Fate and distribution of 3H-labeled T-2 mycotoxin in guinea pigs

T-2 toxin is a potent cytotoxic metabolite produced by the Fusarium species. The fate and distribution of 3H-labeled T-2 toxin were examined in male guinea pigs. Radioactivity was detected in all body tissues within 30 min after an im injection of an LD50 dose (1.04 mg/kg) of T-2 toxin. The plasma concentration of trichothecene molar equivalents versus time was multiphasic, with an initial absorption half-life equal to or less than 30 min. Bile contained a large amount of radioactivity which was identified as HT-2, 4-deacetylneosolaniol, 3'-hydroxy HT-2, 3'-hydroxy T-2 triol, and several more-polar unknowns. These T-2 metabolites are excreted from liver via bile into the intestine. Within 5 days, 75% of the total radioactivity was excreted in urine and feces at a ratio of 4 to 1. The appearance of radioactivity in the excreta was biphasic. Metabolic derivatives of T-2 excreted in urine were T-2 tetraol, 4-deacetylneosolaniol, 3'-hydroxy HT-2, and several unknowns. These studies showed a rapid appearance in and subsequent loss of radioactivity from tissues and body fluids. Only 0.01% of the total administered radioactivity was still detectable in tissues at 28 days. The distribution patterns and excretion rates suggest that liver and kidney are the principal organs of detoxication and excretion of T-2 toxin and its metabolites.     

Pharmacokinetics of T-2 tetraol,a urinary metabolite of the trichothecene mycotoxin,T-2 toxin,in dog

1. The urinary metabolites of T-2 toxin were identified and analysed quantitatively after i.v. administration to dogs.

2. A new routine assay for T-2 tetraol was developed and a pharmacokinetic study was carried out on this final hydrolytic metabolite of T-2 toxin. T-2 tetraol was excreted in urine for 2–3 days. Its ‘sigma minus' plot demonstrated a significantly longer apparent half-life than its precursors (T-2 toxin and HT-2 toxin). This fact was explained by extraplasma binding causing prolongation of the metabolism and excretion of T-2 toxin metabolites.

3. The urinary metabolites of T-2 toxin were: HT-2 toxin, T-2 triol and T-2 tetraol. The metabolites were excreted in free and conjugated forms. In two dogs T-2 toxin was found in the urine in an amount which accounts for 3.2 and 16% of the administered dose respectively. The cumulative amount of the identified metabolites and toxins formed in the urine ranged from 9.7 to 17.3% in four dogs and 44.7% in one dog.     

Pharmacokinetics of T-2 tetraol, a urinary metabolite of the trichothecene mycotoxin, T-2 toxin, in dog

1. The urinary metabolites of T-2 toxin were identified and analysed quantitatively after i.v. administration to dogs. 2. A new routine assay for T-2 tetraol was developed and a pharmacokinetic study was carried out on this final hydrolytic metabolite of T-2 toxin. T-2 tetraol was excreted in urine for 2-3 days. Its 'sigma minus' plot demonstrated a significantly longer apparent half-life than its precursors (T-2 toxin and HT-2 toxin). This fact was explained by extraplasma binding causing prolongation of the metabolism and excretion of T-2 toxin metabolites. 3. The urinary metabolites of T-2 toxin were: HT-2 toxin, T-2 triol and T-2 tetraol. The metabolites were excreted in free and conjugated forms. In two dogs T-2 toxin was found in the urine in an amount which accounts for 3.2 and 16% of the administered dose respectively. The cumulative amount of the identified metabolites and toxins formed in the urine ranged from 9.7 to 17.3% in four dogs and 44.7% in one dog.     

Metabolism of T-2 toxin by rat brain homogenate

HT-2 toxin was the sole metabolite formed when T-2 toxin was treated with homogenate from brain without its blood content. Homogenate from brain with its full blood content produced--besides HT-2 toxin--T-2 triol, neosolaniol, 4-deacetylneosolaniol and T-2 tetraol, i.e. the same metabolites formed by incubation of T-2 toxin with whole rat blood.     

Metabolism and Clearance of T-2 Mycotoxin in Perfused Rat Livers

Metabolism and Clearance of T-2 Mycotoxin in Perfused Rat Livers.PACE, J.G. (1986). Fundam. Appl. Toxicol. 7, 424-433. Isolatedperfused rat livers were used to study the metabolism and clearanceof T-2 mycotoxin, a nonprotein Fusarium metabolite known tocause illness or death on contact or by ingestion. To evaluatethe in vitro hepatic metabolism, clearance, and rate of biliaryexcretion of T-2 toxin, [³H]T-2 toxin was delivered under constantperfusate flow (8 ml/min, 33.9 µg T-2/min) in a single-passexperiment. Steady-state conditions were achieved within 10min as indicated by a constant exit rate of radiolabel in theeffluent. At steady state, 93 ± 4% of the delivered [³H]T-2was extracted and metabolized by the liver, while 4.6 ±0.3% remained unmetabolized in the effluent perfusate. The excretionrate of metabolites and conjugates into bile was constant aftera 10-min perfusion. Radioactivity measured in bile accountedfor 55% of the total radiolabel delivered during the perfusionexperiment (1 hr). T-2 toxin was metabolized and eliminatedas 3Tiydroxy HT-2, 3Tiydroxy T-2 triol, 4-deacetylneosolaniol,T-2 tetraol, and glucuronide conjugates of HT-2, 3Tiydroxy HT-2,and T-2 tetraol. Approximately 7% of the administered radiolabelremained in the liver and was identified as 4-deacetylneosolaniol(18%), T-2 tetraol (41%), and conjugated metabolites (41%).Total recovery of administered radiolabel associated with T-2and its metabolites equaled 97.6% (bile, 52.5%; perfusate, 38.0%;liver, 7.1%). Approximately 3% of the biliary radiolabel wasnot identified. These studies describe the use of a perfusedorgan system to determine the rate of formation of T-2 metabolitesand their elimination into bile.     

Metabolism of T-2 toxin in vascularly autoperfused jejunal loops of rats

The intestinal metabolism of T-2 toxin, a major trichothecene mycotoxin, was investigated in rats using the method of the vascularly autoperfused jejunal loop in situ. Tritium-labeled T-2 toxin was injected into the tied-off intestinal segments at a dose of 5 or 500 nmol, respectively. T-2 toxin and its metabolites in the blood draining from the jejunal loops, in the intestinal lumen, and in the intestinal tissue were determined by HPLC and GLC-MS. There was an extensive metabolic degradation of T-2 toxin, the metabolite pattern being similar for the two dosage levels. During the experimental period of 50 min only some 2% of the total dose appeared in the effluent plasma as unchanged T-2 toxin. Likewise at the end of the experiments unchanged T-2 toxin in the intestinal lumen and tissue was present in minute amounts only (less than 1% of the dose). HT-2 toxin was the main metabolite. About 25% of the total radioactivity administered appeared in the effluent plasma as HT-2 toxin, 18% in the lumen and 10% in the tissue. 3'-OH-HT-2 toxin accounted for 4-7% (effluent plasma), 5% (lumen), and 2% (tissue) of the total dose. Furthermore small amounts (less than 2% of the dose) of 3'-OH-T-2 toxin, T-2 tetraol, and 4-deacetylneosolaniol were found. No glucuronide or sulfate conjugates could be detected. In the jejunal segments which had been exposed to the 5-nmol dose only minimal morphological alterations were observed. On the other hand, in jejunal segments exposed to the high dose marked tissue damage was present. Nevertheless the gut tissue retained its ability to metabolize T-2 toxin. From the present results it is concluded that T-2 toxin is subject to a marked presystemic first pass effect after oral ingestion in vivo.     

Human Biomonitoring of T-2 Toxin,T-2 Toxin-3-Glucoside and Their Metabolites in Urine through High-Resolution Mass Spectrometry

The metabolic profile of T-2 toxin (T-2) and its modified form T-2-3-glucoside (T-2-3-Glc) remain unexplored in human samples. Therefore, the present study aimed to investigate the presence of T-2, T-2-3-Glc and their respective major metabolites in human urine samples (n = 300) collected in South Italy through an ultra-high performance liquid chromatography (UHPLC) coupled to Q-Orbitrap-HRMS methodology. T-2 was quantified in 21% of samples at a mean concentration of 1.34 ng/mg Crea (range: 0.22–6.54 ng/mg Crea). Almost all the major T-2 metabolites previously characterized in vitro were tentatively found, remarking the occurrence of 3′-OH-T-2 (99.7%), T-2 triol (56%) and HT-2 (30%). Regarding T-2-3-Glc, a low prevalence of the parent mycotoxin (1%) and its metabolites were observed, with HT-2-3-Glc (17%) being the most prevalent compound, although hydroxylated products were also detected. Attending to the large number of testing positive for T-2 or its metabolites, this study found a frequent exposure in Italian population.     

Characterization of metabolites of benz(j)aceanthrylene in faeces,urine and bile from rat

1. The excretion of benz[j]aceanthrylene (B[j]A) and the biotransformation products found in faeces, urine and bile of rat exposed to [³H]-labelled B[j]A have been studied. 2. About 95% of the administered radioactivity was excreted within 7 days, 79% via faeces and 16% via urine, and most of the radioactivity in urine and faeces was excreted within 2 days. 3. The B[j]A metabolites excreted between days 1 and 2, including those excreted in bile during the first 5.5 h in a separate experiment, were further characterized by HPLC, UV and electrospray/atmospheric pressure chemical ionization mass spectrometry. 4. In faeces, bile and urine, hydroxylated B[j]A metabolites predominated. The major metabolites in faeces were B[j]A-1,2-dihydrodiol-8-hydroxy and B[j]A-1,2-dihydrodiol-10-hydroxy. These metabolites were found as conjugated metabolites in the bile. The glucuronide conjugate of B[j]A-1,2-dihydrodiol-10-hydroxy was also a major metabolite in urine. Two sulphate conjugates of oxidized B[j]A were detected in bile, a sulphate conjugate of a B[j]A-dihydrodiol-phenol and B[j]A-1,2-dihydrodiol-10-sulphate. Trans B[j]A-1,2-dihydrodiol was detected in urine, faeces and bile. 5. These findings support the hypothesis that epoxidation at the cyclopenta ring is an important biotransformation pathway for B[j]A in vivo. In addition to the characterized metabolites, a large fraction of polar compounds, possibly glutathione conjugates, was also excreted in urine and bile.     

Characterization of metabolites of benz(j)aceanthrylene in faeces, urine and bile from rat

1. The excretion of benz[j]aceanthrylene (B[j]A) and the biotransformation products found in faeces, urine and bile of rat exposed to [3H]-labelled B[j]A have been studied. 2. About 95% of the administered radioactivity was excreted within 7 days, 79% via faeces and 16% via urine, and most of the radioactivity in urine and faeces was excreted within 2 days. 3. The B[j]A metabolites excreted between days 1 and 2, including those excreted in bile during the first 5.5 h in a separate experiment, were further characterized by HPLC, UV and electrospray/atmospheric pressure chemical ionization mass spectrometry. 4. In faeces, bile and urine, hydroxylated B[j]A metabolites predominated. The major metabolites in faeces were B[j]A-1,2-dihydrodiol-8-hydroxy and B[j]A-1,2-dihydrodiol-10-hydroxy. These metabolites were found as conjugated metabolites in the bile. The glucuronide conjugate of B[j]A-1,2-dihydrodiol-10-hydroxy was also a major metabolite in urine. Two sulphate conjugates of oxidized B[j]A were detected in bile, a sulphate conjugate of a B[j]A-dihydrodiol-phenol and B[j]A-1,2-dihydrodiol-10-sulphate. Trans-B[j]A-1,2-dihydrodiol was detected in urine, faeces and bile. 5. These findings support the hypothesis that epoxidation at the cyclopenta ring is an important biotransformation pathway for B[j]A in vivo. In addition to the characterized metabolites, a large fraction of polar compounds, possibly glutathione conjugates, was also excreted in urine and bile.     

Metabolism of T-2 mycotoxin by cultured cells

T-2 mycotoxin is a small (i.e. mol. wt 466), non-protein toxin. We studied its metabolism in Chinese hamster ovary (CHO) cells, African green monkey kidney (VERO) cells, human fibroblasts and mouse connective tissue cells (L-929). Confluent cells were exposed to [3H]-T-2(0.01 micrograms/ml) for 1 hr at 37 degrees C. The toxin was removed, cells rinsed, and unlabeled culture media added for 4 hr (37 degrees C). Cell monolayers were extracted and media and cell extracts were spotted on thin-layer chromatography plates with known standards. Thin-layer plates were developed and scanned for radioactivity, and metabolites were identified based on co-migration with known standards. CHO and VERO cells metabolized T-2 to a greater per cent and to a wider variety of metabolites than the other two cell types. In CHO, fibroblast and L-929 cells, the major metabolite was HT-2 toxin, while in VERO cells an unknown metabolite, more polar than T-2, was the major metabolite. Cell and media extracts of CHO and VERO cells revealed smaller amounts of T-2 triol, T-2 tetraol and several unknowns. In both cell types, metabolites were detected in labeled media by 1 hr and in increasing amounts in unlabeled media by 4 hr. Under the above conditions, 37-58% of the radioactivity remained as T-2 toxin after 4 hr in both cell types. The data suggest that some cultured cell lines possess enzyme systems capable of limited metabolism of T-2 mycotoxin to a variety of known and some as yet unidentified metabolites.     

Enterohepatic circulation of T-2 toxin metabolites in the rat

The enterohepatic circulation of T-2 toxin and its conjugated metabolites was examined in bile duct-cannulated male rats. Rats administered tritiated T-2 toxin intraduodenally (id) eliminated 44.65% and 57.25% of the administered dose in the bile within 4 and 8 hr post-dosing, respectively. TLC profiles of the T-2 metabolites were similar after intravascular and id administration. The major metabolites detected were 3'-OH-hydroxytryptamine-2 (HT-2), glucuronic acid conjugates, T-2 tetraol (TOL), 4-deacetylneosolaniol (4-DN), and HT-2. Tritium-labeled glucuronides obtained from the bile of rats administered [3H]T-2 toxin intravascularly were extracted and purified using C-18 and silica column chromatography. Enzymatic hydrolysis followed by TLC and GC/MS indicated that the aglycone portion of the glucuronides were composed of 3'-OH HT-2, HT-2, 4-DN, and TOL. After id administration of the glucuronides the rats eliminated 6.01% (4 hr) and 11.86% (8 hr) of the dose in the bile. No free metabolites of T-2 toxin were detected in the bile of any animals administered the purified glucuronides. Oral treatment of the rats with the beta-glucuronidase inhibitor, saccharolactone, did not produce a significant decline in the amount of radioactivity recovered in the bile following administration of the tritium-labeled glucuronides. These studies substantiate the enterohepatic circulation of T-2 toxin metabolites.     

Hepatic subcellular distribution of [H]T-2 toxin

and . Hepatic subcellular distribution of [³H]T-2 toxin. Toxicon 27, 1307–1311, 1989.—The subcellular distribution of T-2 mycotoxin and its metabolites was studied in isolated rat livers perfused with [³H]T-2 toxin. After a 120-min perfusion, the distribution of radiolabel was to bile 53%, perfusate 38% and liver 7%. Livers were fractionated into mitochondria, endoplasmic reticulum (smooth and rough), plasma membrane and nuclei. Plasma membrane fractions contained 38% of the radiolabel within 5 min, decreasing to < 1% at the end of the 120-min perfusion. Smooth endoplasmic reticulum contained 27% of the radiolabel by 5 min and increased to 43% over the 120-min perfusion. The mitochondrial fraction contained 3% of the radiolabel by 30 min and increased to 10% after 120-min perfusion. Label in the nuclear fraction remained constant at 7% from 30 to 120 min. By 15 min, only the parent toxin was detected in the mitochondrial fraction. In the other fractions, radiolabel was associated with HT-2, 4-deacetylneosolaniol, T-2 tetraol, and glucuronide conjugates. Glucuronide conjugates accounted for radiolabel eliminated via the bile. The time course for distribution of radiolabel in liver suggested an immediate association of [³H]T-2 with plasma membranes and a subsequent association of toxin and metabolites with endoplasmic reticulum, mitochondria and nuclei, the known sites of action of this toxin.     

Biomonitoring of Multiple Mycotoxins in Urine by GC–MS/MS: A Pilot Study on Patients with Esophageal Cancer in Golestan Province,Northeastern Iran

A pilot study to investigate the occurrence of 10 mycotoxins (deoxynivalenol, DON; 3-acetyldeoxynivalenol, 3-ADON; 15-acetyldeoxynivalenol, 15-ADON; fusarenon-X, FUS-X; diacetoxyscirpenol, DAS; nivalenol, NIV; neosolaniol, NEO; zearalenone, ZON; zearalanone, ZAN; T-2 toxin, T-2; and HT-2 toxin, HT-2) in esophageal cancer patients was performed with the urinary biomarkers approach in Golestan, Iran. Urine multimycotoxin analysis was performed by dispersive liquid–liquid microextraction and gas chromatography–tandem mass spectrometry (GC–MS/MS) analysis, and values were normalized with urinary creatinine (μg/g). Four mycotoxins, namely NEO (40%), HT-2 (17.6%), DON (10%), and HT-2 (5.8%), were detected in the analyzed urine samples. DON was only detected in the control group (5.09 μg/g creatinine), while T-2 (44.70 μg/g creatinine) was only present in the esophageal cancer group. NEO and HT-2 were quantified in both control and case groups, showing average of positive samples of 9.09 and 10.45 μg/g creatinine for NEO and 16.81 and 29.09 μg/g creatinine for HT-2, respectively. Mycotoxin co-occurrence was observed in three samples as binary (NEO/HT-2 and T-2/HT-2) and ternary (DON/NEO/HT-2) combinations, reaching total concentrations of 44.58, 79.13, and 30.04 µg/g creatinine, respectively. Further investigations are needed to explore a causal association between mycotoxin contamination and esophageal cancer. For this pilot study in Golestan, the low sample size was a very limiting factor.     

Determination of T-2 and HT-2 Toxins in Seed of Milk Thistle [Silybum marianum (L.) Gaertn.] Using Immunoaffinity Column by UPLC-MS/MS

Milk thistle [Silybum marianum (L.) Gaertn.] achieved a significant increase in interest over the past few years from local and foreign pharmaceutical corporations. The silymarin complex of constituents extracted from milk thistle achenes provides compelling health benefits primarily thanks to antioxidant activities and hepatoprotective effects. However, consuming mycotoxin-contaminated plant material can cause immunosuppression and hepatotoxic problems. The aim of this study was to develop and validate a method for the determination of mycotoxin content in milk thistle. Fusarium toxins as T-2 and HT-2 toxins in grown milk thistle harvested from a breeding station in the Czech Republic during 2020–2021 were studied. The analysis of T-2 and HT-2 toxins was performed by UPLC-MS/MS after immunoaffinity columns EASI-EXTRACT^® T-2 & HT-2 clean up. All analysed samples of milk thistle were contaminated with T-2 toxin and HT-2 toxin. The content of T-2 toxin in the samples from 2020 was in the range of 122.7–290.2 µg/kg and HT-2 toxin 157.0–319.0 µg/kg. In 2021, the content of T-2 toxin was in the range of 28.8–69.9 µg/kg and HT-2 toxin was 24.2–75.4 µg/kg. The results show that the climatic conditions of the year of harvesting have a highly statistically significant effect on the content of T-2 and HT-2 toxins in milk thistle.     

Isolation and identification of metabolites of 2-ethylhexyl diphenyl phosphate in rats

The metabolic fate of 2-ethylhexyl diphenyl phosphate (EHDPP) was studied in male rats. Orally administered ¹⁴C-EHDPP was rapidly absorbed and about 80% of the radioactivity was excreted in the urine and feces in the first 24 h. By 7 days, 48% and 52% of the radioactivity was recovered in urine and feces, respectively. Since biliary excretion was low (6% for 2 days), urine seems to be the major excretion route of EHDPP. Radioactivity was widely distributed in all tissues examined. At 2 h, the concentration was relatively high in blood, liver kidney and adipose tissue. The elimination of radioactivity from adipose tissue and liver was somewhat delayed, but almost all the radioactivity was eliminated by 7 days. The major metabolites in the urine were diphenyl phosphate (DPP) and phenol. p-Hydroxyphenyl phenyl phosphate (OH-DPP) and monophenyl phosphate (MPP) were also identified as minor metabolites.     

DOSE-DEPENDENT EFFECTS ON THE DISPOSITION OF MONOMETHYLARSONIC ACID AND DIMETHYLARSINIC ACID IN THE MOUSE AFTER INTRAVENOUS ADMINISTRATION

The organic arsenicals monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) are the primary metabolites of inorganic arsenic, a known human carcinogen. The objective of this study was to examine if dose would affect the excretion and terminal tissue disposition of MMA and DMA in the mouse. 14C-MMA (4.84 and 484 mumol/ kg) and-DMA ( 8.04 and 804 mumol/kg) were administered to female micevia the tail vein. The mice were placed in metabolism cages for collection of urine (1, 2, 4, 8, 12, and 24 h) and feces ( 24 h) . The animals were then sacrificed at 24 h and tissues were removed and analyzed for radioactivity. The urine was also analyzed for parent compound and metabolites. Urinary excretion of MMA- and DMA-derived radioactivity predominated over fecal excretion. Dose did not affect the overall urinary excretion of both compounds. However, fecal excretion was significantly lower in the low-dose MMA-treated animals as opposed to in the high-dose group, whereas in the high-dose DMA-treated group excretion was lower than in the low-dose DMA group. The retention of radioactivity was low ( &lt;2% of dose) and the distribution pattern similar for both compounds, with carcass &gt; liver &gt;kidney &gt; lung. The concentration of radioactivity (% dose/ g tissue) was greater in kidney than in liver, lung, and blood for both compounds. The distribution and concentration of MMA-derived radioactivity was significantly greater in the liver and lung of the high-dose group. The MMA-treated animals excreted predominantly MMA in urine and lower amounts of DMA (&lt;10% of the dose). The percentage excreted as DMA was significantly higher in the low-dose MM A group. In the urine of DMA-treated anim als, an unstable metabolite and the parent compound were detected. Overall, it appears the dose of organic arsenical administered has a minimal effect on its excretion and terminal tissue disposition in the mouse. The rapid elimination and low retention of MMA and DMA explain in part their low acute toxicity.     

Disposition and metabolism of 2-bromo-4,6-dinitroaniline in the male F344 rat

The disposition of [14C]-2-bromo-4,6-dinitroaniline (BDNA) was studied in male F344 rats following oral or intravenous (iv) administration. The gastrointestinal absorption of BDNA was nearly complete and was not affected by dose in the range (10-100 mumol/kg body weight) studied. Following either oral or iv administration, BDNA was rapidly distributed throughout the tissues and showed no marked affinity for any particular tissue. Clearance of [14C]BDNA-derived radioactivity from various tissues was rapid and was best described by two-component decay curves. The whole-body half-life of BDNA was approximately 7 h. Within 72 h, clearance of [14C]BDNA-derived radioactivity from the body was 98% complete. [14C]BDNA was rapidly cleared by metabolism to 13 metabolites, which were excreted in urine (62%) and feces (33%). Most (66%) of the urinary radioactivity was excreted in the form of sulfate conjugates of two metabolites of BDNA; excretion of unmetabolized BDNA was minimal (less than 2%). Biliary excretion of [14C]BDNA was significant; however, some of this BDNA-derived radioactivity underwent enterohepatic circulation and was subsequently excreted in urine. Results of this study indicate that, if metabolism is a detoxification process, the rapid metabolism and excretion of this compound should minimize the likelihood of chronic toxicity from repeated exposure to BDNA beyond that predicted by data from acute or short-term exposures.     

Metabolism is an Important Route of Pentamidine Elimination in the Rat: Disposition of 14C-Pentamidine and Identification of Metabolites in Urine Using Liquid Chromatography-Tandem Mass Spectrometry

Abstract: This study assesses the contribution of metabolism for the disposition of pentamidine in the rat. With the use of ¹⁴C-labelled compound, the excretion of radioactivity in urine and faeces has been studied in four rats during 44 days after a single intravenous injection of the drug. The urinary and faecal excretion of the radioactivity were of equal importance; 22±2% (mean±S.D.) and 25±4% being detected in urine and faeces, respectively. The activity in organs and tissues at 44 days after drug administration was also measured and amounted to 21±5% of the administered dose. Using HPLC the proportion of metabolites in urine in relation to unchanged pentamidine increased with time after dose, being 76±15% (mean±S.D.) of the total excreted radioactivity on day 1 and 97±1% on day 6. HPLC - tandem mass spectrometry was used for identification of metabolites in urine obtained from four rats given unlabelled pentamidine. Using synthetic reference compounds and the selective MS/MS mode four oxidized metabolites of pentamidine were identified either by direct injection into the system or by analyses of extracted urine. Thus, a substantial part of pentamidine is excreted as metabolites in urine.     

Metabolism of the platelet-activating factor antagonist (±)-trans-2-(3′-methoxy-5′-methylsulphonyl-4′-propoxyphenyl)-5-(3″, 4″,5″-trimethoxyphenyl)tetrahydrofuran (L-659,989) in rhesus monkeys

1. The plasma concentration, main route of metabolism and excretion of ³H-L-659,989 were studied in male and female rhesus monkeys by dosing either i.v. or orally at 10 mg/kg.

2. The percentage of the AUC for the plasma radioactivity concentration-time curve of oral vs i.v. dosed monkeys was 78% for males and 90% for females, indicating that the dose was well absorbed.

3. The bioavailability of the drug was low (≤10%) for all monkeys, probably due to rapid first pass metabolism. The drug was metabolized predominantly at the C-4′-propoxy side-chain. The two major plasma metabolites were identified as the 4′-2-(hydroxy)propoxy metabolite (³H-trans-4′-HP) and the 4′-hydroxy metabolite (³H-4′-hydroxy) which was isolated as a 2:1 mixture of (±)trans:(±)cis.

4. Approx, 80% of the radiolabelied dose was excreted equally in the urine and faeces in 96h, with the largest percentage of the Initiated dose (31.4%) in the 0-24h urine.

5. The major metabolites in the excreta were the (±)trans(±)cis mixture of ³H-4′-hydroxy and the glucuronide conjugate of ^3H-trans-4′-hydroxy. The glucuronide conjugate of ³H-trans-4′-hydroxy was excreted in the urine of i.v. and orally dosed monkeys and represented an average of 21% and 5.1% of the dose, respectively. ³H-4′-Hydroxy was excreted in both the urine and faeces, accounting for. 0.1% and 7.4% of the dose in i.v. and orally dosed monkeys, respectively.     

Pharmacokinetics and metabolism of digoxigenin-mono-digitoxoside in man

Summary ³H-digoxigenin-mono-digitoxoside 1 mg was swallowed by 6 healthy subjects. Maximum plasma levels of radioactivity were reached within 1–2 h; in two subjects there was a second peak at 8–12 h. No definite half lives could be determined because the falls in plasma activity were not exponential. 3.9–39% and 34.5–76.6% of the dose were eliminated in urine and faeces, respectively. 75–90% of the total radioactivity in plasma was CHCl₃-insoluble, there was less of this fraction in urine, and the major portion in faceces was CHCl₃-soluble. The CHCl₃-insoluble fraction in urine was separated into 3 components by chromatography on an Al₂O₃-column and consisted mainly of conjugates of the monoglycoside and 3-epidigoxigenin. TLC-separation of the lipophilic fraction in urine also revealed unchanged monoglycoside and 3-epidigoxigenin, as well as traces of digoxigenin, 3-ketodigoxigenin and 2 unidentified, more polar metabolites. In faeces, the main excretion product was the unchanged compound, and traces of digoxigenin, 3-epidigoxigenin, 3-ketodigoxigenin and one of the more polar metabolites detected in urine. Two patients with surgical T-tube bile-duct drainage showed significantly greater biliary excretion after oral administration of the digoxigenin-mono-digitoxoside than after digoxin. Almost all the radioactivity excreted in bile was CHCl₃-insoluble and the monoglycoside was shown to be the only conjugation partner present by incubation with arylsulfatase and -glucuronidase. The results show that digoxigenin-mono-digitoxoside has such a rapid metabolic inactivation and biliary clearance in man that it is unlikely to be of any therapeutic value.This study was supported by the Deutsche Forschungsgemeinschaft.