Studies on the metabolism and excretion of benzyl isothiocyanate in man.

1. Both after ingestion of benzyl isothiocyanate (BITC), a compound with antibacterial properties, and after consumption of garden cress known to contain BITC, the metabolite N-acetyl-S-(N-benzylthiocarbamoyl)-L-cysteine was identified in the urine of volunteers by comparative chromatography. 2. The chemical structure of the metabolite was confirmed by elemental analysis and by comparison of the i.r. and 1H-n.m.r. spectra with those of the synthetic product. 3. On average 53.7% of the dose of BITC was excreted as this metabolite by the renal route. 4. The metabolite was excreted rapidly, appearing with maximum concentrations some 2-6 h after dosing and being essentially complete 10-12 h after administration.

Studies on the metabolism of aristolochic acids I and II.

1. After oral administration of aristolochic acid I (AAI) and aristolochic acid II (AAII) to rats, the following metabolites were isolated from the urine and their structures elucidated: aristolactam I, aristolactam Ia, aristolochic acid Ia, aristolic acid I and 3,4-methylenedioxy-8-hydroxy-1-phenanthrenecarboxylic acid (metabolites of AAI); or aristolactam Ia, aristolactam II and 3,4-methylenedioxy-1-phenanthrenecarboxylic acid (metabolites of AAII). A further metabolite of AAII having a lactam structure has not yet been isolated in pure form. 2. The metabolic pathways have been elucidated by administration of various metabolites. 3. The principal metabolite of AAI in rats was aristolactam Ia; 46% of the dose was excreted in the urine in form of this metabolite and 37% in the faeces. The other substances were minor metabolites. Those metabolites of AAII whose structures have been elucidated were minor metabolites; the largest proportion consisted of aristolactam II, which accounted for 4.6% in the urine and 8.9% in the faeces. 4. The mouse was the only animal which had the same metabolite patterns of AAI and AAII as those found in the rat. Not all the metabolites listed above were found in urine from guinea pigs, rabbits, dogs and man.

Determination of N-acetyl-S-(N-alkylthiocarbamoyl)-L-cysteine, a principal metabolite of alkyl isothiocyanates, in rat urine.

A simple and rapid analytical procedure is described for N-acetyl-S-(N-alkylthiocarbamoyl)-L-cysteine (alkyl = benzyl, allyl, methyl, ethyl or n-butyl), a mercapturic acid with an unstable dithiocarbamic acid ester structure, which is found in rat urine as the principal metabolite of the corresponding alkyl isothiocyanate. Because such mercapturic acids decompose at pH values greater than 5 to N-acetylcysteine and alkyl isothiocyanate, the free isothiocyanate is converted with n-butylamine into the corresponding disubstituted thiourea, and, after extraction, measured by high-performance liquid chromatography using an ultraviolet detector. The recovery is ca. 100% and the precision is very good. The lower limit of detection is ca. 0.5 microgram of thiourea. The 24-h renal excretion of these mercapturic acids was determined in rats after administration of benzyl, allyl, methyl, ethyl or n-butyl isothiocyanate.

Pharmacokinetic studies of alizarin in man.

Alizarin, a constituent of the madder root, is employed in phytotherapy to prevent recurrences of calcium-containing urinary stones. Pharmacokinetic studies were carried out in human subjects during the development of a pharmaceutical product containing alizarin. After giving a single oral dose of 210 mg of alizarin there were two maxima in the serum concentration curves, the first at 2-4 h and the second at 6-8 h. Alizarin and its glucuronide conjugate were detected in both maxima by TLC. The mean elimination half-life was 12 h. The amounts excreted in the urine within 6 days ranged from 18.1 to 36.3%, and the amounts in the faeces from 21.6 to 33.0% (total recovery: 40-60%). In bile from a patient who had undergone cholecystectomy only 0.6% of the dose was recovered. To exclude any possibility that alizarin might be bound to calcium ions in bone, bone trephine specimens were examined from patients with oxalate stones who had previously been treated with alizarin for several years. No alizarin was detectable in these samples. When alizarin is mixed with fresh human faeces and incubated anaerobically it undergoes rapid bacterial decomposition. This in vitro experiment indicates that when alizarin is given orally a large proportion is broken down by bacterial action in the intestine.

Pharmacokinetic studies with silymarin in human serum and bile.

Six subjects were given orally 560 mg of silymarin (silibinin 240 mg = 8 Legalon 70 dragees). The serum concentration curves and urinary excretion of silibinin, the principal constituent of silymarin, were measured. The maximum serum concentrations were low, ranging from 0.18 to 0.62 microgram/ml. The same was true of renal excretion, which amounted to only 1-2% of the silibinin dose over 24 hours. However, after giving 140 mg of silymarin (silibinin: 60 mg) to patients who had undergone cholecystectomy, bile collected from the T-tube drains was found to contain maximum silibinin concentrations of between 11 and 47 micrograms/ml. Though the dose was four times lower than in the previous experiments, these concentrations were approximately 100 times higher than in the serum. Because complete collection of bile from these patients was impossible and because it was not possible to collect individual samples in the time interval from 12-24 h, the conventional pharmacokinetic parameters required for bioavailability studies could not be calculated. However, computation of the value for AUC0-24 and for "mean time" (MT) provided data which enabled bioavailability comparisons to be made. A study in which the absorption of Legalon 35 and Legalon 70 dragees was compared provides an example for such bioavailability investigations in the bile.

Metabolism of some naturally occurring isothiocyanates in the rat.

The metabolism of methyl, ethyl, butyl and allyl isothiocyanate, which occur as glucosinolates in a number of plants, was studied. Oral administration of the substances to the rat was followed by their renal excretion as mercapturic acids, which were isolated as dicyclohexylamine salts. Chemical structure was determined by synthesis and 1H-n.m.r. spectra. The mercapturic acids were very labile dithiocarbamidic acid esters, formed by the addition of the isothiocyanate group to the SH group of the cysteine component.

The metabolism of benzyl isothiocyanate and its cysteine conjugate in guinea-pigs and rabbits.

1. Following oral administration of benzyl isothiocyanate or its cysteine conjugate the major metabolite isolated from urine of guinea-pigs and rabbits was a cyclic mercaptopyruvate conjugate, 4-hydroxy-4-carboxy-3-benzylthiazolidin-2-thione. 2. Renal excretion of the metabolite after oral administration of benzyl isothiocyanate or its cysteine conjugate to guinea-pigs amounted to 23% and 33% respectively. The corresponding N-acetylcysteine conjugate of benzyl isothiocyanate (a mercapturic acid) was present as a minor metabolite. 3. After oral or i.v. administration of the glutathione, cysteinylglycine, cysteine or N-acetylcysteine conjugates of benzyl isothiocyanate to guinea-pigs, the major metabolite in urine was 4-hydroxy-4-carboxy-3-benzylthiazolidin-2-thione, with the N-acetylcysteine conjugate of benzyl isothiocyanate present in traces only. 4. It is concluded that during formation of the cyclic mercaptopyruvate conjugate, the cysteine conjugate predominantly undergoes transamination, and only a small proportion undergoes N-acetylation.

[Elimination of drugs in cholecystectomized patients. Studies with silymarin in patients with extrahepatic complications]. / Elimination von Pharmaka bei cholezystektomierten Patienten. Untersuchungen mit Silymarin bei Patienten mit ausserhepatischen Begleiterkrankungen.

Following a single oral administration of silymarin (Legalon) approx. 7-15% of its main component silybin was determined in the 24 h-bile of 10 cholecystectomized patients with T-drainage. In one case the value was 25%. Considering that through the T-tube only one to two thirds of the bile output can be collected and consequently analysed, the total amount of silybin eliminated via the bile must be estimated higher. There didn't appear to be a relationship between the amounts of bile and silybin. In further 4 female patients the silybin excretion measured for 24 h was decreased (values of 1-4%) and the elimination was considerably delayed. Two of these 4 females with reduced elimination of silybin suffered from diabetes mellitus, one from pancreatitis and the fourth from a carcinoma of the stomach metastasising into the liver. Only in the patient with liver metastasis and in that with pancreatitis was the reduced silybin elimination linked with a decrease in bile output. The remaining two females neither showed a correlation between bile output nor amount of silybin excreted. In the one diabetic female the bile collected for 24 h was considerably high, i.e. more than 1 litre. As reasons for the decrease in the biliary elimination of silybin an impairment of metabolism and absorption are discussed.

The metabolism of benzyl isothiocyanate and its cysteine conjugate.

1. The corresponding cysteine conjugate was formed when the GSH (reduced glutathione) or cysteinylglycine conjugates of benzyl isothiocyanate were incubated with rat liver or kidney homogenates. When the cysteine conjugate of benzyl isothiocyanate was similarly incubated in the presence of acetyl-CoA, the corresponding N-acetylcysteine conjugate (mercapturic acid) was formed. 2. The non-enzymic reaction of GSH with benzyl isothiocyanate was rapid and was catalysed by rat liver cytosol. 3. The mercapturic acid was excreted in the urine of rats dosed with benzyl isothiocyanate or its GSH, cysteinyl-glycine or cysteine conjugate, and was isolated as the dicyclohexylamine salt. 4. An oral dose of the cysteine conjugate of [14C]benzyl isothiocyanate was rapidly absorbed and excreted by rats and dogs. After 3 days, rats had excreted a mean of 92.4 and 5.6% of the dose in the urine and faeces respectively, and dogs had excreted a mean of 86.3 and 13.2% respectively. 5. After an oral dose of the cystein conjugate of [C]benzyl isothiocyanate, the major 14C-labelled metabolite in rat urine was the corresponding mercapturic acid (62% of the dose), whereas in dog urine it was hippuric acid (40% of the dose). 5. Mercapturic acid biosynthesis may be an important route of metabolism of certain isothiocyanates in some mammalian species.

[Studies of the metabolism and excretion of silybin in the rat]. / Untersuchungen zur Verstoffwechselung und zur Ausscheidung von Silybin bei der Ratte

The metabolism and excretion of silybin (as N-methyl-glucamine salt) was investigated after intravenous and oral administration to rats. In the urine, silybin was excreted mostly in the unchanged form after intravenous as well as oral application, whilst in the bile it appeared above all in the form of metabolites. By hydrolysis with arylsulfatase/beta-glucuronidase, the metabolites were identified as sulfate and glucuronide conjugates of silybin and dehyrosilybin; the latter appeared in small quantities as a dehydrated product of silybin. After intravenous injection of 20 mg silybin per kg body weight, the excreted amount of silybin after 48 h was 8%, whereas 76% was eliminated in the bile within the same period of time. After oral application of 2--20 mg silybin/kg body weight 20% after 40 mg/kg 35% and after 120 mg/kg 20% of the administered silybin was excreted in the bile during 48 h. The maximum excretion rate was achieved at application of 20 mg/kg p.o. after 1 h. At this dosage, 2--5% was eliminated within the same time in the urine. The excretion of silybin mainly took place (more than 80% of the total of excreted bilybin) in the bile, both after oral and intravenous administration.