Analysis in the rat of 4-hydroxynonenal metabolites excreted in bile: evidence of enterohepatic circulation of these byproducts of lipid peroxidation

4-Hydroxynonenal (HNE) is a cytotoxic product resulting from the lipid peroxidation of membrane polyunsaturated fatty acids. In vitro, metabolism mainly leads to the corresponding alcohol (DHN), carboxylic acid (HNA), and the glutathione conjugate, whereas in vivo, mercapturic acid conjugates of HNE, DHN, HNA, and HNA-lactone and, more recently, dicarboxylic acids and related mercapturate conjugates were identified in urine of rats. In the study presented here, the identity of the HNE biotransformation products in the bile of rats following a single iv administration of [4-(3)H]HNE and the potential for enterohepatic recycling of HNE metabolites were investigated. The identity of metabolites was assessed by comparison of their HPLC retention times with those of the corresponding synthesized standards and by mass spectrometry analysis. Five metabolites were present in the bile; two of them corresponded to HNE- and DHN-glutathione conjugates. Two others metabolites were identified as DHN- and HNA-lactone mercapturic acid conjugates. The fifth metabolite was isolated but remained unidentified. As previously observed for urinary elimination, the kinetic excretion of biliary metabolites exhibited a rapid metabolism of HNE in rats. Within 4 h of injection, the bile accounted for 19.5% (+/-2.8%) of the injected radioactivity, whereas only 3% was found in the feces within 48 h [Alary, J., et al. (1995) Chem. Res. Toxicol. 8, 34-39]. The extent of HNE enterohepatic recycling was estimated utilizing a modified version of the linked rat model in three animals. All rat recipients were found to have measurable levels of HNE metabolites in bile, confirming that HNE is likely to undergo enterohepatic recirculation in the rat. The extent of recycling was approximatly 7. 7% of the total dose in this model. Two unknown metabolites were present in the bile of recipient rats and not found in the bile of donors rats, suggesting that intestinal microflora and/or intestinal mucosa could biotransform HNE-related compounds before or during the reabsorption process.

Urinary metabolites of 4-n-nonylphenol in rainbow trout (Oncorhynchus mykiss)

Nonylphenol is present in surface water and aquatic sediments and because of its lipophilic characteristics shows a considerable potential to bioaccumulate in aquatic organisms. Nonylphenol inhibits testicular growth and induces vitellogenin synthesis in male rainbow trout. In order to better understand the effects of nonylphenol on fish and its impact in the aquatic environment, it is essential to elucidate the metabolic fate of this compound. A single oral dose (5 mg, 1850 KBq) of [3H]4-n-nonylphenol resulted in 1.1% and 3.0% of the ingested radioactivity eliminated in urine after 24 and 48 h, respectively. Four metabolites were separated by radio-HPLC and tentatively identified by mass spectrometry. Urinary metabolites likely resulted from the initial omega-oxidation of 4-n-nonylphenol to the putative 9-(4-hydroxyphenyl)-nonanoic acid which subsequent beta-oxidation led to 4-hydroxybenzoic acid as major metabolite. Intermediary metabolites, namely 3-(4-hydroxyphenyl) propionic acid and 3-(4-hydroxyphenyl)-2-propenoic acid confirmed the occurrence of this beta-oxidative pathway. Urinary metabolites identified in this study were quite different from biotransformation products previously described in bile of trout treated with 4-n-nonylphenol.

Urinary and biliary metabolic patterns of chlorothalonil in germ-free and conventional rats

The metabolic fate of chlorothalonil, a broad spectrum fungicide that is known to be metabolized via glutathione conjugation, was examined through the analysis of urine and bile metabolites. The role of digestive microflora in the metabolism of chlorothalonil was assessed by comparing the metabolic patterns in germ-free and conventional rats. Low urinary and biliary excretion of radioactivity was observed in both conventional and germ-free rats. However, the urinary excretion of radioactivity was higher in conventional than in germ-free rats. Radio-HPLC analysis of urine and bile showed a complex metabolic profile in both conventional and germ-free rats. Methylthio metabolites of chlorothalonil were determined in ethyl acetate extracts of urine and bile of conventional and germ-free rats. These metabolites were excreted in a higher amount in the urine of conventional rats than in the urine of germ-free rats. This study shows the complexity of chlorothalonil metabolism and the role of the digestive microflora in chlorothalonil metabolism.

Biotransformation of pentachlorophenol, aniline and biphenyl in isolated rainbow trout (Oncorhynchus mykiss) hepatocytes: comparison with in vivo metabolism

1. The biotransformation of pentachlorophenol (PCP), aniline and biphenyl in rainbow trout (Oncorhynchus mykiss) isolated liver cells was investigated to examine if fish hepatocytes represent a suitable alternative to the in vivo approach for studying the biotransformation of chemicals. Each compound was incubated at two concentrations (10 and 60 microM) for 2 h. For comparison, the metabolic profile of these xenobiotics was also studied in urine and bile of trout orally exposed to 1.8-4.0 mg/kg wet wt of each compound. 2. In vitro as in vivo, PCP glucuronide and to a lesser extent PCP sulphate were the metabolites formed by trout from PCP. 3. Aniline was mainly metabolized to acetanilide and to a lesser extent to 2-aminophenol by isolated hepatocytes, but neither hydroxylated acetanilide nor conjugates were found in vitro whereas they were present in bile and urine of trout treated with this chemical. 4. Trout hepatocytes metabolized biphenyl to hydroxylated and dihydroxylated products and the corresponding glucuronides. These results correlated well with the metabolic profile obtained from the bile of trout exposed to this pesticide. 5. It is concluded that although hepatocytes are well suited for several types of biotransformation studies, the fact that this system may in some cases produce a different metabolic pattern than in vivo should be considered when attempting to extrapolate in vitro to in vivo data.

Cytochrome P450-dependent metabolic pathways and glucuronidation in trout liver slices

We investigated the capacity of trout precision-cut liver slices to metabolize xenobiotics and steroids. As a first approach, liver slices were compared with freshly isolated trout hepatocytes, using 7-ethoxycoumarin (7-EC) and testosterone as substrates. Trout liver slices and freshly isolated hepatocytes had a similar capacity for conducting cytochrome P450-dependent metabolism, as indicated by the rate of oxidative metabolism of 7-EC and testosterone, and by the metabolic profile of these substrates. A lower rate of glucuronidation in slices compared with hepatocytes was observed with testosterone (50 microM), whereas the opposite situation occurred with 7-EC used at higher concentration (100 microM). In a second step, we investigated the effect of beta-naphthoflavone on 7-EC and testosterone biotransformation, using slices maintained in culture for 24 h, with or without the inducer added. The results were compared with the metabolic rates of these substrates incubated with liver slices originating from trout pretreated in vivo with beta-naphthoflavone. Cytochrome P450-mediated rates of 7-EC dealkylation and testosterone hydroxylation decreased to 38 and 55% of the control value, respectively, when incubations were performed in 24-h cultured slices instead of freshly cut slices. Exposure of the slices to 50 microM beta-naphthoflavone resulted in about 3 times higher deethylation rate of 7-EC. A similar value was obtained when treatment occurred in vivo. As demonstrated in rat by several authors, liver slices seem a useful and simple tool for studying the metabolic pathways of xenobiotics and steroids and for the assessment of inducers of the CYP1A1 family.

Ex vivo gastrointestinal biotransformation of chlorothalonil in the germ-free and conventional rat

1. The metabolism and absorption of chlorothalonil and corresponding diglutathione and dicysteine conjugates was studied using isolated everted gastrointestinal sacs of the conventional and germ-free rat. An HPLC method was used to analyse mucosal and serosal fluids. Thiol metabolites of chlorothalonil were determined by GC/MS. 2. Low absorption of the substrates was observed, with < 4% of the radioactivity being recovered from the serosal buffers and the digestive tissues. A major part of the radioactivity was recovered from the mucosal fluids and it corresponded to unchanged chlorothalonil. Traces of unchanged chlorothalonil and mono-, di- and trimethylthio metabolites were present in serosal fluids as well as unidentified polar peaks. An important transformation (> 75%) of the chlorothalonil conjugates was observed. The di- and trimethylthio metabolites of chlorothalonil were detected from both sides of the everted gut sac of rat incubated with the diglutathione and dicysteine conjugates. 3. Few differences were observed between the conventional and germ-free rat: absorption was higher in the duodenum of germ-free rat, but tissue retention was more significant in the duodenum of the conventional rat.

Identification of novel urinary metabolites of the lipid peroxidation product 4-hydroxy-2-nonenal in rats

Following iv administration of 4-hydroxy-2-nonenal (HNE) and [4-3H]HNE to rats, 15 polar urinary metabolites accounting for about 50% of the urinary radioactivity were separated by HPLC. Among them, eight major compounds and tritiated water were quantified. The metabolites were unequivocally characterized using GC/MS and ESI/MS/MS/MS. Most of "HNE polar metabolites" originate from omega-oxidation of 4-hydroxy-2-nonenoic acid (HNA): 9-hydroxy-HNA, its mercapturic acid conjugate, and two diastereoisomers of the corresponding lactone. The oxidation of 9-hydroxy-HNA by alcohol and aldehyde dehydrogenases leads to the excretion of 9-carboxy-HNA and of the corresponding lactone mercapturic acid conjugate. 1, 4-Dihydroxy-2-nonene (DHN) originating from the reduction of HNE by alcohol dehydrogenase was to a lesser extent omega-hydroxylated, leading to 9-hydroxy-DHN which was excreted as a mercapturic acid conjugate (two diastereoisomers).

Characterization of biliary metabolites of 4-n-nonylphenol in rainbow trout (Oncorhynchus mykiss)

1. [R-2,6-3H]-4-n-nonylphenol was synthesized and a single dose (5 mg, 1850 KBq) orally administered to rainbow trout. After 48 h, the radioactivity present in the bile amounted 5.5%. More than ten biliary metabolites were separated by hplc and collected for subsequent mass spectrometry analysis. The metabolic profile was totally modified by beta-glucuronidase hydrolysis, showing that most of the metabolites were glucuronic acid conjugates. 2. Conjugated metabolites were identified by lc-ms analysis and their aglycones were analysed by gc-ms analysis as TMS and acetyl derivatives. 3. The major metabolite accounted for 52+/-11% of the biliary radioactivity and was identified as nonylphenol-glucuronide. 4. Nonylphenol was hydroxylated at both omega and omega-1 positions of the alkyl chain, giving 9-hydroxynonylphenol and 8-hydroxynonylphenol. 5. 9-Hydroxynonylphenol was oxidized to the corresponding acid, and subsequently beta-oxidized, yielding 7-(4-hydroxyphenyl)heptanoic acid, 5-(4-hydroxyphenyl)pentanoic acid, 3-(4-hydroxyphenyl)propionic acid and 3-(4-hydroxyphenyl)-2-propenoic acid.

1,4-Dihydroxynonene mercapturic acid, the major end metabolite of exogenous 4-hydroxy-2-nonenal, is a physiological component of rat and human urine

In the present study 1,4-dihydroxynonene mercapturic acid (DHN-MA), previously shown to be the major urinary metabolite of 4-hydroxy-2-nonenal (HNE) administered to the rat, was characterized and determined to be a normal constituent of rat and human urine. DHN-MA was excreted as a mixture of at least two stereoisomers as determined by ion trap LC-MS/MS/MS after solid-phase extraction and HPLC purification. The 24-h urinary excretion of this compound was about 10 ng and 5 microg for rat and human, respectively. This end metabolite of the lipid peroxidation product HNE could represent a specific and noninvasive biomarker.

Influence of growth hormone on the hepatic mixed function oxidase and transferase systems of rainbow trout

The effect of GH treatment on hepatic cytochrome P450 content, aryl hydrocarbon hydroxylase (AHH), aminopyrine-N-demethylase (AND), testosterone hydroxylase, testosterone 5α- and 5β-reductase, UDP-glucuronyl transferase (UDPGT) and glutathione S-transferase (GST) activities in immature rainbow trout were investigated. Hepatic cytochrome P450 content, AHH and GST activities were measured in both GH implanted and GH injected animals whereas other activities were assayed in GH implanted trout only.GH implants significantly decreased cytochrome P450 content at 15 days compared to the control but no significant effect was observed at 15 or 30 d when GH was injected biweekly. In both cases, AHH activity was significantly decreased by GH treatment compared to the control whereas GST remained unchanged. Compared to the control, GH implanted fish exhibited a pronounced inhibition of AND, a decreased 6β and 16β-testosterone hydroxylation, an inhibition of UDPGT with testosterone as substrate and an enhanced 17β-testosterone oxidation.

Chloramphenicol oxamylethanolamine as an end product of chloramphenicol metabolism in rat and humans: evidence for the formation of a phospholipid adduct

Chloramphenicol (CP) has been implicated as, although not proven to be, a causative agent of aplastic anemia in humans. Recent studies from our laboratory have presented evidence that CP-oxamylethanolamine was an end product of CP biotransformation in birds. Because this novel metabolic pathway has never been reported in other species, we have now expanded these investigations to rat and humans. [3H]CP was administered po (10 mg/kg) to adult male Wistar rats and to a human volunteer. Urine was collected and analyzed by HPLC and GC-MS for CP metabolite determination. In rat, the two most important metabolites in 0-24 h urine were CP-base and CP-acetylarylamine which together accounted for about 50% of the ingested radioactivity. The remainder was due to unchanged CP, CP-oxamic acid, CP-alcohol, CP-glucuronide, and CP-oxamylethanolamine. The presence of these end products was also demonstrated in man. CP-oxamylethanolamine represented 0.74% and 1.37% of the ingested radioactivity in rat and human urine samples, respectively. CP-oxamylethanolamine formation was confirmed in vitro with isolated rat hepatocytes, suggesting the involvement of liver in the production of this metabolite. The origin of CP-oxamylethanolamine has been investigated with the use of hepatic liver microsomes from phenobarbital-treated rats. The incubation of [3H]CP with this subcellular fraction led to the binding of a radiolabeled compound to the microsomal lipids, whereas no binding occurred when CP-oxamic acid was incubated with the microsomes. Enzymatic hydrolysis of the microsome lipid fraction with phospholipase D from Streptomyces chromofuscus released CP-oxamylethanolamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Mercapturic acid conjugates as urinary end metabolites of the lipid peroxidation product 4-hydroxy-2-nonenal in the rat

4-Hydroxy-2-nonenal (HNE), an aldehyde end product of lipid peroxidation in biological systems, is capable of producing a range of powerful biological effects. Despite its biological relevance, the metabolic fate of this aldehyde is unknown in vivo. This study examines the urinary excretion of HNE in the rat and the nature of metabolites formed. Following iv administration of [3H]HNE, the majority of the dose appeared in urine (67.1% after 48 h). The radio-HPLC metabolic profile showed that no unchanged parent compound was detected in urine whereas at least four metabolites were present, most of them corresponding to mercapturic acid conjugates. Two major pathways were involved in the biotransformation of HNE in vivo: (i) reduction/oxidation of the aldehyde group, and (ii) conjugation to endogenous glutathione leading to mercapturic acid conjugates in urine. These end products were isolated by HPLC and identified by mass spectrometry as HNE mercapturic acid, 1,4-dihydroxynonene mercapturic acid, 4-hydroxynonenoic mercapturic acid, and the corresponding lactone.

Biotransformation enzyme activities in the olfactory organ of rainbow trout (Oncorhynchus mykiss). Immunocytochemical localization of cytochrome P4501A1 and its induction by β-naphthoflavone

Olfaction is a crucial function in most fish species, but little is known about biotransformation enzymes in the olfactory organ. This study demonstrates that biotransformation enzymes usually found in the rainbow trout liver, are present in the olfactory organ as well. While microsomal cytochrome P450 reductase, p-nitrophenol hydroxylase and cytosolic glutathioneS-transferase presented similar levels in both the olfactory organ and the liver, microsomal 7-ethoxyresorufinO-deethylase (EROD), 7-ethoxycoumarinO-deethylase, and 7-pentoxyresorufinO-deethylase were much lower in the olfactory organ (77-, 35-, 200-times respectively). Furthermore, microsomes from the olfactory organ were able to perform testosterone hydroxylation only in the 16α-position while testosterone was hydroxylated in the 16β-position by liver microsomes. Using polyclonal antibodies raised against perch cytochrome P4501A1, the immunoreactive protein was shown to be strongly expressed in various cellular types forming the nonsensory epithelium. Some immunostaining was also reported in the nonsensory cellular elements constituting the sensory epithelium, while olfactory receptor cells failed to show cytochrome P4501A1-immunoreactivity. Finally, the exposure of rainbow trout to waterborne β-naphthoflavone (0.1 μg ml(-1)) for 2 or 4 days resulted in a higher induction of EROD activity in the olfactory organ compared to the liver. The presence of biotransformation enzymes in the olfactory organ of rainbow trout addresses the question of their involvement in the detoxication/toxication of pollutants as well as in the olfactory function.

Evidence for new metabolic pathways of chloramphenicol in the duck

Following subcutaneous administration of [3H]chloramphenicol (CP) to duck, HPLC and TLC analyses showed that the two most important metabolites in 0- to 24-hr excreta were CP-oxamic acid and CP-alcohol, which together accounted for about one-third of the radioactivity therein. The remainder was due to unchanged CP (15% dose), CP-base (5% dose), and various metabolites representing < 4% dose each. Among these, CP-glucuronide and CP-sulfate have been previously isolated in mammals. In addition to these metabolites, several previously unreported in vivo CP biotransformation products were identified in this study by HPLC and MS comparison with synthetic reference compounds. These new metabolites were unequivocally identified as 1-O-monoacetyl CP, CP-1,3-diacetate, N-acetyl CP-base, CP-oxamylglycine, and CP-oxamylethanolamine. Besides these formally identified compounds, the CP-phosphate structure was tentatively assigned to a conjugate metabolite resistant to beta-glucuronidase and sulfatase hydrolysis. The possible origin of these metabolites is discussed extensively.

Detection and characterization of a novel hepatic 8 S binding protein for benzo[a]pyrene distinct from the Ah receptor

Using fractionation procedures such as sucrose gradient sedimentation and gel permeation chromatography, a novel cytosolic binding protein for benzo[a]pyrene has been detected in liver of nonmammalian and mammalian species including human. This protein, called 8 S protein, cosediments with the Ah receptor after centrifugation in sucrose density gradient but can be separated from the Ah receptor and 4 S protein by gel permeation chromatography. Owing to its binding characteristics, the 8 S protein is clearly distinct from the Ah receptor. The [3H]BP binding parameters have been determined by saturation experiments. According to Scatchard and Woolf plots the Kd are 268 nM and 138 nM for DBA/2 mouse and guinea pig 8 S proteins, respectively. Bmax are 248 and 840 pmol/mg for DBA/2 mouse and guinea pig 8 S proteins, respectively. Apparent molecular mass of 8 S protein, according to Stokes radius (5 +/- 0.2 nm) and sedimentation coefficient, was estimated approximately 170,000 +/- 6000. After in vitro incubation of 8 S proteins with [3H]BP the charcoal, as well as the 4 S protein, exerts potent stripping effects on the [3H]BP binding. In contrast, after administration of [3H]BP to DBA/2 mice the 8 S protein-[3H]BP complex formed in vivo is more resistant to the stripping effects of charcoal and 4 S protein. Competition studies demonstrate that polycyclic aromatic hydrocarbons (PAHs) (BP > 1-aminopyrene > pyrene > 7,12-dimethylbenz[a]anthracene > 3-methylcholanthrene > benzo[e]pyrene > benzo[g, h, i,]perylene) are the best ligands of the 8 S protein. In contrast, the 2,3,7,8-tetrachlorodibenzo-p-dioxin is a poor ligand of this protein. Phenobarbital, steroid hormones, and omeprazole don't bind the 8 S protein. The at present unknown function of the 8 S protein and its role in the toxicology of PAHs are currently under investigation.

Biotransformation and branchial excretion of 17 alpha-methyltestosterone in trout

This study was designed to characterize the branchial excretion of 17 alpha-methyltestosterone (17MT) metabolites in rainbow trout (Oncorhynchus mykiss). Spinally transected trout were force-fed 0.4 mg/kg [1,2-3H]17MT and the branchial, fecal, and urinary excreta were collected during 24 hr. Branchial elimination was the primary route of excretion, because it contributed to 68% of the excreted radioactivity within 24 hr after ingestion. The radio-HPLC metabolic profile obtained from branchial excreta showed that 17MT was partly eliminated across the gills as parent compound. In addition to unchanged 17MT, several unconjugated metabolites have been isolated and identified by GC/MS. Two major pathways were involved in the biotransformation of 17MT: hydroxylation and/or reduction of the androstene structure. Reduction of the 4-ene functionality leading to the formation of methyldihydrotestosterone and its further reduction leading to the formation of methylandrostane-diol metabolites was observed. Other metabolites resulted from hydroxylation of 17MT at C-6 and C-7 positions and eventual further reduction of the 3-oxo-delta 4 group. They were tentatively assigned the structures of 17 alpha-methyl-4-androsten-6 beta,17 beta-ol-3-one, 17 alpha-methyl-4-androsten-7 xi,17 beta-ol-3-one, and 17 alpha-methyl-5-xi-androstan-3 xi,7 xi-triol. In addition, 17 alpha-methyl-4-androsten-17 beta-ol-3,11-dione and 17 alpha-methyl-17 beta-hydroxy-4,6-androstadiene-3-one were also identified and resulted probably from the oxidation of 11-hydroxy-17MT and dehydration of 6-hydroxy-17MT, respectively.

Mechanism of cadmium-decreased glucuronidation in the rat

In isolated rat hepatocytes, cadmium (0-200 microM) decreased the overall glucuronidation of both isopropyl N-(3-chloro-4 hydroxyphenyl)carbamate (4-hydroxychlorpropham, 4-OHCIPC) and 4-nitrophenol in a concentration-dependent manner. In contrast, in native rat liver microsomes, glucuronidation of 4-OHCIPC was increased by cadmium through activation of microsomal 4-OHCIPC glucuronosyl transferase. In addition, in rat microsome incubations, the net amount of 4-OHCIPC glucuronide was also indirectly increased by cadmium through a reduction in the activity of beta-glucuronidase. As the effect of cadmium on the activity of 4-OHCIPC glucuronosyl transferase could not account for the decrease in glucuronide formation in intact hepatocytes, the influence of cadmium on the availability of UDP-glucuronic acid (UDPGA) was investigated further. In isolated rat hepatocytes, cadmium depleted the UDPGA content in a dose-dependent manner without a change in the UDP glucose (UDPG) content. Cadmium did not increase the breakdown of UDPGA by microsomal UDPGA pyrophosphatase but strongly decreased (30-66%) the synthesis of the cofactor in the cytosol by inhibiting UDP-glucose dehydrogenase (UDPGDH). Cadmium (10-50 microM) was found to inhibit the purified enzyme from bovine liver (EC 1.1.1.22) non-competitively. In vivo in the absence of a substrate undergoing glucuronidation, cadmium administration, 1.5 and 2.5 mg Cd/kg i.v., to normally fed rats resulted in a 15 and 30% decrease of hepatic UDPGA, respectively. However, in the liver, neither the NAD+/NADH ratio nor the UDPG content was significantly changed following cadmium treatment. Both in vitro and in vivo results support the conclusion that in intact cells the reduction in overall 4-OHCIPC glucuronidation caused by cadmium was due to a decrease in UDPGA availability which results from the inhibiting effect of cadmium on UDPGDH.

Use of an immobilized enzyme reactor for the analysis of residues of 17 alpha-methyltestosterone in trout by high-performance liquid chromatography

We have recently observed in trout that 48 h after ingestion of a single dose of [14C]-17 alpha-methyltestosterone ([14C]-MT), 25% of the radioactivity was still in the carcass, corresponding to metabolites of 17-MT. These compounds have no appreciable chromophore, fluorophore or electrophore, therefore the usual detection systems was not satisfactory for their analysis. Consequently a method was developed for high-performance liquid chromatographic separation and detection of two of the major tissue metabolites of 17-MT: 5 alpha-androstane-17 alpha-methyl-3 alpha,17 beta-diol and 5 beta-androstane-17 alpha-methyl-3 alpha,17 beta-diol. A column of immobilized 3 alpha-hydroxysteroid dehydrogenase was prepared and used for detection. The NADH produced from 3-hydroxysteroids by this immobilized enzyme reactor was monitored fluorimetrically. The detection limit of this method, as obtained from the calibration curve, was at the picomole level; the limit of quantification in muscle was 1 microgram/kg, at a signal-to-noise ratio of 4.

Comparative metabolic profiling of chloramphenicol by isolated hepatocytes from rat and trout (Oncorhynchus mykiss)

1. Isolated liver cells from rat and rainbow trout were used to study the biotransformation of labelled chloramphenicol (CP). 2. The 3H-CP metabolic rates were 1.7 nmol/hr/10(6) rat hepatocytes and 0.2 nmol/hr/10(6) trout hepatocytes. 3. In rat, as in trout liver cells, the major metabolite was CP-glucuronide. In addition to this conjugate, CP-base, CP-alcohol and CP-oxamic acid were detected in significant amounts. 4. These results are compared with in vivo data on CP metabolism previously obtained in our laboratory in fish and mammals.

Characterization of xenobiotic metabolizing enzymes in sturgeon (Acipenser baeri)

1. Cytochrome P-450, NADPH-cytochrome c reductase, benzo(a)-pyrene hydroxylase (AHH), 7-ethoxycoumarin-O-deethylase (7-ECOD), epoxide hydrolase (EH), UDP-glucuronyltransferase (UDPGT) and glutathione S-transferase (GSHST) activities in sturgeon (Acipenser baeri) have been measured and partially characterized. 2. Cytochrome P-450-dependent monoxygenase (MO), EH, and conjugation reactions were detected in liver and to a lesser extent in kidney and gills. 3. Hepatic enzyme activities in the sturgeon were equally high or higher than in rainbow trout liver, with the exception of UDPGT whose activity was 14% of that in trout liver. 4. The MO and EH activities displayed the expected pH maxima of 7.5, whereas transferases were relatively independent of the pH in the 6.5-7.5 range. 5. The temperature optima for MO and EH were close to those reported in other fish species, whereas for conjugation reactions the temperature optima were 45 and 60 degrees C for GSHST and UDPGT respectively.

Disposition and metabolism of pristane in rat

The fate of pristane (2,6,10,14-tetramethylpentadecane), a widespread isoprenoid hydrocarbon, has been studied in rats after a single per os administration of 3H-labeled pristane. The balance study showed an extensive fecal excretion (66%) mainly as unchanged hydrocarbon, whereas about 14% of ingested pristane was excreted in urine as pristane metabolites and tritiated water. After one wk, 8.3% of the ingested 3H still was stored in the carcass, and radioactive distribution in tissues and organs showed a preferential incorporation into adipose tissue and liver. Over 75% of the radioactivity stored in the carcass was associated with pristane metabolites and tritiated water. Tissue metabolites were characterized by thin layer chromatography, gas chromatography and mass spectrometric analyses. Four metabolites were identified: pristan-1-ol, pristane-2-ol, pristanic acid and 4,8,12-trimethyltridecanoic acid. These demonstrate that this isoprenoid hydrocarbon undergoes subterminal hydroxylation or terminal oxidation followed by the classical beta-oxidation process. Incorporation of metabolites in phospholipids and more particularly in the phosphatidylserine fraction has been observed and is discussed.

Urinary metabolites of dodecylcyclohexane in Salmo gairdneri: evidence of aromatization and taurine conjugation in trout

1. The urinary metabolites of 3H-dodecylcyclohexane were investigated in rainbow trout, Salmo gairdneri R. after a single intragastric dose. In 72 h, 14% of the ingested radioactivity was excreted in urine. 2. Cyclohexylacetic acid, 1-hydroxy-, 3-hydroxy- and 4-hydroxy-cyclohexylacetic acids were present in the unconjugated fraction. 3. In the glucuronide fraction (1.2% dose) labelled aglycones were cyclohexylacetic acid and phenylacetic acid. 4. More than 30% of the urinary 3H was present as phenylacetic and cyclohexylacetic acids conjugated with taurine.

Disposition and metabolism of chloramphenicol in trout

The urinary and faecal excretion, tissue distribution and metabolism of 3H-chloramphenicol (CP) were measured in rainbow trout, Salmo gairdneri R., after a single 50 mg/kg intragastric dose. The major route of excretion of 3H was faecal (64.3% of the dose), with approx. 16% in the urine in five days. Radioactivity was widely distributed in trout tissues and organs, the highest concen. being in the bile and intestine. At 48 h after dosing, the radioactivity remaining in the liver, the muscle and the perigastric adipose tissue was as CP-derived compounds bound to tissues. In addition to unchanged CP (4.3% dose after 96 h), the other metabolites excreted in the urine were CP base (5.2%), CP alcohol (4.0%) and CP glucuronide (1.8%).