Biotransformation In Rats Research Articles

Structures and conformations of metabolites of antitumor cyclic hexapeptides, RA-VII and RA-X.

Metabolites of antitumor cyclic hexapeptides, RA-VII and -X which were isolated from Rubia cordifolia were studied by hepatic microsomal biotransformation in rats and in bile juice of rabbits to which these drugs were administered intravascularly. Their structures and conformations were elucidated by two-dimensional nuclear magnetic resonance techniques, temperature effect on NH protons and nuclear Overhauser effect experiments. Specific N-demethylation of Tyr-3, O-demethylation and hydroxylation at aromatic rings of Tyr-3 and -5 were observed. Compared with metabolites of RA-VII, most of RA-X was excreted unchanged in the bile juice. Relationship among their structures, conformations and antitumor activities is also discussed.

Effect of ofurace, oxadixyl, and alachlor on xenobiotic biotransformation in the rat liver.

Ofurace, oxadixyl, and alachlor were studied for their effect on hepatic xenobiotic biotransformation in male rats by dosing i.p. with 1 or 100 mg/kg of chemical for 7 days. Ofurace decreased ethoxyresorufin-O-deethylase and aniline p-hydroxylase activities but induced ethoxycoumarin-O-deethylase activity. Glutathione S-transferase and aminopyrine N-demethylase activities responded in a non dose-dependent manner, while cytochrome P-450 content and aldrin epoxidase activities were unchanged. Oxadixyl induced P-450 content, and ethoxycoumarin-O-deethylase and aminopyrine N-demethylase activities. It left ethoxyresorufin-O-deethylase, aldrin epoxidase and epoxide hydrolase activities unchanged and decreased aniline p-hydroxylase activities. Alachlor induced all activities excepting aldrin epoxidase (no change) and aniline p-hydroxylase (decreased). The data indicate that each of these acylanilide pesticides interacts with the monooxygenase system but with differing patterns.

The effect of dietary protein levels on xenobiotic biotransformations in F344 male rats

Diets containing protein levels of 8, 12, and 22% were fed for 14 days to Fischer 344 male weanling rate. Enzyme activities in liver and kidney were measured using several substrates for each of the following enzyme systems: Cytochrome P-450-dependent monooxygenase, ester hydrolysis, and conjugations with sulfate, glutathione, and glucuronic acid. Enzyme activities, for the various mechanisms, decreased from 15 to 65% with decreased dietary protein, with the exception of glucuronide and sulfate conjugation, which increased with decreased dietary protein. In vivo effects were evaluated by measuring hexobarbital sleeping time, procaine paralysis time, and bromcbenzene hepatotoxicity. Increased dietary protein shortened hexobarbital sleeping time and procaine paralysis time, and increased procaine lethality, whereas low protein intake protected against bromobenzene hepatotoxicity. These data suggest that typical laboratory diets (22–25% protein) may provide artificially altered activities of xenobiotic biotransformation in rats, relative to nutritionally adequate (12% protein) diets.

The α2-adrenoceptor antagonist activity of ipsapirone and gepirone is mediated by their common metabolite 1-(2-pyrimidinyl)-piperazine (PmP)

Ipsapirone and gepirone, analogs of buspirone, a newly developed antianxiety agent, form 1-(2-pyrimidinyl)-piperazine (PmP) during their biotransformation in rats. After oral administration (10 mg/kg) of a parent drug, e.g. ipsapirone or gepirone, the metabolite appears in significant amounts in plasma, with maximal concentrations of 0.9 and 1.4 nmol/ml respectively. The metabolite half-life ranges from about 140 to 200 min. Ipsapirone is eliminated more slowly than gepirone, with a half-life of about 100 and 30 min, respectively. The metabolite to parent drug ratios for the areas under the plasma concentration-time curve (AUC) were 1 for ipsapirone and 14 for gepirone. PmP (0.5–2 mg/kg p.o.), ipsapironte gepirone and buspirone (5–20 mg/kg p.o.) dose dependently antagonized the slowing of gastrointestinal transit induced by clonidine 0.1 mg/kg s.c. The doses inhibiting the antitransit effect of clonidine by 50% were 0.8 mg/kg for PmP, 14 mg/kg for ipsapirone and 9 mg/kg for both gepirone and buspirone. Analysis of small intestinal longitudinal muscle of rats given the ED 50 of PmP, ipsapirone, gepirone, buspirone showed that PmP concentrations in the longitudinal muscle (with attached myenteric plexus) fell within a relatively narrow range and were consistent with the appropriate transit scores. The plasma was also tested for anticlonidine activity. These data indicate that PmP formation is a pharmacologically significant metabolic process for the buspirone-related drugs, ipsapirone and gepirone, and that this metabolite is responsible for the α 2-adrenoceptor blocking activity exerted by these drugs in vivo in the rat.

The effect of long-term streptozotocin-induced diabetes on the hepatotoxicity of bromobenzene and carbon tetrachloride and hepatic biotransformation in rats

To exclude the possibility that changes in hepatotoxicity and biotransformation were induced by diabetogen administration, the influence of long-lasting experimental insulin-dependent diabetes on the activities of benzphetamine demethylase, styrene oxide hydrolase, and UDP-glucuronosyl-transferases toward 1-naphthol, diethylstilbestrol, estrone and testosterone, and glutathione S-transferases toward 1-chloro-2,4-dinitrobenzene, ethacrynic acid, and sulfobromophthalein was studied. Adult male Sprague-Dawley rats injected with 45 mg streptozotocin/kg rapidly developed the classical symptoms of diabetes which persisted throughout the 90-day test period. Ketonemia was detectable at 6 but not at either 35 or 90 days after streptozotocin administration. After acute challenge with bromobenzene or carbon tetrachloride (CCl 4), aspartate and alanine aminotransferase activities in rats diabetic for 35 and 90 days were markedly higher than those in normal rats, suggesting that diabetes potentiated the hepatotoxicity of these chemicals. Administration of 25 μl CCl 4/kg, ip, to diabetic rats decreased enzyme activities toward benzphetamine, sulfobromophthalein, 1-chloro-2,4-dinitrobenzene, and 1-naphthol. In normal rats, a dose of 400 μl CCl 4/kg, ip, was required to cause similar changes in enzyme activities. Bromobenzene (500 μl/kg, ip) elicited opposing responses in diabetic and normal rats in N-demethylase activity, in UDP-glucuronosyltransferase activity toward 1-naphthol, estrone, and testosterone, and in glutathione S-transferase activity toward 1-chloro-2,4-dinitrobenzene. Total cytochrome P 450 concentrations were reduced by both induction of diabetes and hepatotoxicant challenge. Thus, chronic uncontrolled diabetes alters the response of hepatic xenobiotic biotransformation enzymes in a non-uniform, substrate-dependent manner, independent of initial diabetogen effects. The role of cytochrome P 450j in potentiating CCl 4 toxicity is discussed.

1-(2-Pyrimidinyl)-Piperazine as Active Metabolite of Buspirone in Man and Rat

Buspirone (BP), a newly developed antianxiety agent, forms 1-(2-pyrimidinyl)-piperazine (PmP) during its biotransformation in rats and man. After oral administration of pharmacologically effective doses of BP-hydrochloride to rats (1 and 10 mg/kg), the metabolite appears in significant amounts in body fluids and tissues; it is highly concentrated in the central nervous system, the brain-to-plasma concentration ratios being approximately 5 at the time of the maximum concentrations (Cmax). In man given the anxiolytic dose (20 mg) of BP the metabolite reaches higher plasma Cmax values than its parent drug. Its plasma elimination t1/2 is more than double that for BP. These results, together with the fact that PmP is biochemically and pharmacologically active, suggest that the metabolite may contribute significantly to the central effects of the parent drug.

Species differences in response to trichloroethylene: II. Biotransformation in rats and mice

Detailed analysis of urine from two strains of rats and mice dosed po with trichloroethylene at four dose from 10 to 2000 mg/kg failed to detect any major species or strain differences in the metabolism of trichloroethylene. Although a greater proportion of the dose was metabolized in mice than in rats, the relative proportions of the major metabolites were very similar in both strains and were unaffected by the dose amount. Analysis of the same urine samples for minor metabolites failed to establish a major species difference. Small amounts of dichloroacetic acid (<1% of the dose) were present in both rat and mouse urine and were not considered significant. Monochloroacetic acid accounted for <0.1% of the dose. Daily dosing of trichloroethylene (1000 mg/kg po) for 180 days did not induce the overall metabolism of trichloroethylene but did double the urinary excretion of trichloroacetic acid. This finding was accompanied by an equivalent percentage decrease in the concentration of trichloroethanol. CO 2 has been shown to be a major metabolite of trichloroacetic acid, suggesting that this is the source of trichloroethylene-derived CO 2. Trichloroacetic acid was also excreted in bile in both rats and mice suggesting possible conjugation of this metabolite in the liver. Very little evidence was found for the formation of chemically reactive species from trichloroethylene in either rats or mice and none that could be the basis of a major species difference. The increased rate of metabolism in the mouse, the resulting high blood concentrations of trichloroacetic acid, and stimulation of hepatic peroxisome proliferation in this species appears to be the major species difference possibly related to tumor formation in the liver. The conjugation of trichloroacetic acid and its metabolism to CO 2 may be related to peroxisome proliferation.

2-14C-1-(2′-deoxy-β-d-ribofuranosyl)-5-ethyluracil: Synthesis and biotransformation in rats

With 14C-urea as the starting material, 2-14C-1-(2′-deoxy-β-D-ribofuranosyl)-5-ethyluracil [2-14C-β-5-ethyl-2′-deoxyuridine] was synthesized for metabolic studies. After intravenous administration in rate, the radioactivity disappeared in the blood within 72 hr, being eliminated primarily in the urine (97%). The major elimination took place in the first 24hr (92%). Little radioactivity was detected in the organs and tissues after 3days. Approximately 50% of the urine radioactivity probably was due to an unidentified conjugate, 30% was due to Metabolite II, and 20% was unchanged drug. Metabolite II was identified as 5-ethyluracil by mass and 1H-NMR spectra and by comparison with an authentic sample.

Modification of microsomal membrane components and induction of hepatic drug biotransformation in rats on a high cholesterol diet.

Abstract The effect of cholesterol on the microsomal membrane components and the induction of drug–metabolizing enzymes was studied in rats after feeding with a two per cent cholesterol diet and administration of phenobarbitone or 3–methylcholanthrene intraperitoneally. The results revealed that cholesterol affected both the amount and the binding properties of protein, phospholipid and cholesterol in microsomes. Cholesterol also modified the effects of phenobarbitone and 3–methylcholanthrene on microsomal membranes. The administration of inducers increased the liver–body weight ratio significantly. Phenobarbitone enhanced NADPH cytochrome c reductase activity in native microsomes by about 2–fold. The aryl hydrocarbon hydroxylase activity was increased markedly by both phenobarbitone and 3–methylcholanthrene. The UDPglucuronosyltrans–ferase activity was also enhanced by both inducers. After trypsin digestion of microsomes UDPglucuronosyltransferase activity was significantly higher in rats on a high cholesterol diet than in those on standard diet. After treating the microsomes in vitro by various membrane perturbants it was found that 3–methylcholanthrene made the enzyme proteins less soluble than phenobarbitone. The results support the idea that cholesterol affects the activities of drug metabolizing enzymes, due to changes in the structure of microsomal membranes.

2966. Acrylonitrile metabolism: Gut, I., Nerudová, J., Kopecký, J. & Holecěk, V. (1975). Acrylonitrile biotransformation in rats, mice, and Chinese hamsters as influenced by the route of administration and by phenobarbital, SKF 525-A, cysteine, dimercaprol, or thiosulfate. Arch. Tox.33, 151

2966. Acrylonitrile metabolism: Gut, I., Nerudová, J., Kopecký, J. & Holecěk, V. (1975). Acrylonitrile biotransformation in rats, mice, and Chinese hamsters as influenced by the route of administration and by phenobarbital, SKF 525-A, cysteine, dimercaprol, or thiosulfate. Arch. Tox.33, 151

Acrylonitrile biotransformation in rats, mice, and chinese hamsters as influenced by the route of administration and by phenobarbital, SKF 525-A, cysteine, dimercaprol, or thiosulfate

Female wistar rats, conventional albino mice, and Chinese hamsters were given a single dose of acrylonitrile, 0.5 or 0.75 mM/kg body weight. The elimination in the urine of thiocyanate, which is the main metabolite of acrylonitrile, indicated a decreasing proportion of biotransformation after oral (over 20%), intraperitoneal, or subcutaneous (2 to 5%), and intravenous (1%) administration in rats. Oral administration of acrylonitrile in hamsters and mice was also followed by higher biotransformation than intraperitoneal administration. Pretreatment of rats with phenobarbital, SKF 525 A, cysteine, or dimercaprol did not significantly influence elimination of thiocyanate in the urine after the administration of acrylonitrile, but simultaneous administration of thiosulfate significantly increased the metabolized portion of acrylonitrile given intraperitoneally in rats (almost twice) and mice (more than three times). Acrylonitrile was found to be strongly bound in blood. The study confirmed the marked effect of distribution (first-pass metabolic phenomenon) on the metabolic fate of foreign compounds. The strong acrylonitrile binding and cyanoethylation are apparently responsible for the unusually high influence of the different routes of administration on the metabolic fate of acrylonitrile. Acrylonitrile was more effectively metabolized to thiocyanate in mice than in rats after oral, intraperitoneal, and intravenous administration. A greater response of acrylonitrile to thiocyanate metabolism and a larger decrease in its acute toxicity after thiosulfate in mice than in rats indicate possible differences in the mechanism of acrylonitrile toxicity in these animals. Cyanide apparently plays a minor role in the acrylonitrile toxicity in rats, but may play quite an important one in mice.

Comparative effects of adenosine and adenine and guanine nucleotides on drug biotransformation in rats

The effect of various nucleotides and adenosine on the hepatic biotransformation of hexobarbital sodium (HB) and p-chloro-N-methylaniline (PCMA) was determined in male rats. Intraperitoneal administration of dibutyryl cyclic adenosine 3',5'-monophosphate (DBcAMP), alone and in combination with theophylline, and the cyclic adenosine 3',5'-monophosphate (cAMP)-theophylline combination prolonged HB sleeping time by more than 70%. cAMP or dibutyryl cyclic guanosine 3',5'-monophosphate (DBcGMP), alone or in combination with theophylline, failed to significantly alter the duration of HB-induced hypnosis. Plasma levels of HB upon awakening suggested that the increase in sleeping time was apparently not due to an altered sensitivity of the brain to the barbiturate. The effect appears to be related to an impairment of HB metabolism since only those compounds that inhibited HB oxidation when added to liver slices prolonged hypnosis. In addition, 5'-AMP, adenosine, and cyclic guanosine 3',5'-monophosphate (cGMP) failed to alter HB biotransformation by liver slices. A similar pattern of impairment of metabolism by liver slices was observed when PCMA was used as the substrate. The inhibitory effect of DBcAMP was not altered by concurrent addition of either cGMP or DBcGMP. No impairment in the rate of microsomal PCMA biotransformation resulted from addition of adenosine or any of the nucleotides used in this study.

Metabolism of cloxazolam I. Distribution, excretion and biotransformation in rats and mice.

The distribution, excretion and biotransformation of 14C-cloxazolam were studied in rats and mice. The tissue concentration reached the maximum at about 1 and 3 hr after oral administration to rats and mice, respectively. The brain concentration was higher and lasted longer in mice than in rats. In the whole-body autoradiograms of mice, no significant radioactivity was detected in the tissues except the liver after 24 hr and the radioactivity disappeared almost completely after 72 hr. The recovery of radioactivity was considerably higher in the feces than in the urine and was about the same regardless of the route of administration in both rats and mice. In the in situ cannulated rats, the most of the oral dose was recovered in the bile in 24 hr period. Eighteen radioactive metabolites were detected in the liver, urine and feces after oral administration of 14C-cloxazolam. Among them, eight metabolites including 7-chloro-2, 3-dihydro-5-[o-chlorophenyl]-2H-1, 4-benzodiazepin-2-one, 7-chloro-5-[o-chlorophenyl]-1, 3-dihydro-3-hydroxy-2H-1, 4-benzodiazepin-2-one (COX) and 2-amino-3-hydroxy-2', 5-dichlorobenzophenone (ADCB-OH) were isolated and identified. The main metabolites in the mouse urine were the glucuronides of COX and ADCB-OH, while in the rat urine two unidentified metabolites in addition to the above two. In the mouse feces, COX and ADCB-OH and their conjugates were the main metabolites, while in the rat feces a much larger number of metabolites were detected.