Search

Introduction: To determine, via narrative, non-systematic review of pre-clinical and clinical studies, whether the effect of cannabis on hepatic biotransformation pathways would be predicted to res...

We have investigated the in vitro metabolism of pectenotoxin-2 (PTX-2) using primary hepatocytes from Wistar rats in suspension. Purified PTX-2 was rapidly metabolized. Two major and several minor oxidized PTX-2 metabolites were formed, none of which had retention times corresponding to PTX-1, -11, or −13. Hydrolysis products, such as PTX-2 seco acid, were not observed. Preliminary multi-stage LC-MS analyses indicated that the major hepatic PTX-2 metabolites resulted from the insertion of an oxygen atom at the positions C-19 to C-24, or at C-44. The rapid oxidative metabolism may explain the low oral toxicity of PTXs observed in vivo studies., Highlights • PTX-2 is rapidly metabolized in rat hepatocytes. • Two major and several minor oxidized PTX-2 metabolites were formed. • The results may explain the low oral toxicity of PTXs observed in vivo studies.

Cytochrome P450 enzymes (CYP) are important catalyzing proteins involved in the biotransformation of endogenous and xenobiotic compounds. However, their expression and/or activity can be altered by exposure to contaminants such as mycotoxins. In vitro incubations in porcine hepatic microsomes revealed a potent inhibition of the midazolam (CYP3A) biotransformation by T-2 toxin (T-2) (Ki = 27.0 +/- 3.97 mu M) and zearalenone (ZEA) (Ki = 1.1 +/- 0.22 mu M). Consequently, the in vivo impact of 2 weeks exposure to T-2 (1,000 mu g/kg feed) or ZEA (500 mu g/kg feed) on the pharmacokinetics (PK) of midazolam (MDZ) as a CYP3A probe drug was investigated in pigs, and was compared to a control group receiving no mycotoxins. MDZ was chosen as this drug undergoes substantial first-pass metabolism in humans with equal contribution of the intestine and liver. Each pig received a single intravenous (0.036 mg/kg BW) and oral (0.15 mg/kg BW) dose of midazolam (MDZ). For the IV bolus no differences were observed in PK between control and mycotoxins exposed groups. However, oral plasma concentration-time profiles showed quantitative differences in absolute oral bioavailability F[p-value (ANOVA) = 0.022], AUC_0-inf (mu g*h/L) [p-value (ANOVA) = 0.023], Ke (1/h) [p-value (ANOVA) = 0.004], and Ka (1/h) [p-value (ANOVA) = 0.031]. Although only differences in Ke estimates after oral administration reached significance in the post hoc analysis due to inequality of the variances. We hypothesize that the observed trends after ZEA and T-2 exposure are related to the cytotoxic effect of T-2, resulting in an increased absorption rate constant Ka. For ZEA, an inhibition of the CYP3A enzymes is suggested based on the in vitro inhibition potential and increase in oral bioavailability. Further research is required to confirm the current hypothesis.

Flubendazole (FLBZ) is a broad-spectrum benzimidazole anthelmintic used in pigs, poultry, and humans. It has been proposed as a candidate for development for use in elimination programmes for lymphatic filariasis and onchocerciasis in humans. Moreover, FLBZ has shown promise in cancer chemotherapy, particularly for neuroblastoma. This work investigated the hepatic carbonyl-reducing pathway of FLBZ in different species, including humans. Microsomal and cytosolic fractions were obtained from sheep, cattle, pig, hen, rat, and human liver. Both subcellular fractions of each species converted FLBZ into a reduced metabolite (red-FLBZ). The rate of microsomal red-FLBZ production was highest in sheep (1.92 ± 0.13 nmol/min.mg) and lowest in pigs (0.04 ± 0.02 nmol/min.mg); cytosolic red-FLBZ production ranged from 0.02 ± 0.01 (pig) to 1.86 ± 0.61 nmol/min.mg (sheep). Only subcellular fractions from sheep liver oxidized red-FLBZ to FLBZ in a NADP+-dependent oxidative reaction. Liver microsomes from both pigs and humans transformed FLBZ to red-FLBZ and a hydrolyzed metabolite. Very significant differences in the pattern of FLBZ metabolism were observed among the tested species and humans. These results reinforce the need for caution in extrapolating data on metabolism, efficacy, and safety of drugs derived from studies performed in different species. Fil: Maté, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigación Veterinaria de Tandil. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigación Veterinaria de Tandil. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Centro de Investigación Veterinaria de Tandil; Argentina Fil: Geary, T.. McGill University; Canadá Fil: Mackenzie, C.. Michigan State University; Estados Unidos Fil: Lanusse, Carlos Edmundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigación Veterinaria de Tandil. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigación Veterinaria de Tandil. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Centro de Investigación Veterinaria de Tandil; Argentina Fil: Virkel, Guillermo Leon. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigación Veterinaria de Tandil. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigación Veterinaria de Tandil. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Centro de Investigación Veterinaria de Tandil; Argentina

Selenium (Se) is an essential nutrient that has a relatively narrow window between ingested amounts that result in deficiencies and those that cause toxicoses. Historically, occurrences of livestock disease that is suggestive of chronic selenium poisoning were recorded in the 13th century. Marco Polo wrote of such cases in western China in 1295. Selenium deficiency, acute poisoning, and chronic selenosis are still commonly encountered. Since first identified as an essential nutrient, selenium has been found to act in several key enzymatic systems and plays several roles in normal immune function, reproductive function, hepatic biotransformation reactions, neurotransmitter turnover, and anticarcinogenic functions.

Zearalenone (ZEA) as mycoestrogen is found in human foods and animal feeds. Its estrogenic potency depends on its biotransformation fate. The hepatic biotransformation of ZEA in two species of sturgeon fish (Acipenser persicus and Huso huso) was investigated. ZEA was incubated with the hepatic microsomal and post-mitochondrial sub-fractions in the presence of NADPH and the metabolites were determined by means of HPLC. Moreover, the rate of glucuronidation for ZEA and its metabolites were estimated in the presence of uridine diphosphateglucuronic acid. β-zearalenol (β-ZOL) was found to be the major metabolite of ZEA by both sub-fractions. Enzymatic kinetics studies revealed that the maximum velocity (Vmax) in microsomal and post-mitochondrial fractions for β-ZOL production was found 5- and 7-folds in Huso huso and 8- and 12-folds in A. persicus higher than that for α-ZOL production, respectively. The H. huso hepatic post-mitochondrial fraction mainly glucurinated ZEA while in A. persicus, the metabolites and in particular β-ZOL were glucuronidated. Data suggest that the hepatic biotransformation of ZEA in studied sturgeons resulted in detoxification of ZEA as the main metabolite tends to be β-ZOL with weaker estrogenic property. Moreover, clear differences in glucuronidation profile are indicating interspecies variety in hepatic biotransformation of ZEA.

Scientists studying mammals have developed a stepwise approach to predict in vivo hepatic clearance from measurements of in vitro hepatic biotransformation. The resulting clearance estimates have been used to screen drug candidates, investigate idiosyncratic drug responses, and support chemical risk assessments. In this report, we review these methods, discuss their potential application to studies with fish, and describe how extrapolated values could be incorporated into well-known compartmental kinetic models. Empirical equations that relate extrapolation factors to chemical log Kow are given to facilitate the incorporation of metabolism data into bioconcentration and bioaccumulation models. Because they explicitly incorporate the concept of clearance, compartmental clearance-volume models are particularly well suited for incorporating hepatic clearance estimates. The manner in which these clearance values are incorporated into a given model depends, however, on the measurement frame of reference. Procedures for the incorporation of in vitro biotransformation data into physiologically based toxicokinetic (PBTK) models are also described. Unlike most compartmental models, PBTK models are developed to describe the effects of metabolism in the tissue where it occurs. In addition, PBTK models are well suited to modeling metabolism in more than one tissue.

The hepatic biotransformation of aldrin (AD) and dieldrin (DD) was studied in liver post-mitochondrial supernatants (S-9s) from laying hens, female cattle and swine. S-9s were incubated with 0.03 nmol o f AD or DD for 1 h. After 1 h, AD in the samples was almost epoxidated to DD. This formation was found with all the animal S-9s, and the highest rates occurred in pig S-9 (P < 0.01), followed by cow and hen S-9s. No reduction of DD was found with any of the S-9s.

We report changes in biomarker enzymes (cytochrome P4501A, glutathione-S-transferase) and protein expression (cytochrome P4501A) in adult painted turtles, Chrysemys picta, as part of a study of the potential impact of contaminants originating from the Massachusetts Military Reservation on Cape, Cod, MA. In animals from both Moody Pond, a site potentially impacted by contaminants, and Washburn Pond, a nonimpacted site, rates of hepatic microsomal ethoxyresorufin-O.

The influences of the gestational age (range: 28-36 weeks) and the postnatal age (range: 6–100 days) on the biotransformation capacity of the liver were studied in 51 preterm appropriate-for-gestational-age infants and in 20 preterm small-for-gestational-age infants using the [15N]methacetin urine test. Methacetin is a test drug assessing a two-step pathway of biotransformation including monooxygenation and conjugation. After oral administration of 3 mg [15N]methacetin/kg body-weight, the cumulative 15N excretion in urine during the consecutive 9 h was measured and used as a marker of microsomal biotransformation capacity. In preterm appropriate-for-gestational-age infants, the biotransformation capacity increases with gestational age as well as with postnatal age, but the strongest correlation could be found between cumulative [15N] excretion and postmenstrual age. Intrauterine growth retardation results in lower biotransformation capacity (26.3 ± 11.3 vs. 36.1 ± 9.6% [15N] excretion, expressed as percentage of intake) and disturbed postnatal development of this hepatic function. The data indicate that normal intrauterine development is a prerequisite for normal postnatal development of the biotransformation capacity, which might have consequences for the metabolism and efficacy of certain drugs in small-for-gestational-age infants.

The xenobiotic-metabolizing enzyme system of hatchery golden ide [Leuciscus idus (L.)] were tested for applicability in biological monitoring in rivers. The golden ide, cyprinid fish used for toxicity testing, were caged for 1 to 3 weeks in flowthrough systems at various locations of the river Elbe. The activities of 7-ethoxycoumarin-O-deethylase (ECOD) and the cytochrome P450 (P450) concentrations in the livers were analyzed. Exposure in the river Elbe increased the ECOD activity and the P450 concentration. In a flowthrough basin located in the harbor of Hamburg the ECOD activity increased up to 3.5 times, and the P450 concentration increased slightly by a factor of 1.5. During exposure of the golden ide at two Elbe stations upstream and downstream the city of Hamburg, levels of P450 in the livers did not change significantly when compared with laboratory controls. There was, however, a significant increase of ECOD activity between stations Bunthaus (upstream) and Blankenese (downstream). The ECOD activity in the livers of golden ide caged downstream were significantly higher compared to those at the upstream station. The results presented in this study suggest that golden ide can be employed as experimentals for routine measurements in limnic habitats using biochemical assays.

Previous studies have reported that fentanyl is eliminated predominantly by hepatic biotransformation, and that some is eliminated unchanged in urine and stools. No reports have described the elimination of fentanyl via the lungs. In this study, exhaled gas samples from eight anaesthetized patients undergoing cardiac surgery were analysed using solidphase microextraction (SPME) coupled with gas chromatography–mass spectrometry (GC–MS). Results confirmed that fentanyl was exhaled by patients after intravenous administration, that the concentration of exhaled fentanyl fluctuated with time and peak concentrations were reached approximately 15-20 min after intravenous fentanyl administration. Thus, in addition to hepatic biotrans formation and elimination via urine and faeces, fentanyl is also eliminated unchanged by the lungs. The potential risk to operating theatre personnel from long-term exposure to low levels of exhaled anaesthetic agents following intravenous administration to patients during surgery warrants further research.

Resume Chez l'homme, l'administration intraveineuse de 2 g de piperacilline a 6 sujets normaux a donne lieu a un passage moyen de 0,08 ± 0,03 % dans le liquide d'aspiration duodenale recueilli pendant les 4 heures succedant a l'injection. Chez 10 patients cholecystectomises porteurs d'un drain de Kehr, cette elimination biliaire (0–24 h) s'est elevee a 0,65 ± 0,17 % de la dose (2 g IV) et la clairance biliaire a 0,80 ml/min. ; un pic biliaire de 211 ± 64 μg/ml a ete observe a la deuxieme heure. Les concentrations de piperacilline mesurees dans la bile choledocienne, la bile vesiculaire et des fragments de paroi vesiculaire preleves simultanement, de maniere per-operatoire en cours de cholecystectomie chez 10 patients, 1 heure apres injection de l'antibiotique (2 g IV) atteignaient respectivement 382 ± 110, 30,8 ± 20,5 μg/ml et 10,5 ± 2,6 μg/g. Tous les dosages ont ete realises par une technique HPLC. Les caracteristiques pharmacocinetiques biliaires de la piperacilline ont ete comparees a celles de 20 autres beta-lactamines precedemment etudiees selon la meme procedure. Les resultats du present travail s'inscrivent en faveur de l'utilisation de la piperacilline dans le traitement des infections du tractus biliaire. Dans un cas (drain de Kehr), la pratique simultanee de dosages microbiologiques et chromatographiques a mis en evidence des taux similaires dans le serum, mais des concentrations “microbiologiques” nettement plus elevees que les taux HPLC dans la bile et les urines, traduisant la presence vraisemblable de metabolites actifs de la piperacilline dans ces deux liquides biologiques.

Hydroxylation and acetylation of sulphamonomethoxine (SMM) and deacetylation of N4-acetyl SMM (N4-AcSMM) were estimated in liver post-mitochondrial supernatants (S-9) from laying hens, female cattle, swine and rats. The formation of hydroxylated SMM, 2,6-dihydroxy SMM (2,6-diOH-SMM), was found only with hen S-9s. N4-acetylation rate of SMM was the highest in pig S-9s, followed by rat, then hen or cow S-9s. All S-9s from the four species deacetylated N4-AcSMM. In hen S-9s, the rate of 2,6-dihydroxylation was higher during incubation at 41 °C than at 37 °C.

8533 Background: CY is an inactive pro-drug that requires hepatic biotransformation into its primary cytotoxic metabolite, 4-hydroxycyclophosphamide (HCY). The fractionated CY (FCY) schedule described is clinically relevant with a reported 59% response rate in advanced or refractory solid tumors. Because of proposed CY metabolic auto-induction it was hypothesized that the sum of the areas-under-the-curve (AUCs) of HCY for the FCY schedule would exceed the AUC of the standard (SCY) schedule, and that the sum of the 24-hour urinary CY recovery would be less with FCY than SCY. Methods: Patients received FCY x 1 [CY 500 mg/m2/day x 5 days plus etoposide 100 mg/m2/day x 5 days] and SCY x 1 [CY 2.5 g/m2/day x 1 plus etoposide 100 mg/m2/day x 5 days], each given 3 weeks apart. Patients were randomized to receive FCY as the first or second course. Courses were followed by G-CSF (5 micorgrams/kg/day). Serum samples drawn at hours 0, 0.5, 1, 3, 6, 8 and 24 after CY administration, were analyzed for HCY by HPLC with...

Dehydrocholic acid was administered intravenously to a patient and to rats, and its metabolites excreted into bile were studied by gas chromatography-mass spectrometry as ethyl ester-dimethylethylsilyl ether-methyloxime derivatives. Two 7β-hydroxy metabolites were identified : 3α, 7β-dihydroxy-12-oxo-5β-cholanoic acid in both human and rat bile, and 3α, 7β, 12α-trihydroxy-5β-cholanoic acid in rat bile. This indicates that human and rat livers are able to reduce the 7-oxo group in dehydrocholic acid to both 7α-and 7β-hydroxy forms.

The present preliminary report on studies of the influence of pulp bleach plant effluents on hepatic biotransformation enzymes in fish is a part of a major characterisation of biochemical and physiological effects of effluents from pulp industries in Sweden. Our studies on the xenobiotic biotransformation enzymes demonstrate, so far, that the pulp effluents have the potential to strongly induce 7-ethoxyresorufin-O-deethylase activity (EROD) in fish liver and that fish living in the receiving water of an effluent from a pulp bleach plant have induced hepatic EROD activities as well as higher hepatic UDP glucuronyltransferase activities than those living in an unpolluted area. It is thus apparent that measures of induction of biotransformation enzymes in fish liver may be a useful approach in monitoring the presence of potential hazardous compounds released from pulp industries.

Resume L'elimination biliaire et la disponibilite hepatique d'une beta-lactamine, la ticarcilline et d'un inhibiteur de beta-lactamases, l'acide clavulanique ont ete etudiees au moyen de 5 perfusions de foie isole de lapin. Les concentrations biliaires de ticarcilline demeurent inferieures aux taux seriques pendant toute la duree de la perfusion et l'elimination cumulee sur 3 heures represente 1,3 ± 0,2 % de la dose administree. La teneur hepatique en ticarcilline a la fin de la perfusion est nulle. Les concentrations et l'elimination biliaire de l'acide clavulanique (0,4 ± 0,1 %) sont plus faibles encore. Dans les conditions de l'experience, la stabilite de l'acide clavulanique s'avere moindre que celle de la ticarcilline du fait d'une plus grande biotransformation hepatique (31,4 % vs 26,4 %). Une validation de ces resultats par des etudes cliniques effectuees chez l'homme serait necessaire avant d'envisager favorablement l'utilisation de cet antibiotique dans le traitement des infections du tractus biliaire.

1. 1. In liver microsomes of juvenile (1 + year old) rainbow trout the monooxygenase activities were higher in April (water temp 3°C) than in June (water temp 16°C), which indicates that the monooxygenase complex shows a partial compensatory response to temperature changes. 2. 2. UDP-glucuronosyltransferase followed compensatory changes similar to the monooxygenase complex. 3. 3. The Q 10 -values for 7-ethoxycoumarin- O -deethylase varied from 2 to 2.5 at saturated substrate concentration between the temperature range of 5–20°C. The Q 10 -value diminished significantly at higher assay temperatures.

N-demethylation of aminopyrine and C-hydroxylation of aniline by hepatic microsomal enzymes were measured during in vitro exposure to cigarette smoke. Metabolism of aminopyrine during smoke exposure was not significantly altered. Metabolism of aniline during smoke exposure was inhibited 70–80% (P < .001) thus indicating that an initial effect of exposure to cigarette smoke is a decreased rate of biotransformation via C-hydroxylation. This finding, coupled with the findings of other investigators who have shown that the delayed effect of exposure to cigarette smoke is induction of hydroxylase activity, suggests that cigarette smoke produces a biphasic alteration in certain hepatic biotransformation processes.

1. 1. Seasonal and sex variations in the cytochrome P 450 content and monooxygenase and glucuronidation activities were observed in the liver microsomes of rainbow trout cultivated in North-European waters. 2. 2. During the summer the specific monooxygenase activities lowered but the total calculated capacity remained unchanged (measured at 18°C) or increased (measured at environmental temperatures) due to liver growth. 3. 3. During water cooling in autumn the specific monooxygenase activity as well as the total capacity showed an ideal temperature compensation and remained unchanged if measured at environmental temperatures but increased considerably if measured at 18°C. 4. 4. Before the spawning time cytochrome P 450 and the monooxygenase activities lowered in both sexes but more in females revealing a temporary sex difference which disappeared after spawning. 5. 5. The specific UDP glucuronosyltransferase activity lowered considerably during the cooling of environmental temperature, and thereafter an increase in both sexes was observed towards the spawning time (significantly higher in females) and coming summer.

A “tissue culture” method for testing the cytotoxic activity of compounds active through the formation of metabolites is described and cyclophosphamide (CPA), which is known to exert its effect only after hepatic biotransformation, has been chosen as “model” substance. A monolayer of cultured KB cells is treated for one hour with CPA at 37°C, in the presence of different amounts of microsomal enzymes (105,000 × g fraction) and their co-factors and at the end of the incubation the medium is removed and changed. A dose-effect relation is observed by measuring the inhibition of growth or the destruction of the KB cells after 24 hr. The significance of this procedure for screening purposes or for studying the possible cytotoxicity of unstable metabolites is outlined.

Single-pass perfusion in situ of mouse livers with the organophosphate paraoxon resulted in formation of p -nitrophenol (PNP), p -nitrophenyl sulfate (PNPS), and p -nitrophenyl-β-D-glucuronide (PNPG). Following initiation of perfusion of paraoxon steady—state conditions were achieved in 15–25 min, at which time the extraction ratio was 0.55 (S.D. = 0.05). This suggests the capacity of mouse liver to biotransform paraoxon is not as great as previously reported. At all concentrations of paraoxon examined the amount of PNPS produced exceeded that of PNPG. However, as the concentration of paraoxon increased the relative proportion of PNP to PNPS and PNPG increased, indicating the capacity of liver to biotransform paraoxon exceeded the capacity to biotransform PNP. Single-pass perfusion in situ of mouse livers with PNP resulted in production of PNPS and PNPG. As with paraoxon, steady—state conditions were achieved in 15–25 min. The extraction ratio of PNP, as well as the metabolic profile, changed markedly with varying concentrations of PNP. At PNP reservoir concentrations of 4 μM or less the extraction ratio of PNP was 1, with all PNP metabolized to PNPS. As PNP concentrations increased (up to 75 μM) both unchanged PNP and PNPG appeared in the effluent. Thus the hepatic biotransformation of PNP was clearly dependent on substrate concentration.

Tricyclic antidepressants have been well characterized in terms of their pharmacokinetics. They are typical “high-clearance” drugs with elimination largely (> 97%) by hepatic biotransformation, high systemic clearance (0.2–1.2 1/min), and accordingly substantial elimination by first-pass metabolism.1 The metabolism takes place primarily by demethylation, hydroxylation, and glucuronide conjugation.2 Tricyclic antidepressants were among the first classes of drugs for which pronouned interindividual variations in pharmacokinetics, in particular clearance and steady-state levels on fixed doses, were shown.2,3 The clinical consequences of this variability for therapeutic and unintended effects have been reviewed elsewhere.4

Summary Neither destruction of thymus by N-methylnitrosourea or by X-rays nor thymectomy or splenectomy in rats of different ages affected hexobarbital sleeping time, ethylmorphine N-demethylation or ethoxycoumarin O-deethylation significantly and systematically. Thymectomy or thymus destruction by x-rays of newborn rats did not significantly influence postnatal development or inducibility by phenobarbital of the monooxygenase reactions.