bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties of an N,N‐dimethyl‐p‐aminoazobenzene Oxide Reductase Purified from Rat Liver Cytosol
Authors: Johnson Pamela R. Lashmet , Ziegler D. M. 
Published: October 2006

AbstractHomogenates of all rat tissues examined, except brain, catalyze reduction of N,N‐dimethyl‐p‐aminoazobenzene N‐oxide (DMAB N‐oxide) to N,N‐dimethyl‐p‐aminoazobenzene by NADPH. Liver is the most active, and about one third of the homogenate activity of this tissue is recovered in the cytosol fraction. The purified cytosol enzyme has the properties of a tetrameric protein (Mr 370,000) consisting of identical subunits free from chromophores that absorb in the visible spectrum and from metals or other detectable prosthetic groups. The purified reductase is also free from NADPH oxidase and from cytochrome c or azo reductase activities. The enzyme is quite specific for NADPH as reductant and DMAB N‐oxide as the electron acceptor. Reduction of other N,N‐dimethyl‐arylamine or alkylamine oxides as well as N‐methylheterocyclicamine oxides could not be detected. Analysis of kinetic data indicate that, at saturating concentrations of the other substrate, 21 μM NADPH and 700 μM DMAB N‐oxide are required for half maximal velocity. At infinite concentrations of both substrates the turnover is 150 min−1 at 37 °C.
Oxidative metabolism of some hydrazine derivatives by rat liver and lung tissue fractions
Authors: Erikson John M. , Prough Russell A. 
Published: October 2006

AbstractThe enzyme systems in rat liver and lung responsible for the oxidative metabolism of hydrazine derivatives were studied to determine whether these enzymes, cytochrome P‐450 and monoamine oxidase, were responsible for metabolically activating hydrazines to carcinogenic/toxic metabolites. Cytochrome P‐450 preferentially oxidized the nitrogen to nitrogen bond of 1,2‐disubstituted hydrazines and hydrazides, while monoamine oxidase oxidized the nitrogen to nitrogen bond of all the classes of hydrazine derivatives that were tested. Oxidation of the nitrogen to nitrogen bond led to the formation of stable azo intermediates in the case of 1,2‐disubstituted hydrazines and to unstable monoazo (diazene) metabolites in the case of monosubstituted hydrazines and hydrazides. In addition, cytochrome P‐450 preferentially oxidized the carbon to nitrogen bond of monoalkylhydrazines; this reaction resulted in the formation of aldehyde metabolites (via hydrazone intermediates).Monosubstituted hydrazines were shown to be potent, irreversible inhibitors of mitochondrial monoamine oxidase. In contrast, the 1,2‐disubstituted hydrazines appeared to be good substrates for the monoamine oxidase and served as competitive inhibitors at high concentrations. There did not appear to be any monoamine oxidase isozyme (form A or B) specificity in the metabolism of either the 1,2‐disubstituted hydrazines or the monoalkylhydrazines, ethyl‐ and n‐propylhydrazine.
Biochemical interactions of carbamates and ecothiophate with the activated conformation of nicotinic acetylcholine receptor
Authors: Mansour Nabil A. , Valdes James J. , Shamoo Adil E. , Annau Zoltan 
Published: October 2006

AbstractPurified Torpedo nobiliana electric organ acetylcholine receptor (AChR) was reconstituted into membranes containing natural phospholipids supplemented with cholesterol (25% w/w). The reconstituted system facilitates the study of the effects of drugs on the regulation of the AChR channel complex under both resting and carbachol (carb)‐stimulated conditions. Neostigmine (Neo) was the only carbamate to induce activation of [3‐H]‐phencyclidine ([3‐H]‐PCP) binding to the channel sites, acting as a weak agonist. The activation of [3‐H]‐PCP binding is dependent upon the nature of the reconstituted systems, with carb/Neo activation ratios of 8, 3, and 1 for the intact purified AChR vesicles fraction (PVF), the PVF reconstituted in phospholipid/cholesterol (CRPVF), and the PVF reconstituted in phospholipid (RPVF), respectively. The carbamates Neo, physostigmine (Physo), and pyridostigmine (Pyrido) inhibited carb‐activated [3‐H]‐PCP binding with Ki values of 10, 20, and 1,600 μM, respectively. The inhibition was mixed competitivenoncompetitive in nature. The characteristic response of CRPVF to carb‐stimulated [22‐Na] influx was inhibited by the three carbamates, with IC‐50 values of 6,50, and 1,000 μM for Neo, Physo, and Pyrido, respectively. The quaternary ammonium organophosphate ecothiophate (Eco) inhibited carb‐stimulated [22‐Na] influx with potency similar to that of Neo. Preincubation of AChR preparation with the carbamates and ecothiophate caused a reduction in the binding of [125‐I]‐α‐ bungarotoxin ([125‐I]‐α‐BGT) with the following decreasing order of potency: Neo < Physo < Eco < Pyrido. Calcium has a direct modulatory role on the time‐course inhibition of [125‐I]‐α‐BGT binding by these drugs. While we observed a high potency of Neo and Physo in inhibiting [125‐I]‐α‐BGT binding, it was undetectable for the carbamate insecticide 2‐methyl‐2‐(methylthio)propionaldehyde‐O‐(methylcarbamoyl)oxime (aldicarb). These data suggest that the potent anticholinesterase carbamate agents interact differently with the AChR and its ionic channel. Their interactions with the nicotinic AChR channel system can be described as (a) weakly agonist, (b) directly acting on the open conformation of the channel, and (c) blocking the AChR‐binding sites.
Influence of Bipyridylium Compounds on Microsomal Mixed‐Function Oxidation Activities
Authors: Zychlinski Lech , Raska‐Emery Patricia , Montgomery Mark R. 
Published: October 2006

AbstractThe two principal bipyridyl herbicides, paraquat and diquat, were investigated for their influence on microsomal mixed‐function oxidation (MFO) activities and on NADPH oxidation rates in lung, liver, and kidney preparations. In lung microsomal preparations, benzphetamine N‐demethylation was found to be inhibited by paraquat and diquat in a concentration‐dependent manner, but ethylmorphine N‐demethylation was unaffected by these bipyridyls. In liver microsomal fractions, both benzphetamine and ethylmorphine N‐demethylases were inhibited by paraquat and diquat. Neither bipyridyl affected MFO activity in kidney preparations. A kinetic investigation of the enzyme inhibition showed that only Vmax was affected by paraquat and diquat, providing the first evidence for noncompetitive inhibition by the bipyridyls. In all microsomal preparations, NADPH oxidation was stimulated significantly by paraquat and to an even greater extent by diquat in the absence or presence of benzphetamine or ethylmorphine. The influence of MFO substrates on the stimulation varied widely among the three organ systems. In lung, paraquat‐ or diquat‐mediated stimulation of NADPH oxidation was equal in the absence of MFO substrates and in the presence of ethylmorphine, but the stimulation was increased in the presence of benzphetamine. Stimulation of NADPH oxidation by the bipyridyls, in liver as well as in kidney preparations, was equal in all situations in the absence of MFO substrates and in the presence of benzphetamine or ethylmorphine, although the quantity of this stimulation was greater in liver than in kidney fractions. It is apparent that the bipyridyls are potent stimulators of in vitro NADPH oxidation in microsomal preparations from several organs. The quantity of the NADPH oxidation stimulation seems to be a decisive factor in the inhibition of xenobiotic metabolism. Whether the stimulation of NADPH oxidation and the noncompetitive inhibition of xenobiotic metabolism play a significant role in bipyridyl toxicity are under further investigation.
Liver Cell Calcium Homeostasis in Carbon Tetrachloride Liver Cell Injury: New Data With Fura21
Authors: Dolak James A. , Waller Robert L. , Glende Eric A. , Recknagel Richard O. 
Published: October 2006

AbstractThe calcium fluorescent probe fura2 was used to measure concentration of free calcium in the cytosol of isolated rat hepatocytes in suspension. The resting level in untreated hepatocytes was 121 nM. On addition of CCl4 at a concentration of 0.5 mM, cytosolic free calcium rose sharply and reached a statistically significant (P<0.05) steady plateau level of about 190 nM within five minutes. With a concentration of 1.0 mM CCl4, cytosolic free calcium rose within ten minutes to a plateau level of about 200 nM. Use of fura2, along with the capacity of Mn2+ ions to effectively quench fura2 fluorescence, provided the basis for a simple and decisive method to determine whether the added CCl4 was permeabilizing the hepatocyte plasma membrane by direct solvent action. It was found that up to a concentration of 1.0 mM, CCl4 did not permeabilize the plasma membrane, but direct attack on the plasma membrane was unequivocally demonstrated for concentrations of 2 mM CCl4 and above. Finally, an hypothesis is presented for resolution of the puzzling dilemma that emerged from the observation, reported from two laboratories, that CCl4 can rapidly mobilize liver mitochondrial calcium despite the well‐known relative resistance of these organelles to the damaging effects of this toxic agent.
Chromatographic and catalytic properties of multiple forms of rabbit pulmonary cytochromes P‐450
Authors: Ueng Tzuu‐Huei , Peiperl Martha D. , Alvares Alvito P. 
Published: October 2006

AbstractRabbit pulmonary cytochrome P‐450 forms 2,5, and 6 were resolved using anion‐exchange high‐performance liquid chromatography (HPLC) and their properties compared with rabbit liver cytochrome P‐450 isozymes LM2 and LM6. Although rabbit pulmonary form 2 and liver LM2 had similar electrophoretic mobilities and similar substrate specificities in reconstitution experiments, they differed in their HPLC elution profiles. High‐performance liquid chromatography of pulmonary microsomes from rabbits treated with 3‐methylcholanthrene (3‐MC) revealed the induction of form 6 isozyme, which had a retention time, electro‐phoretic mobility, and substrate specificity similar to those of rabbit liver LM6. In reconstitution experiments, forms 2 and 6 showed the highest substrate specificities toward benzphetamine and 7‐ethoxyresorufin, respectively. Rabbit lung cytochrome P‐450 form 5 was relatively inactive toward all substrates tested.
Lack of inducibility of brain monooxygenase activities including parathion desulfuration
Authors: Chambers Janice E. , Forsyth Carol S. 
Published: October 2006

AbstractThe ability of phenobarbital and β‐naphthoflavone to induce parathion desulfuration, aminopyrine N‐demethylation, and NADPH–cyto‐chrome‐c reductase activity in the brain and liver of male and female rats was investigated. Activities of all three enzymes were found in similar levels in both the mitochondrial and microsomal fractions of brain. There were no sex differences in brain activities. Liver activities were from 10‐ to 30‐fold higher than brain activities when computed on a tissue‐wet‐weight‐equivalent basis. Although exposure to both inducers increased all three enzyme activities and cytochrome P‐450 in liver, neither inducer increased the enzyme activities in mitochondrial or microsomal brain fractions of either sex. Thus, these brain monooxygenase activities appear to be refractory to induction by two classical types of cytochrome P‐450 inducers. This lack of inducibility could serve to protect the animal against environmentally enhanced increases in the activation of xenobiotics to neurotoxic metabolites, such as parathion desulfuration to paraoxon.
Drug‐induced protoporphyria in the olfactory mucosa of the hamster
Authors: Reed Celia J. , van den Broeke Leon T. , De Matteis Francesco 
Published: October 2006

AbstractAdministration of 3,5‐diethoxycarbonyl‐4‐ethyl‐1,4‐dihydro‐2,6‐dimethylpyridine (4‐ethyl‐DDC) to hamsters resulted in a marked loss of cytochrome P‐450‐dependent reactions (peroxidase, 7‐ethoxycoumarin O‐deethylase, and 7‐ethoxyresorufin O‐deethylase) in both liver and olfactory epithelium within 2 hr. This inactivation of cytochrome P‐450 was accompanied by inhibition of ferrochelatase (FK), stimulation of 5‐aminolevulinate synthase (ALA‐S), and accumulation of protoporphyrin both in the liver and to a lesser degree, in the olfactory epithelium. These results suggest that the mechanism of induction of protoporphyria in nasal tissues is similar to that occurring in the liver, namely, suicidal metabolism of 4‐ethyl DDC by cytochrome P‐450 resulting in formation of N‐ethylprotoporphyrin, a potent inhibitor of FK. The consequent depletion of heme leads to stimulation of ALA‐S and, thus, porphyrin accumulation. Investigation of the dose‐response to 4‐ethyl DDC demonstrated that, in liver, maximal inhibition of FK and accumulation of protoporphyrin occurred at a dose of 50 mg/kg while ALA‐S activity continued to increase up to a dose of 100 mg/kg. This is compatible with an additional effect of the drug on ALA‐S involving induction of cytochrome P‐450 and, thus, further depletion of heme. In the olfactory epithelium, stimulation of ALA‐S was significantly less marked, suggesting that this secondary effect does not operate in nasal tissue. This is consistent with reports that olfactory cytochrome P‐450s are noninducible.
Induction of phosphatidylcholine biosynthesis via cdpcholine pathway in lung and liver of rats following intratracheal administration of ddt and endosulfan
Authors: Narayan Satya , Dani H. M. , Misra U. K. 
Published: October 2006

AbstractThe induction of phosphatidylcholine (PC) biosynthesis via the CDPcholine pathway in lung and liver of rats has been shown following the intratracheal administration of 1,1,1‐trichloro‐2m2‐bis(p‐chlorophenyl) ethane (DDT) (5 mg/100 g body weight) and endosulfan (1 mg/100 g body weight) for 3 days. Controls received only the vehicle solution (groundnut oil, 0.1 ml/100 g body weight). The treatment of DDT and endosulfan significantly increased the PC contents and the incorporation of radioactive [methyl‐3H]choline into PC of lung and liver microsomes. The incorporation of radioactive [methyl‐14C]methionine into microsomal PC of lung and liver was not affected significantly by treatment with either of the insecticides. 1,4,5,6,7‐hexachloro‐5‐norbornene‐2,3‐dimethano cyclic sulfite (endosulfan) administration significantly increased the activity of choline kinase and phosphocholine cytidylyl‐transferase (both cytosolic and microsomal) of lung, whereas DDT increased the activity of only the latter. In liver, both DDT and endosulfan administration significantly increased the activity of choline kinase and phosphocholine cytidylyltransferase (both cytosolic and microsomal). However, the activity of phosphocholinetransferase was not affected in both lung and liver microsomes of rats treated with these insecticides. The PC precursor pool sizes, choline and phosphorylcholine, of lung and liver tissues were not altered by DDT and endosulfan treatments. The present results suggest that the increased level of PC and incorporation of radioactive [methyl‐3H]choline into microsomal PC could be the result of increased activity of choline kinase and phosphocholine cytidylyltransferase of lung and liver of rats following intratracheal administration of DDT and endosulfan.
Acetaminophen metabolism in vivo by pregnant, fetal, and neonatal guinea pigs
Authors: Ecobichon D. J. , Hidvegi S. , Comeau A. M. , Varma D. R. 
Published: October 2006

AbstractAcetaminophen (50 mg/kg body weight) was administered by iv injection to pregnant guinea pigs (60–65 days of gestation) and by ip injection to cesarian‐derived term (67 days of gestation) pups. At suitable time intervals after treatment, the concentrations of drug, glucuronide (GLU), and sulfate (SO4) in blood plasma, urine, and bile were measured by high‐performance liquid chromatography (HPLC). At 60–65 days of gestation, guinea pig fetuses formed both GLU and SO4, an approximate ratio of 2:1 being observed with mean concentrations of the order of 43 and 27 μg/mL being measured for GLU and SO4, respectively at 180 min post‐treatment. At the same time interval, the major detoxification product found in the blood plasma of the pregnant dams was GLU (104 μg/mL) with only minute amounts (4.2 μg/mL) of SO4 being detected. In cesarian‐derived and acetaminophen‐treated pups, euthanized at 2 or 4 hr post‐treatment, plasma levels of GLU were approximately twofold higher relative to the concentration of SO4 at both time intervals. Significant differences were not observed in either bile or urine at 2 hr post‐treatment but by 4 hr after treatment the levels of GLU found in the bile and urine were two‐ or threefold higher than those of SO4. In contrast to the adult guinea pig where GLU forms some 90% of the urinary excretory product and SO4 accounts for only 7%, the SO4 pathway of detoxification appears to be of significant importance to the fetal and neonatal animal.
The sulfur‐cyanolysis sites of serum albumin: Metabolite competition studies
Authors: Jarabak Rebecca , Westley John 
Published: October 2006

AbstractIn the presence of a source of sulfane sulfur, a cyanolysis reaction catalyzed by serum albumin may contribute to cyanide detoxication. The active site for this catalysis by serum albumin has been investigated in competition studies with ligands that have known albumin binding sites. Despite complications caused by the occurrence of multiple primary and secondary sites for many ligands, the results show that the primary sites for bilirubin, steroids, indoles, aspirin, and palmitate are distinct from that for sulfur. Laurate is a tight‐binding partial inhibitor of the cyanolysis reaction, competitive with cyanide rather than with sulfur. In view of the formal mechanism previously established for the catalyzed reaction, this result indicates that the sulfur‐cyanolysis site is probably near the site occupied by laurate.
The role of enteric bacteria in the anerobic metabolism of 5‐aminosalicylate
Authors: Tucker Mark A. , Bisesi Michael S. , Smith Timothy J. 
Published: October 2006

AbstractThe primary (and inactive) enteric metabolite of 5‐aminosalicylate is N‐acetyl‐5‐amino‐salicylate. Previous studies have demonstrated acetylation of this anti‐inflammatory agent by intestinal and bacterial homogenates. To assess the contribution of anerobic bacteria to the N‐acetylation in vivo, we have measured the production of N‐acetyl‐5‐aminosalicylate in anerobic microculture. Our results indicate that enteric bacteria play a minor role in N‐acetylation, but may contribute to the production of other metabolites of pharmacologic and toxicological interest.
Multiple Pathways for the Oxidative Metabolism of Estrogens in Syrian Hamster and Rabbit Kidney
Authors: Degen G. H. , Blaich G. , Metzler M. 
Published: October 2006

AbstractMicrosomal preparations from hamster kidney, a target tissue for the carcinogenic action of stilbene‐type and steroidal estrogens, catalyze the oxidative metabolism of diethylstilbestrol (DES). The formation of the major metabolite Z,Z‐dienestrol and of reactive intermediates capable of protein binding were mediated by enzyme activities requiring nicotinamide‐adenine dinucleotide phosphate (reduced form‐NADPH), cumene hydroperoxide, or arachidonic acid (ARA). In addition, hydroxylated DES metabolites were detected in NADPH‐supplemented incubations. The NADPH‐dependent oxidation of DES was inhibited by SKF 525A and metyrapone. Monooxygenase‐catalyzed metabolism was apparently responsible for the majority of DES oxidation in microsomes from whole hamster kidneys in vitro and this activity is preferentially localized in the kidney cortex. However, ARA‐dependent, i.e., prostaglandin H synthase (PHS) mediated oxidation of DES and of the catechol estrogen 2‐hydroxyestrone was demonstrated as well in the medulla of both rabbit and hamster kidney. It is proposed that monooxygenase and PHS activities act in concert in the metabolic activation of carcinogenic estrogens. This appears to apply in particular to steroidal estrogens, since catechol estrogens formed by monooxygenases are further oxidized to reactive intermediates by PHS and other peroxidatic enzymes.
Strain and sex differences in the response of mice to drugs that induce protoporphyria: Role of porphyrin biosynthesis and removal
Authors: Holley Anne , King L. J. , Gibbs A. H. , de Matteis F. 
Published: October 2006

AbstractA hepatic green pigment, inhibitory toward ferrochelatase, has been isolated from the liver of mice treated with griseofulvin, isogriseofulvin, or 3,5‐diethoxycarbonyl‐1,4‐dihydrocollidine and has been shown to exhibit identical chromatographic characteristics to authentic N‐methyl protoporphyrin. All four possible structural isomers have been demonstrated, and each drug produced primarily the same isomer. N‐Methyl protoporphyrin has also been found in very small amounts in the liver of untreated mice, but the isomeric composition appeared to differ from that of the drug‐induced N‐methyl protoporphyrin.Intraperitoneal administration of 3,5‐diethoxycarbonyl‐1,4‐dihydrocollidine to female C3H / He / Ola and NIH / Ola inbred mice produced a marked dose‐related loss of hepatic ferrochelatase activity, which was identical in magnitude in the two strains. Induction of hepatic 5‐aminolevulinate synthase (ALA‐S), and accumulation of liver protoporphyrin, however, were greater in C3H / He / Ola mice. The strain difference in ALA‐S response was most marked when inhibition of ferrochelatase (the “specific” effect of the drug) was maximal, and this suggests that a genetic variation exists in the sensitivity of ALA‐S to a second drug action, the so‐called nonspecific action, which is shared by many lipid‐soluble compounds.Male mice of three strains accumulated greater amounts of hepatic protoporphyrin than females after treatment with griseofulvin, yet no significant difference was found between the two sexes in the extent of ferrochelatase inhibition. Stimulation of ALA‐S activity was slightly greater in males, but when porphyria was very marked, ALA‐S activities were significantly lower in this sex. Our results indicate a biphasic relationship between ALA‐S activity and porphyrin accumulation, with a depression of the activity of the enzyme occurring at high liver protoporphyrin concentrations.
Oxidant injury increases cell surface receptor binding of angiotensin ii to pulmonary artery endothelial cells
Authors: Patel J. M. , Madhavi Sekharam K. , Block Edward R. 
Published: October 2006

AbstractNitrogen dioxide (NO2), an environmental oxidant, is known to activate phospholipase A1 and modulate the plasma membrane structure of porcine pulmonary artery endothelial cells. We evaluated the effects of exposure to NO2, purified phospholipase B (which acts as phospholipase A1 and A2), or phospholipase A2 on 125I‐angiotensin II (Ang II) receptor binding, internalization, or both in pulmonary endothelial cells. Exposure to 5 ppm NO2 for 48 hr at 37°C or 0.075 U each of phospholipase B or A2 in phosphate‐buffered saline (PBS) for 30 min at 24°C resulted in an increase in total Ang II binding (i.e., cell surface bound and internalized) by 45% (p <0.05), 50% (p <0.05), and 85% (p <0.001), respectively, compared to controls. An Ang II receptor antagonist, [Sar1 IIe8] Ang II, competitively displaced Ang II binding to control, NO2‐, phospholipase B‐, and phospholipase A2‐exposed cells. Dissociation of bound Ang II in the presence of PBS was <1% of total bound Ang II in control, NO2‐, and phospholipase B‐exposed cells and was 50% of total bound Ang II in phospholipase A2‐exposed cells. In the presence of isotonic acetic acid/NaCl, in excess of 90% of cell surface‐bound Ang II was dissociated from control, NO2‐, and phospholipase B‐exposed cells, and there was <2% of Ang II detectable when acid‐treated cells were subjected to NaOH solubilization. In cells exposed to phospholipase A2, acetic acid treatment did not release cell‐bound Ang II, and the remaining Ang II was recovered in the NaOH solubilized fraction. These results demonstrate that NO2 exposure results in increased cell surface receptor binding and not internalization of Ang II and that phospholipase B‐but not phospholipase A2‐induced modulation of the membrane structure mimicked the effect of NO2 on Ang II binding in pulmonary endothelial cells.