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Effect of PCB on some MFO enzyme activities in pregnant and virgin rabbits.

Fenclor 64 (a PCB's commercial mixture) was administered twice i.p. to virgin and pregnant New Zealand rabbits at the dose of 100 mg/Kg to evaluate its inducing properties on the following hepatic microsomal MFO activities: p-nitro-anisole-O-demethylase, amino-pyrine-N-demethylase, acetanilide-hydroxylase and aryl-hydrocarbons-hydroxylase. The results indicate that Fenclor 64 evoked a "mixed type" induction in virgin as well as in pregnant rabbits since it increased liver weight, cytochrome P-450 levels, as well as p-nitro-anisole-O-demethylase and acetanilide-hydroxylase. Pregnancy by itself affects only amino-pyrine-N-demethylase levels.

Aminopyrine N-Demethylase↗

The effect of aniline derivatives on absorption of fluid, glucose and sodium in isolated duodenal segments from rats.

Paracetamol (5-15 mmol X l-1), phenacetin (1-3 mmol X l-1) and acetanilide (5-20 mmol X l-1) enhanced fluid, glucose and sodium absorption of isolated duodenal segments from rats. In a high concentration paracetamol (30 mmol X l-1) and acetanilide (25 mmol X l-1) inhibited these parameters. The coupling coefficient of 2:1 in sodium-glucose cotransport was not changed under the influence of the aniline derivatives. Phlorizin (10(-5) mol X l-1) completely abolished the stimulatory effect of these drugs. Also in presence of 3-O-methylglucose instead of glucose in the perfusion medium a paracetamol dependent increase in fluid absorption was seen, whereas the absorption of mannitol was unchanged. The results suggest, that the increase in sodium and fluid absorption caused by aniline derivatives is due to the stimulation of active glucose transport. A cytotoxic effect may explain the decrease of absorption at high concentrations of these substances.

Aniline Compounds↗

Comparative sensitivity of Selenastrum capricornutum and Lemna minor to sixteen herbicides.

Aquatic plant toxicity tests are frequently conducted in environmental risk assessments to determine the potential impacts of contaminants on primary producers. An examination of published plant toxicity data demonstrates that wide differences in sensitivity can occur across phylogenetic groups of plants. Yet relatively few studies have been conducted with the specific intent to compare the relative sensitivity of various aquatic plant species to contaminants. We compared the relative sensitivity of the algae Selenastrum capricornutum and the floating vascular plant Lemna minor to 16 herbicides (atrazine, metribuzin, simazine, cyanazine, alachlor, metolachlor, chlorsulfuron, metsulfuron, triallate, EPTC, trifluralin, diquat, paraquat, dicamba, bromoxynil, and 2,4-D). The herbicides studied represented nine chemical classes and several modes of action and were chosen to represent major current uses in the United States. Both plant species were generally sensitive to the triazines (atrazine, metribuzin, simazine, and cyanazine), sulfonureas (metsulfuron and chlorsulfuron), pyridines (diquat and paraquat), dinitroaniline (trifluralin), and acetanilide (alachlor and metolachlor) herbicides. Neither plant species was uniformly more sensitive than the other across the broad range of herbicides tested. Lemna was more sensitive to the sulfonureas (metsulfuron and chlorsulfuron) and the pyridines (diquat and paraquat) than Selenastrum. However Selenastrum was more sensitive than Lemna to one of two thiocarbamates (triallate) and one of the triazines (cyanazine). Neither species was sensitive to selective broadleaf herbicides including bromoxynil, EPTC, dicamba, or 2,4-D. Results were not always predictable in spite of obvious differences in herbicide modes of action and plant phylogeny. Major departures in sensitivity ofSelenastrum occurred between chemicals within individual classes of the triazine, acetanilide, and thiocarbamate herbicides. Results indicate that neither species is predictively most sensitive, and that a number of species including a dicot species such as Myriophyllum are needed to perform accurate risk assessments of herbicides.

Chlorophyta↗

Identification of the chloramphenicol-hydrolyzing enzyme of guinea pig liver as one of the nonspecific carboxylesterases.

Guinea pig liver has the highest chloramphenicol-hydrolyzing capacity among the livers of various mammals. The enzyme responsible for the hydrolysis of the amide-bond in chloramphenicol is one of the isoenzymes of the microsomal nonspecific carboxylesterases. This isoenzyme is related to the well-known acetanilide-hydrolyzing carboxylesterases/amidases of pig and rat liver. The guinea pig liver enzyme is purified 24-fold starting with microsomes. The purified enzyme is essentially free from other proteins except other carboxylesterase isoenzymes with similar properties. The chloramphenicol-hydrolyzing esterase has an apparent molecular weight of about 180,000, a subunit weight of 60,000 and a pH optimum at 8.5. It also hydrolyzes methyl butyrate and acetanilide and it is completely inhibited by diethyl-4-nitrophenyl phosphate. Two assay procedures for the enzymatic chloramphenicol hydrolysis are described: a thin-layer chromatographic assay using radioactive chloramphenicol and a colorimetric assay utilizing the reaction of the liberated amine with trinitrobenzenesulfonic acid.

Animals↗

Inducing effect of oxfendazole on cytochrome P450IA2 in rabbit liver. Consequences on cytochrome P450 dependent monooxygenases.

Male New Zealand rabbits were dosed with either 0.9, 4.5 or 22.5 mg/kg/day of oxfendazole by gastric intubation for 10 days. Oxfendazole administered at the therapeutic dose (4.5 mg/kg) and at the highest dose (22.5 mg/kg) increased 1.54- and 2.36-fold the total liver microsomal cytochrome P450 and more particularly the isoenzyme P450IA2 (95 and 184% increases) as demonstrated by western blotting. Increases in ethoxyresorufin O-deethylation and hydroxylations of benzopyrene and acetanilide occurred in livers of the same animals without any change in N-demethylation of aminopyrine, benzphetamine or erythromycin. Because of the unchanged level of mRNA specific to cytochrome P450IA2, as shown by northern blot analysis of poly mRNA, an enzyme stabilization rather than a transcriptional activation of IA2 genes should be involved in the P450IA2 regulation mechanisms. Oxfendazole bound strongly to cytochrome P450, giving rise to a type II spectrum, and inhibited noncompetitively the ethoxyresorufin O-deethylase and acetanilide hydroxylase activities, this confirmed that oxfendazole interacts only with the P450IA2 family. On the basis of a comparison of the enzymatic activities induced by various imidazole drugs, it was concluded that oxfendazole, like omeprazole and albendazole, behaved as a 3-methylcholanthrene-type inducer. These three benzimidazoles did not all belong to the same category of cytochrome P450 inducers as the antifungal drugs miconazole, clotrimazole and ketoconazole.

Animals↗

Developmental and tissue-specific differential regulation of the mouse dioxin-inducible P1-450 and P3-450 genes.

The murine Ah locus has two structural genes, P1-450 and P3-450, that are members of the 2,3,7,8-tetrachlorodibenzo-p-dioxin-inducible P-450 gene family and are closely linked on mouse chromosomes 9. Transcriptional activation of both genes in liver is controlled by the Ah receptor. Inducible P1-450 mRNA is correlated with aryl hydrocarbon hydroxylase activity, whereas inducible P3-450 mRNA is correlated with acetanilide 4-hydroxylase activity. This report shows that inducible P3-450 mRNA is also highly correlated with estradiol 2-hydroxylase activity. Both P1-450 and P3-450 activities are induced by 3-methylcholanthrene in liver; in contrast, P1-450 but not P3-450 activity is induced to a significant extent in kidney, lung, and intestine. Constitutive levels of P3-450 mRNA in liver are at least five times greater than those of P1-450 mRNA, thus accounting for the much greater "fold inducibility" of aryl hydrocarbon hydroxylase than acetanilide 4-hydroxylase or estradiol 2-hydroxylase. The hepatic P3-450 induction response occurs at lower inducer concentrations than the P1-450 induction response, suggesting a difference in affinity of the inducer-receptor complex for regulatory regions of the two genes. Developmentally, P1-450 inducibility occurs at least 2 weeks earlier in gestation than P3-450 inducibility, which occurs near the time of birth. These data thus demonstrate striking differences between the expression of two homologous genes in the same P-450 subfamily, with respect to developmental and tissue specificity and sensitivity to common inducers that interact with the Ah receptor.

Animals↗

Partial inhibition of hepatic microsomal aminopyrine N-demethylase by caffeine in partially purified cytochrome P450.

Cytochrome P-450 substrate interactions were studied with cytochrome P-450 partially purified from livers of untreated, phenobarbital-treated, benzo[a]pyrene-treated and caffeine-treated rats. Partial inhibition of aminopyrine N-demethylase in presence of in vitro caffeine observed with intact microsomes was further investigated in a reconstituted system composed of partially purified cytochrome P-450 and cytochrome c reductase. Caffeine addition (in vitro) to partially purified cytochrome P-450 altered the hexobarbital, aniline and ethylisocyanide induced spectral change, and decreased NADPH oxidation in presence of substrates aminopyrine and acetanilide. NADPH oxidation was found to be increased in presence of aminopyrine and unaltered in presence of acetanilide in reconstituted system having partially purified cytochrome P-450 from caffeine-treated rats. Our studies suggest that caffeine acts as a true modifier of cytochrome P-450 and is possibly responsible for the formation of abortive complexes with aminopyrine.

Aminopyrine N-Demethylase↗

Effect of ampicillin on hepatic microsomal mixed-function oxidase system in male mice.

The effect of ampicillin [(D)-alpha-aminobenzyl penicillin] administration on the hepatic mixed-function oxidase (MFO) system was studied in male mice. Ampicillin (100 mg/kg, i.p., 3 days) decreased the levels of cytochrome P-450, aminopyrine N-demethylase, acetanilide hydroxylase and cytochrome c-reductase activity significantly. In carbon tetrachloride (CCl4)-pretreated mice, ampicillin increased acetanilide hydroxylation compared with CCl4 treatment alone; however, all other parameters of the MFO system remained unchanged. Ampicillin exhibited type II binding with microsomes (trough at 388 nm, peak at 430 nm). Thus ampicillin acts as an inhibitor of the MFO system.

Aminopyrine N-Demethylase↗

Alterations in drug metabolising enzymes and lipid peroxidation in different rat tissues by fluoride.

Sodium fluoride at a dose level of 5.0 mg/kg enhanced aminopyrine N-demethylase and NADPH cytochrome c reductase activities and cytochrome P450 and cytochrome b5 levels in rat liver, kidney, lung, intestine and testis, whereas acetanilide hydroxylase activity remained unchanged in kidney and lung and was increased in liver, intestine and testis. Sodium fluoride at 20.0 mg/kg caused a decrease in aminopyrine N-demethylase, acetanilide hydroxylase and NADPH cytochrome c reductase activities and cytochrome P450 and cytochrome b5 levels in all tissues, except for an increase in NADPH cytochrome c reductase activity in the intestine and testis. Fluoride at both dose levels produced only marginal changes in glutathione-S-transferase activity except for a 4-fold increase in the testis at 5.0 mg/kg. Sodium fluoride at 5.0 mg/kg increased lipid peroxidation in all tissues studied. At 20.0 mg/kg there was a decrease in lipid peroxidation in liver, lung and testis and an increase in kidney and intestine.

Animals↗

Effect of caffeine on the hepatic microsomal mixed function oxidase system during phenobarbital and benzo[a]pyrene treatment in rats.

Simultaneous administration of caffeine (100 mg/kg, i.p., 3 days) and phenobarbital (80 mg/kg, i.p., 3 days) to adult male rats resulted in a significant decrease in hepatic cytochrome P-450 and acetanilide hydroxylase activity, compared to phenobarbital administration alone. While simultaneous administration of caffeine and benzo[a]pyrene (20 mg/kg, i.p., 2 days) increased acetanilide hydroxylase, compared to benzo[a]pyrene administration, no change was seen in the cytochrome P-450 concentration. In vitro addition of 2.5 mM caffeine to microsomal incubations from untreated, phenobarbital- and benzo[a]pyrene-treated rats inhibited aminopyrine N-demethylase activity. No significant difference was seen in the extent of aminopyrine N-demethylase inhibition due to the in vitro addition of caffeine to microsomes from untreated or phenobarbital-treated rats, whereas inhibition in microsomes from benzo[a]pyrene-treated rats was greater.

Aminopyrine N-Demethylase↗

Methoxyresorufin: an inappropriate substrate for CYP1A2 in the mouse.

Hepatic microsomes derived from Cypla2(-/-) knockout (KO) and parental strains of mice, C57BL/6N and 129Sv, were used to examine the specificity of methoxyresorufin and acetanilide as substrates for CYP1A2 activity. In addition, animals from each group were exposed to CYP1-inducing compounds. As expected, microsomes from untreated 1a2 KO mice did not have immunodetectable CYP1A2 protein; however, methoxyresorufin-O-demethylase (MROD, 25.5+/-6.1 pmol/min/mg protein) and acetanilide-4-hydroxylation (ACOH, 0.64+/-0.04 nmol/min/mg protein) activities were still present. Furthermore, induction of ethoxyresorufin-O-deethylase (EROD) by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in 1a2 KO mice was accompanied by a greater than 70-fold increase in MROD activity. In contrast, ACOH was only induced 2-fold by TCDD. As with 1a2 KO mice, the parental strains exposed to TCDD or 2,3,4,7,8-pentachlorodibenzofuran (4-PeCDF) showed substantial EROD and MROD induction, whereas ACOH activity was induced to a lesser degree. PCB153 (2,2',4,4',5,5'-hexachlorobiphenyl) resulted in low levels of both EROD and MROD induction. Results indicate that both substrates are subject to metabolism by non-CYP1A2 sources, and the apparent contribution of CYP1A1 activity to methoxyresorufin metabolism makes MROD unsuitable for differentiating CYP1A1 and CYP1A2 activities in the mouse.

Animals↗

Ligand binding studies of engineered cytochrome P-450d wild type, proximal mutants, and distal mutants.

Interactions of various axial ligands with cytochrome P-450d wild type, proximal mutants (Lys453Glu, Ile460Ser), and putative distal mutants (Glu318Asp, Thr319Ala, Thr322Ala) expressed in yeast were studied with optical absorption spectroscopy. P-450d wild type and all five mutants were purified essentially as the high-spin form, but the putative distal mutants contained about 5% low-spin form. Bindings of metyrapone and 4-phenylimidazole to the wild type and all mutants formed nitrogen-bound low-spin forms. In contrast, binding of 2-phenylimidazole to the wild type and most of mutants formed oxygen-bond low-spin forms except for the mutant Glu318Asp in which the nitrogen-bound low-spin form was formed. By analogy with the distal structure of P-450cam, it was thus suggested that Glu318 of P-450d, which corresponds with Asp251 of P-450cam, somehow interacts with 2-phenylimidazole over the heme plane. Addition of 1-butanol and acetanilide, a substrate of P-450d, to the wild type and mutants caused the spin change to the low-spin form. The order of dissociation constants of these oxygen ligands to P-450d was wild type greater than proximal mutants greater than putative distal mutants. Spectral analyses showed that the binding of acetanilide is the same as that of another substrate, 7-ethoxycoumarin, in the putative distal mutants but is not the same in the wild type and proximal mutants. From these findings together with other spectral data, it was suggested that the region from Glu318 to Thr322 is located at the distal region of the heme in membrane-bound P-450d as suggested from the X-ray crystal structure of water-soluble P-450cam and amino acid alignments of P-450s.

Amino Acid Sequence↗

Purification and characterization of six cytochrome P-450 isozymes from human liver microsomes.

Six cytochrome P-450 (P-450) isozymes were purified to electrophoretic homogeneity from the livers of four human organ donors, with three of these isozymes purified from a single individual. Differences were noted between all six P-450s for some or all of the parameters determined by the techniques of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, peptide mapping, spectral analysis of ferrous-carbon monoxide complexes, double-diffusion immunoprecipitin analysis or crossed immunoelectrophoresis (sodium dodecyl sulfate-polyacrylamide gel electrophoresis/peroxidase-coupled staining) with rabbit antisera raised to five of the P-450s, or catalytic activity toward d-benzphetamine, benzo[a]pyrene, acetanilide, debrisoquine, (R)- and (S)-warfarin, and 1-naphthylamine. While NADPH-fortified human liver microsomal preparations showed catalytic activity toward trichloroethylene, 7-ethoxycoumarin, 2-naphthylamine, and 2-aminofluorene in addition to the other substrates mentioned, none of the P-450s which we purified from these microsomes catalyzed the oxidation of these compounds in reconstituted enzyme systems containing purified rat liver NADPH-P-450 reductase. Antibodies raised against one of the purified P-450s inhibited d-benzphetamine N-demethylase activity in microsomal incubations but did not inhibit the metabolism of 7-ethoxycoumarin, acetanilide, benzo[a]pyrene, or debrisoquine. The data provide a strong biochemical basis for the view that distinct isozymes of P-450 exist in humans and that these isozymes differ in catalytic activity toward drugs and carcinogens.

Adult↗

Zwitterionic detergent mediated interaction of purified cytochrome P-450LM4 from 5,6-benzoflavone-treated rabbits with MADPH-cytochrome P-450 reductase.

Hydroxylation of acetanilide catalyzed by purified cytochrome P-450LM4 and NADPH-cytochrome P-450 reductase was reconstituted with the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS). The optimum rate of production of 4-hydroxyacetanilide was observed between 3 and 7 mM CHAPS and was about half that with 0.05 mM dilauroylglyceryl-3-phosphocholine (di-12-GPC). At higher detergent concentrations, hydroxylase activity decreased until at 15-20 mM CHAPS the system was inactive. The effect of CHAPS on the state of aggregation of P-450LM4 and on interaction between the cytochrome and P-450 reductase alone and under turnover conditions was investigated by ultracentrifugation. At 4 mM CHAPS, P-450LM4 was hexameric to heptameric (Mr 369,000). Neither reductase nor reductase plus acetanilide and NADPH altered the state of P-450LM4 aggregation, suggesting that a stable 1:1 P-450/reductase complex did not form under turnover conditions. Replacing CHAPS with 0.05 mM di-12-GPC resulted in formation of heterogeneous P-450 oligomers (Mr greater than 480,000). At CHAPS concentrations where substrate hydroxylation did not occur (15 and 22 mM), P-450LM4 was shown by sedimentation equilibrium measurements to be dimeric and monomeric, respectively. P-450 reductase was shown to reduce monomeric P-450LM4 in the presence of NADPH. Thus, the dependence of hydroxylase activity on [CHAPS] may be related to the state of aggregation of the cytochrome. An apparent correlation between P-450 aggregation state and NADPH-supported hydroxylation was also observed with phenobarbital-inducible P-450LM2 in the presence of detergents [Dean, W.L., & Gray, R.D. (1982) J. Biol. Chem. 257, 14679-14685; Wagner, S.L., Dean, W.L., & Gray, R.D. (1984) J. Biol. Chem. 259, 2390-2395].

Animals↗

Influence of surface composition on the kinetics of alachlor reduction by iron pyrite.

Even though naturally occurring iron sulfide minerals have previously been shown capable of promoting reductive dehalogenations, the role of surface composition has not been fully investigated. Some researchers have proposed that sulfur species represent redox-active moieties on iron pyrite surfaces. Results from this study indicate that neitherthe stoichiometric (100) pyrite surface, nor monosulfide defects, play direct roles in the observed reduction of the herbicide alachlor [2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide]. Pyrite surfaces were initially characterized by X-ray photoelectron spectroscopy (XPS); the samples were then transferred to a liquid cell coupled to the ultrahigh vacuum chamber. Aliquots were periodically removed from the liquid cell to monitor the appearance of the reductive dechlorination product, 2',6'-diethyl-N-(methoxymethyl)acetanilide. In experiments with unaltered pyrite (100) surfaces, rates of reaction decreased over time, even though no change in surface composition could be discerned via XPS. In contrast, ion-bombarded surfaces, which are dominated by monosulfide species, exhibit an initial induction period of low reactivity during which the highly defective surface is oxidized by water. Only after the monosulfide defects undergo oxidation does the rate of alachlor reduction increase, precluding a direct role for these defects as alachlor reductants.

Acetamides↗

Hapten design in the development of competitive enyme-linked immunosorbent assays for genotoxic metabolites of alachlor.

The acetanilide compounds 2-chloro-2',6'-diethylacetanilide (CDA) and 2-hydroxy-2',6'-diethylacetanilide (HDA) are environmental degradative products of the chloroacetanilide herbicide alachlor. CDA, HDA, and alachlor are ground and surface water contaminants. CDA and HDA are genotoxic in bacterial and mammalian test systems. This paper reports hapten design in the development of two competitive enzyme-linked immunosorbent assays (cELISA) for the detection of CDA and HDA. Chloroacetanilide herbicides and other alachlor metabolites that may be present in environmental samples do not cross-react with the detection of CDA and HDA. Solid-phase extraction of CDA and HDA residues from aqueous samples results in a 1000-fold concentration factor, resulting in an effective detection limit of 15 pg/mL for both assays. The specificity of the cELISAs required preservation of the degree of substitution of the acetanilide moiety in the hapten design. The hapten synthesis strategies are suitable for metabolites of other chloroacetanilide herbicides (i.e., acetochlor, butachlor, metolachlor, and propachlor).

Acetamides↗

Renal cortical drug and xenobiotic metabolism following urinary tract obstruction.

Renal cortical metabolism of drugs and xenobiotics was assessed with microsomes prepared from normal, contralateral and 4-day postobstructive hydronephrotic kidneys. Microsomal mixed-function oxidase and prostaglandin H synthase systems were determined in control and 3-methylcholanthrene-treated rabbits. Cytochrome P450 content and biphenyl-4-hydroxylase activity but not cytochrome c reductase activity were reduced in the hydronephrotic kidney. 3-Methylcholanthrene treatment increased cytochrome P450 content and biphenyl-4-hydroxylase and acetanilide-4-hydroxylase activities in normal, contralateral, and hydronephrotic kidneys. However, even after 3-methylcholanthrene treatment, hydronephrotic kidney cytochrome P450 content and acetanilide-4-hydroxylase activity were not more than 20% of the corresponding normal kidney values. Prostaglandin H synthase metabolism of benzidine was observed in the hydronephrotic kidney but was at the limit of detection in normal or contralateral kidneys with or without 3-methylcholanthrene treatment. Characteristics of benzidine metabolism were consistent with the hydroperoxidase rather than the fatty acid cyclooxygenase activity of prostaglandin H synthase. Therefore, hydronephrosis alters the drug and xenobiotic metabolic profile of the renal cortex from a primarily mixed-function oxidase-dependent system to one with the potential for metabolism by the hydroperoxide component of prostaglandin H synthase.

Animals↗

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.

Aniline Compounds↗