of tomato (Lycopersicon esculentum Mill., cv Moneymaker). After a 24-h incubation period the discs were extracted with methanol and the partially purified extract was analyzed by reversed-phase high-performance liquid chromatography-radiocounting. Five metabolite peaks (1-5) were detected and subsequently analyzed by combined high-performance liquid chromatography-frit-fast atom bombardment-mass spectrometry. The metabolite 4 fraction was found to contain [¹³C₆]-indole-3-acetylaspartic acid, and analysis of metabolite 5 identified [¹³C₆]indole-3-acetyl-β-d-glucose. The other metabolites could not be identified, but alkaline hydrolysis studies and gel permeation chromatography indicated that metabolites 1 and 3 were both amide conjugates with a molecular weight of approximately 600. Studies with radiolabeled indole-3-acetic acid, indole-3-acetylaspartic acid, and indole-3-acetyl-β-d-glucose demonstrated that in immature pericarp indole-3-acetic acid is deactivated primarily via metabolism to indole-3-acetylaspartic acid, which is further converted to metabolites 1, 2, and 3. In mature, pink pericarp discs, indole-3-acetic acid is converted more extensively to its glucosyl conjugate. Conjugation of indole-3-acetic acid to indole-3-acetylaspartic acid appears to be dependent upon protein synthesis because it is inhibited by cycloheximide. In contrast, cycloheximide has little effect on the further conversion of indole-3-acetylaspartic acid to metabolites 1, 2, and 3.     

Detoxications in peripatus. Sulphate, phosphate and histidine conjugations

Phenols were detoxified in the Onycophoran Peripatoides novaezealandiae by conjugation with sulphuric acid and phosphoric acid, but no evidence for a glycoside detoxication could be found. [(14)C]Benzoic acid was metabolized in 24h to N(2)-benzoyl-l-histidine, which was identified by electrophoresis, chromatography and dilution analysis. Similar conjugates were formed with p-aminobenzoic acid and p-nitrobenzoic acid. In longer-duration experiments further unidentified metabolites were formed, two of which appeared to result from the further metabolism of the histidine conjugate.     

Role of IAA conjugates in inducing ethylene production by tobacco leaf discs

Indole-3-acetic acid (IAA) labeled in its carboxyl group was metabolized by tobacco leaf discs (Nicotiana tabacum L. cv. Xanthi) into three metabolites, two of which were preliminarily characterized as a peptide and an ester-conjugated IAA. Reapplication of each of the three metabolites (at 10 μM) resulted in a marked stimulation of ethylene production and decarboxylation by the leaf discs. Similarly, these three IAA metab olites could induce elongation of wheat coleoptile segments, which was accompanied by decarboxylation. Both the exogenously supplied esteric and peptidic IAA conjugates were converted by the leaf discs into the same metabolites as free IAA. (1-¹⁴C)IAA, applied to an isolated epidermis tissue, was completely metabolized to the esteric and peptidic IAA conjugates. This epidermis tissue showed much higher ethylene production rates and lower decarboxylation rates than did the whole leaf disc. The results suggest that the participation of IAA conjugates in the regulation of various physiological processes depends on the release of free IAA, which is obtained by enzymatic hydrolysis of the conjugates in the tissue. The present study demonstrates biological activity of endogenous IAA conjugates that were synthesized by tobacco leaf discs in response to exogenously supplied IAA.     

Ecdysone metabolism and distribution during the pupal-adult development of Manduca sexta

The metabolism and distribution of endogenous ecdysone and injected [³H]ecdysone were studied during the pupal-adult development of Manduca sexta. Well-characterized antisera were used to detect and quantify endogenous metabolites by radioimmunoassay (RIA) following their separation by ion-suppressed reverse phase, and normal phase, high performance liquid chromatography. Identical chromatographic procedures were employed to determine the metabolic fate of the [³H]ecdysone in the haemolymph pool. These studies revealed the sequential appearance in the haemolymph and gut of progressively oxidized metabolites of ecdysone—hydroxylation at C-20 was followed by hydroxylation at C-26. The data are suggestive of both the induction of the steroid hydroxylases (oxidases) by substrate or other effector substances and the possible coordination of developmental events by ecdysteroids other than 20-hydroxyecdysone.In the haemolymph, two highly-polar conjugates of ecdysone were observed together with conjugates of the other free ecdysteroids, especially those hydroxylated at C-26. In contrast, relatively little 20-hydroxycdysone conjugate was detected in the insect. As adult development proceeded, both endogenous and radiolabelled ecdysteroids were increasingly localized in the gut, so that just prior to eclosion most ecdysteroids were present in the meconium of the high gut (rectal pouch). The peak titres and the kinetics of appearance of ecdysone, 20-hydroxyecdysone, and 20,26-dihydroxyecdysone were similar for both haemolymph and gut (and for males and females), but considerably higher levels of C-26 oxidized (acid) metabolites of ecdysone and 20-hydroxyecdysone were localized in the gut. Although levels of highly-polar ecdysteroid conjugates found in the haemolymph and gut were similar, considerable amounts of three less polar ecdysone conjugates, of 3-α-epimers of ecdysone and 20-hydroxyecdysone, and of a substance tentatively identified as 2-deoxyecdysone were found only in the gut. Whether ionized, conjugated, or free, the gut ecdysteroids did not appear to equilibrate with the haemolymph compartment.Differences were observed in the metabolism kinetics of exogenously administered radiolabelled ecdysone when compared to the endogenous ecdysteroids; and some RIA positive gut metabolites did not become significantly radiolabelled. This suggests that injection of ecdysone may not simulate the endogenous secretion of ecdysone or its subsequent metabolism and distribution completely accurately.     

Excretion of estrone,estradiol, and progesterone in the urine and feces of the female cotton-top tamarin (Saguinus oedipus oedipus)

The excretion of three gonadal steroids was studied in the urine and feces of female cotton-top tamarins (Saguinus oedipus oedipus). Each steroid, ¹⁴C-estrone, ¹⁴C-estradiol, and ¹⁴C-progesterone, was injected into a separate female cotton-top tamarin. Urine and feces were collected at 8 hr intervals for 5 days on the three tamarins. Samples were analyzed to determine the proportion of free and conjugated steroids. Steroid excretion patterns were determined by sequential ether extraction, enzyme hydrolysis, and chromatography. Labeled estrone was excreted in a slow and continuous manner into the urine (57%) and feces (43%) with 90% of the steroid conjugated. The nonconjugated form had an elution profile identical to ³H estrone, but the conjugated portion was not completely hydrolyzed by enzyme. Labeled estradiol was excreted primarily in the urine (87%) and was released rapidly. Over 90% of the injected ¹⁴C-estradiol was excreted in urine as a conjugate, of which 41% was converted to an estrone conjugate and the remaining 59% was excreted as a polar estradiol conjugate. Labeled progesterone was excreted primarily in the feces (95%), 61% of which was free steroid. Four to six individual peaks of radioactivity were found when using celite chromatography and high performance liquid chromatography (HPLC), indicating that progesterone is metabolized into several urinary and fecal metabolites. One of these peaks matched ³H-progesterone and others may be pregnanediols, pregnanetriols, and 17-hydroxyprogesterone. These steroidal excretion patterns help explain the atypical hormonal patterns seen during the tamarin ovarian cycle.     

Metabolism of Indole-3-Acetic Acid: III. Identification of Metabolites Isolated from Crown Gall Callus Tissue

The metabolism of labeled indole-3-acetic acid (IAA-2-¹⁴C) was investigated in Parthenocissus tricuspidata crown gall callus tissue. After 48 hours incubation, 85 to 90% of the supplied IAA was taken up by the tissue, and of that taken up, about 45% was conjugated with five amino acids. The conjugates found were aspartic and glutamic acid (minor ones) as well as glycine, alanine, and valine (major ones). The last four are being reported for the first time as metabolites of IAA. These conjugates were identified through their chromatographic properties, hydrolysis products, and their mass spectra. The possible significance of these amino acid conjugates is discussed.     

In vitro ecdysteroid conjugation by enzymes of Manduca sexta midgut cytosol

In incubations with 80,000g supernatant of Manduca sexta midgut homogenates, [³H]ecdysone was converted to 3-[³H]epiecdysone and tritiumlabeled highly polar metabolites. C₁₈ SEP-PAK cartridges were found suitable for the separation and purification of the free ecdysteroids and of the highly polar metabolites. Eighty to ninety percent of the metabolites were hydrolyzed by enzyme mixtures (mainly β-glucuronidase, sulphatase, and acid phosphatase) from molluscs, even when β-glucuronidase activity was completely inhibited by D-saccharic acid 1,4-lactone, or various human acid phosphatases (free of sulphatase activity). In each experiment, the hydrolysate contained a much higher proportion of 3-epiecydsone than the free (unconjugated) ecdysteroid fraction. [³H]ecdysone was not metabolized in anaerobic incubations of midgut supernatant that had been filtered through Sephadex G-25. Addition of 5 mM ATP and 5 mM Mg²⁺ restored the conjugate formation in incubations of Sephadex-filtered supernatant. Four ecdysone conjugates and two 3-epiecdysone conjugates were resolved by reversedphase ion-pair high-performance liquid chromatography. It is concluded that the midgut cytosol contains several ATP:ecdysteriod phosphotransferases. This is the first demonstration of the formation of ecdysteroid phosphoconjugates in a cell-free system.     

Analysis of metabolic profiles of prostaglandins in urine using a lipophilic anion exchanger

A method is described for the fractionation of prostaglandins and their metabolites in urine. Following acidification and extraction on Amberlite XAD-2, samples were separated by chromatography on the lipophilic anion exchanger diethyl-aminohydroxypropyl Sephadex LH-20 into fractions containing neutral compounds, monocarboxylic, dicarboxylic and polycarboxylic acids. The compounds in resulting fractions were further separated by reversed phase partition chromatography. As an application, the metabolic profiles in urine of [9β-^3H]-labeled prostaglandin F_2α¹ and prostaglandin analogs 15-methyl-PGF_2α and 16,16-dimethyl-PGF_2α were investigated in the cynomolgus monkey. It was demonstrated that the resolution of individual prostaglandin metabolites by reversed phase partition chromatography was considerably simplified by initial group separation on the anion exchanger, and several metabolites were much purified. A glucuronic acid conjugate of the main metabolite of 15-methyl-PGF_2α (dinor-15-methyl-PGF_2α) was tentatively identified using computerized gas chromatography - mass spectrometry.     

Excretion of norsteroids’ phase II metabolites of different origin in human

The urinary phase II metabolites of norsteroids, 19-norandrosterone, 19-noretiocholanolone and 19-norepiandrosterone glucuronide and sulphate, were analyzed in samples collected during the pregnancy, following the administration of norsteroids or the consumption of edible parts of non-castrated pig and in athletes’ samples in which they were found during routine controls. The level of the sulfo- and glucuroconjugated metabolites was precisely determined by GC/HRMS, after selective hydrolysis. The goal was to evaluate whether the fine analysis of the norsteroid conjugates produced and excreted in different conditions would show a pattern that could be linked to their origin. The delta ¹³C values of the metabolites formed following the ingestion of edible parts of non-castrated pig were measured by isotope ratio mass spectrometry. Our results indicated that it is not possible to determine the origin of the urinary metabolites based upon the sole evaluation of the different metabolites and conjugates. The GC/C/IRMS is the only method permitting to distinguish between the exogenous and endogenous origin of the metabolites.     

Intrahepatic conversion of a glutathione conjugate to its mercapturic acid. Metabolism of 1-chloro-2,4-dinitrobenzene in isolated perfused rat and guinea pig livers

Because of the low hepatic activity of gamma-glutamyl-transferase in the rat, the liver is generally considered to play only a minor role in the degradation of glutathione conjugates, a limiting step in mercapturic acid formation. Recent findings indicate, however, that the liver has a prominent role in glutathione catabolism, particularly in species other than rat. To examine the contributions of liver to mercapturic acid biosynthesis, mercapturate formation was compared in isolated perfused livers from rats and guinea pigs dosed with either 0.3 or 3.0 mumol of 1-chloro-2,4-dinitrobenzene (CDNB). Chemically synthesized glutathione conjugate, mercapturic acid, and intermediary metabolites of CDNB were used as standards in the high performance liquid chromatography analysis of bile and perfusate samples. Biliary excretion accounted for almost all of the recovered metabolites. A marked species difference was observed in the pattern of CDNB metabolism. Rat livers dosed with 0.3 mumol of CDNB excreted 55% of total biliary metabolites as the glutathione conjugate and 8.2% as the mercapturic acid, whereas guinea pig livers excreted only 4.8% as the glutathione conjugate and 47% as the mercapturate. Mercapturic formation was also dose-dependent, with a larger fraction formed at the 0.3- versus the 3.0-mumol dose (8.2 versus 3.7% in the rat; 47 versus 19% in the guinea pig). Hepatic conversion of the glutathione conjugate to the mercapturic acid was markedly inhibited in both species after retrograde intrabiliary infusion of acivicin, an inhibitor of gamma-glutamyltransferase activity. These findings provide direct evidence for intrahepatic biosynthesis of mercapturic acids. Thus, glutathione conjugates synthesized within hepatocytes are secreted into bile and broken down to cysteine conjugates; the latter are then presumably reabsorbed by the liver, N-acetylated to form the mercapturic acid and re-excreted into bile.     

A radioimmuno—chromatographic scanning method for the analysis of testosterone conjugates in urine and serum

A method for the analysis of testosterone (and 5α-dihydrotestosterone) conjugates in human serum and urine samples is described. The samples were brought to pH 1 and extracted with a diethyl ether—methanol mixture. After evaporation the residues were run in a thin-layer chromatography system, individual samples' paths were cut into 1-cm long pieces and eluted with methanol. The methanol was evaporated and the residue subjected to acid hydrolysis. The released steroid was extracted by diethyl ether and measured by radioimmunoassay. The methodology described represents a new approach to the qualitative and quantitative study of steroid conjugates in serum and urine, and can easily be applied to the study of steroid conjugates in other biological material.