bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diethylstilbestrol potentiates and testosterone antagonizes the action of 3‐methylcholanthrene on benzo(a) pyrene metabolism in hep G2 cells
Authors: Moore Susan Mcafee , Lamartiniere Coral A. 
Published: October 2006

AbstractWe have used the human hepatoma cell line, Hep G2, to examine the ability of hormones and xenobiotics to modulate the hepatic induction of benzo(a)pyrene hydroxylase and epoxide hydrolase. Hep G2 cells were cultured in Eagle's Minimum Essential Medium supplemented with 10% fetal calf serum. 3‐Methylcholanthrene, diethylstilbestrol, testosterone propionate, and combinations of 3‐meth‐ylcholanthrene, and each of the hormones were added directly to the culture media. We subsequently studied the metabolism of benzo(a)pyrene using cell lysates of the Hep G2 cells. Metabolites were quantitated by high‐performance liquid chromatography (HPLC) using fluorodetection. Exposure to 3‐methyl‐cholanthrene alone resulted in an eightfold increase in total benzo(a)pyrene metabolites with a change of the predominant metabolite from the 3‐hydroxy‐benzo(a)pyrene to the carcinogenic pathway of the benzo(a)pyrene‐7,8‐diol. Diethylstilbestrol and testosterone propionate resulted in small, but significant, decreases in metabolism of benzo(a)pyrene. When exposed in combination with 3‐methyl‐cholanthrene, testosterone propionate antagonized and diethylstilbestrol potentiated the metabolism of benzo(a)pyrene. 3‐Methylcholanthrene, diethylstilbestrol, and combinations of 3‐methylcholanthrene and diethylstilbestrol or testosterone propionate resulted in increased epoxide hydrolase activity as compared to controls. These results, carried out in a human hepatoma cell line, lend support to a concern for potentiated toxicity and carcinogenicity following exposure to complex chemical mixtures.
Spectroscopic quantitation of cytochrome P‐450 in human lung microsomes
Authors: Wheeler Clyde W. , Guenthner Thomas M. 
Published: October 2006

AbstractThe cytochrome P‐450 content of human lung microsomes was measured by difference spectroscopy of the carbon monoxide‐complexed hemoprotein. These measurements were only possible after the microsome preparation had been subjected to centrifugation over a discontinuous sucrose gradient, to remove an opaque black contaminant. The specific concentration of total cytochrome P‐450 in human lung microsomes is essentially identical to that of microsomes prepared under identical conditions from untreated baboon lungs, but is only 0.7% of the specific content found in lung microsomes from untreated rabbits. These measurements correspond well to the observed metabolic capacities of the various microsome samples.
Role of lipid metabolism in cell killing by calcium plus ionophore A23187
Authors: Shier W. Thomas , Dubourdieu Daniel J. , Wang Huei‐Hsiang L. 
Published: October 2006

AbstractCultured fibroblasts treated with divalent cation ionophore A23187 in the presence of extracellular calcium provide a useful model system for studying mechanisms of cell death associated with elevated intracellular calcium concentrations. Cell death induced by A23187 plus calcium can be conveniently monitored as membrane permeabilization to Trypan blue dye. Because lipids are a major component of cell membranes and play an important role in determining membrane permeability, the present study was initiated to identify changes in cell lipid composition that occur during membrane permeabilization induced by calcium plus A23187. The percent label in each of the major structural lipids in biosynthetically labeled NIH3T3 fibroblasts changed < 10% during the time course of membrane permeabilization. During the course of membrane permeabilization there was significantly increased label in lysophosphatidylinositol and lysophosphatidylcholine and reduced label in phosphatidylinositol 4,5‐bisphosphate. The time course of these changes corresponded to that of the arachidonic acid release response stimulated by calcium plus A23187, not to the time course of membrane permeabilization, which occurs later. These observations are consistent with lipid metabolism induced by A23187 plus calcium playing only a possible regulatory or intermediatory role in membrane permeabilization, rather than causing direct permeabilization of the lipid phase of the membrane.
Characterization of covalent binding of [14C]‐2‐chloro‐4‐acetotoluidide to microsomes of starling liver and kidney
Authors: Giri Shri N. , Siegel David M. 
Published: October 2006

AbstractIn this study, we have characterized the covalent binding of [14C]‐2‐chloro‐4‐acetotoluidide (CAT) radioactivity to microsomes of starling liver and kidney. The maximal velocity (Vmax) of covalent binding and apparent Michaelis constant (Km) for both tissues were similar. The Vmax for liver and kidney were 52.8 and 68.9 pmol/min/mg protein, and the apparent Kms were 0.54 and 0.87 mM, respectively. The covalent binding of radioactivity to heat‐denatured microsomes of liver and kidney was reduced by 62% and 15%, respectively. Incubation at 0°C reduced the binding by 80% to liver and 70% to kidney microsomes. Absence of nicotinamide adenine dinucleotide phosphate (NADP) and molecular O2 reduced the binding to liver microsomes by 36 and 53%, as opposed to 28% increase and 26% decrease in binding to kidney microsomes, respectively. Inducers of cytochrome P450 monooxygenase (P450), phenobarbital, and 3‐methylcholanthrene (3‐MC), had opposite effects on the covalent binding of [14C]‐CAT radioactivity to hepatic and renal microsomes. Phenobarbital increased the binding to hepatic microsomes by 100% and had no effect on binding to renal microsomes. 3‐MC, on the other hand, increased the binding to kidney microsomes by threefold and had no effect on the binding to hepatic microsomes. SKF 525A, an inhibitor of P450, inhibited the binding to hepatic microsomes by 60% at 0.5 mM but failed to have any effect on binding to renal microsomes. α‐Naphthoflavone, another inhibitor of P450, had no effect on the covalent binding of [14C]‐CAT radioactivity to microsomes of either tissue. Addition of cysteine and glutathione in the incubation mixture inhibited the covalent binding of radioactivity to both liver and kidney microsomes in a concentration‐dependent manner. It was concluded that hepatic and renal microsomes of starling behave differently with respect to the effects of P450 inducers and inhibitors, heat denaturation, NADPH dependence, and presence of molecular oxygen on bioactivation of [14C]‐CAT and its subsequent covalent binding to microsomal proteins.
In vitro inhibition of rat platelet aggregation by ochratoxin A
Authors: Omar Rabeea F. , Randell Edward , Rahimtula Anver D. 
Published: October 2006

AbstractThe mycotoxin ochratoxin A (OA) consists of 5‐chloro‐3‐methyl‐3,4‐dihydro‐8‐hydroxyisocoumarin moiety linked by an amide bond to β‐L‐phenylalanine. When added to washed rat platelets in vitro, OA caused a dose‐dependent inhibition of aggregation induced by agonists such as adenosine diphosphate (ADP) or thrombin. The aggregatory response induced by prior addition of an agonist was also reversed in a dose‐dependent manner by OA. Inhibition of aggregation appeared to be irreversible since exposure of platelets to OA followed by several washings removed most of the mycotoxin associated with the platelets but did not diminish the inhibitory response. Serotonin secretion from dense granules and arachidonic acid release from membrane phospholipid (especially phosphatidylcholine) as well as its further metabolism were also inhibited by OA. These results suggest that a disruption of the platelet plasma membrane structure by OA is probably responsible for inhibition of the primary and secondary phases of aggregation.
Lack of desensitization of muscarinic receptor–mediated second messenger signals in rat brain upon acute and chronic inhibition of acetylcholinesterase
Authors: Abdallah Elsayed A. M. , El‐Fakahany Esam E. 
Published: October 2006

AbstractWe studied the effects of acute and chronic in vivo inhibition of acetylcholinesterase on both the density and function of brain muscarinic cholinergic receptors. Adult male rats were treated either once or multiple times over a period of 10 days with the irreversible acetylcholinesterase inhibitor diisopropylfluorophosphate (DFP). The concentration and affinity of muscarinic receptors in various brain regions were determined using radioligand binding techniques. Acute DFP treatment resulted in a significant reduction in receptor number only in the brain stem, while chronic treatment caused receptor downregulation in the brain stem, cerebral cortex, and striatum. There was no change in ligand affinity in any of the brain regions. In sharp contrast, muscarinic receptor function was fully preserved, in terms of coupling of the receptors to increased phosphoinositide hydrolysis in the cerebral cortex, hippocampus, and striatum, or inhibition of cyclic AMP formation in the cerebral cortex or striatum. Therefore, there is a marked lack or correlation between DFP‐induced muscarinic receptor down‐regulation and receptor desensitization.
Intracellular calcium chelators and oxidant‐induced renal proximal tubule cell death
Authors: Schnellmann Rick G. 
Published: October 2006

AbstractThe effect of intracellular calcium chelators on rabbit renal proximal tubule (RPT) cell death induced by t‐butyl hydroperoxide (TBHP) and H2O2 was examined. Preincubation of RPT suspensions with 50 μM QUIN 2/AM completely prevented TBHP (0.5 mM) and H2O2 (2 mM) induced cell death [i.e., release of lactate dehydrogenase (LDH)]. QUIN 2/AM, BAPTA/AM, EGTA/AM, and FURA 2/AM, at 5 μM, decreased LDH release (at 6 hr) from 41% to 4%, 21%, 26%, and 33%, and decreased lipid peroxidation (at 1 hr) from 1.0 to 0.1, 0.4, 0.6, and 0.8 nmol MDA/mg protein, respectively, after TBHP exposure. Since oxidant‐induced lipid peroxidation and cell death are iron‐dependent in this model, these results suggest that the intracellular calcium chelators inhibit cell death by chelating iron.
Modulation of transcription in rat liver nuclei in vitro by a diol epoxide of benzo[a]pyrene
Authors: Shah G. M. , Bhattacharya R. K. 
Published: October 2006

AbstractTreatment of isolated rat liver nuclei with 7β, 8α‐dihydroxy‐9α, 10α‐epoxy‐7, 8, 9, 10‐tetrahy‐drobenzo[a]pyrene, the ultimate carcinogenic metabolite of benzo[a]pyrene, resulted in inhibition of transcription as measured by radioactive precursor incorporation into RNA. The mechanism of inhibition as analyzed by use of different types of inhibitors suggested that the carcinogen acted on both the major components of transcription machinery, that is, the template chromatin and the enzyme RNA polymerases. This action correlates well with the observations made after administration of benzo[a]pyrene to rats.
Effect of N‐methyl‐N′‐Nitro‐N‐nitrosoguanidine on amino acid incorporation into mucosal protein of rat stomach
Authors: Bagewadikar R. S. , Bhattacharya R. K. 
Published: October 2006

AbstractAdministration of the carcinogenic N‐nitroso compound, N‐methyl‐N′‐nitro‐N‐nitrosoguanidine in drinking water (0.5 mg/mL) to male Wistar rats for 1 week caused impairment of in vivo and in vitro incorporation of [14C]leucine into stomach mucosal protein. This impairment gradually returned to normal after 4 weeks. Uptake of [14C]leucine into mucosal protein was significantly inhibited after in vitro treatment of stomach mucosa with the carcinogen. Addition of the N‐nitroso compound in a cell‐free system using postmitochondrial supernatant prepared from stomach mucosa also showed inhibition of amino acid incorporation. Using a more defined system consisting of purified polyribosome from stomach mucosa and pH 5 enzyme fraction derived from liver it was further demonstrated that the carcinogen purturbed protein synthesizing ability of polyribosome, under both in vivo and in vitro treatment conditions. In these respects this carcinogen has similar action on the target tissue of stomach as in the liver, although the in vivo effect may be related more to toxicity than carcinogenicity.
Regulation of two electrophoretically distinct proteins recognized by antibody against rat liver cytochrome P450 3A1
Authors: Gemzik Brian , Greenway Denise , Nevins Cheryl , Parkinson Andrew 
Published: October 2006

AbstractWe recently reported that antibody against purified P450 3A1 (P450p) recognizes two electrophoretically distinct proteins (50 and 51 kDa) in liver microsomes from male and female rats, as determined by Western immunoblotting. Depending on the source of the liver microsomes, the 51‐kDa protein corresponded to 3A1 and/or 3A2 which could not be resolved by sodium dodecyl sulfate (SDS)polyacrylamide gel electrophoresis. The other protein (50 kDa) appears to be another member of the P450 IIIA gene family. Both proteins were markedly intensified in liver microsomes from male or female rats treated with pregnenolone‐16α‐carbonitrile, dexamethasone, troleandomycin, or chlordane. In contrast, treatment of male or female rats with phenobarbital intensified only the 51‐kDa protein. Treatment of male rats with Aroclor 1254 induced the 51‐kDa protein, but suppressed the 50‐kDa form. In addition to their changes in response to inducers, the 50‐ and 51‐kDa proteins also differed in their developmental expression. For example, the 50‐kDa protein was not expressed until weaning (3 weeks), whereas the 51‐kDa protein was expressed even in 1‐week‐old rats. At puberty (between weeks 5 and 6), the levels of the 50‐kDa and 51‐kDa proteins markedly declined in female but not in male rats, which introduced a large sex difference (male > female) in the levels of both proteins. Changes in the level of the 51‐kDa protein were paralleled by changes in the rate of testosterone 2β, 6β‐, and 15β‐hydroxylation. In male rats, the marked increase in the levels of the 50‐kDa protein between weeks 2 and 3 coincided with a three‐ to four fold increase in the rate of testosterone 2β‐, 6β‐, and 15β‐hydroxylation, which suggests that the 50‐kDa protein catalyzes the same pathways of testosterone oxidation as the 51‐kDa protein. However, this developmental increase in testosterone oxidation may have resulted from an activation of the 51‐kDa 3A protein. These results indicate that the two electrophoretically distinct proteins recognized by antibody against P450 3A1 are regulated in a similar but not identical manner, and suggest that the 51‐kDa 3A protein is the major microsomal enzyme responsible for catalyzing the 2β‐, 6β‐, and 15β‐hydroxylation of testosterone.
Biological action of lantadene C, a new hepatotoxicant from Lantana camara var. aculeata
Authors: Sharma Om P. , Vaid Jagdish , Pattabhi Vasantha , Bhutani Kamlesh K. 
Published: October 2006

AbstractLantadene C (22β‐2‐methylbutanoyloxy ‐3‐oxoolean‐12‐en‐28‐oic acid) isolated from the leaves of the hepatotoxic plant Lantana camara var. aculeata (Red) has been found to be identical with dihydrolan‐tadene A reported earlier. Molecular structure of lantadene C has been deduced from single crystal X‐ray diffraction analysis. It resembles lantadene A in the pentacyclic portion of the molecule but differs in the side chain region. Atom C‐34 is cis to C‐35 in lantadene C but is transin lantadene A. Semisynthetic lantadene C was prepared by catalytic hydrogenation of lantadene A. Lantadene C was obtained in two forms, I and II. Form I was crystalline while form II was amorphous. Unlike lantadene A, both form I and II of lantadene C elicited strong hepatotoxic response in guinea pigs associated with decrease in fecal output, feed intake, hepatomegaly, hepatic injury at the cellular and subcellular level, increase in plasma bilirubin, and acid phosphatase activity. All the clinical signs, hepatic lesions, and changes in blood plasma typified lantana toxicity. This is the first report on the hepatotoxicity of lantadene C. The interrelation of molecular structure and biological activity of lantadene A and C has been discussed.
The flavin‐containing monooxygenase in mouse lung: Evidence for expression of multiple forms
Authors: Venkatesh Krishnappa , Blake Bonnie , Levi Patricia E. , Hodgson Ernest 
Published: October 2006

AbstractThe flavin‐containing monooxygenase (FMO) was purified from mouse lung microsomes. On SDS‐PAGE, the purified enzyme separated as two bands, a major band of 58,000 daltons and a minor band of 59,000 daltons. Antibodies to mouse liver FMO cross‐reacted with both bands in the purified preparations, whereas antibodies to rabbit lung FMO cross‐reacted only with the major band. In microsomal preparations the major band was recognized by both antibodies, but neither antibody detected the minor band in microsomes. A cDNA encoding the pig liver FMO hybridized with mRNA isolated from mouse liver, kidney, and lung, whereas cDNA encoding the rabbit lung FMO hybridized only with mouse lung and kidney mRNA. Thermal stability studies showed that the FMO preparation purified from mouse lung consisted of a heat‐stable and a heat‐labile component. The heat‐labile component of lung FMO was inhibited competitively by imipramine, whereas the heat‐stable component was insensitive to the presence of imipramine. Immunoprecipitation of purified mouse lung FMO with anti‐rabbit lung FMO completely removed the protein band reactive to anti‐rabbit lung FMO while leaving reactivity to anti‐liver FMO. The catalytic and immunochemical differences seen between FMO from rabbit lung and mouse lung appear to result from the expression of at least two forms of FMO in the mouse lung, one similar to the rabbit pulmonary form and one similar to the major mouse liver form of FMO.
A chaperone‐mimetic effect of serum albumin on rhodanese
Authors: Jarabak Rebecca , Westley John , Dungan Joseph M. , Horowitz Paul 
Published: October 2006

AbstractReactivation of denatured rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) was found to be aided by the presence of serum albumin. Both the rate and the extent of reactivation of the urea‐denatured enzyme were optimal at low rhodanese and moderate serum albumin concentrations. Similarly, stabilization of the sulfurtransferase activity of rhodanese that had been partially unfolded at 40°C was aided by the presence of serum albumin. All the observations are in accord with a model in which enzyme that has been partially refolded from the urea‐denatured state or partially unfolded thermally interacts directly with serum albumin in a way that prevents rhodanese self‐association. Serum albumin thus acts as a molecular chaperone in these systems.
2,3,7,8‐tetrachlorodibenzo‐P‐dioxin induced alterations in protein phosphorylation in guinea pig adipose tissue
Authors: Enan Essam , Matsumura Fumio 
Published: October 2006

AbstractAn in situ (explant tissue culture) model has been developed to study the effect of 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD), hormones, and growth factors either alone or in combination. In our model system, the effect of TCDD on protein phosphorylation was greatly affected by the presence or the absence of externally added D‐glucose. In the presence of a physiologically relevant level of glucose (13.3 mM), TCDD clearly stimulated protein phosphorylation as in the case of in vivo data. However, in the absence of Dglucose TCDD clearly inhibited protein phosphorylation. On the other hand, TCDD reduced the glucose uptake activity in isolated adipose tissue either in the presence or absence of D‐glucose (13.3 mM). Therefore, the TCDD‐induced reduction of glucose transport does not appear to be related directly to the simultaneous rise in protein phosphorylation. For comparison, several agents which are known to affect protein phosphorylation were tested. These hormonal agents generally affected the TCDD‐untreated adipose tissues in the manner expected from their known actions, indicating that this in situ model is an adequate system to study their independent actions. The TCDD‐treated adipose tissue samples showed only mild or insignificant response to these hormonal stimuli. In terms of the changes in the pattern of protein phosphorylation activities, the action of TCDD appeared to resemble that of EGF and T3. Since under in situ conditions no agents such as EGF or T3 can be expected to be present, the observed TCDD‐induced changes are suggestive of the basic intracellular changes in cellular activities. The types of TCDD‐induced protein kinases appear to be protein tyrosine kinases and protein kinase C.
Effect of anti‐inflammatory agents on ricin‐induced macrophage toxicity
Authors: Naseem Syed M. , Pace Judith G. 
Published: October 2006

AbstractThe toxicity of ricin in susceptible cells is well characterized biochemically, but the pathophysiological implications of its toxicity and the immune response to ricin challenge in the lung are unknown. Incubating macrophage cell line with ricin (1 pM‐10 nM) for 4 hours markedly inhibited 3H‐leucine incorporation (acid insoluble) into protein (>95%, at 1 nM) without affecting the acid‐soluble radioactivity. In spite of increased uptake of total thymidine (141×13.5%) and total uridine (135×17.2%), DNA synthesis in ricin‐treated cells was progressively inhibited although RNA synthesis was not affected. Fluocinolone (an anti‐inflammatory glucocorticoid) pretreatment increased the ricin‐induced inhibition of protein synthesis. The synergistic effect of fluocinolone on ricin‐induced protein synthesis inhibition was due to an increased binding (167%, p < 0.01) and internalization (134×12%, p < 0.025) of ricin. Partial protection from ricin‐induced inhibition of protein synthesis by indomethacin (nonsteroidal, anti‐inflammatory agent) was due to decreased binding and internalization of ricin. These results show that macrophages are sensitive to ricin and that pharmacologically active drugs may regulate ricin's toxicity, perhaps by controlling synthesis and release of certain mediators of fast death.
Purification and properties of a diisopropyl‐fluorophosphatase from squid Todarodes pacificus steenstrup
Authors: Wang Fei , Xiao Meizhen , Mu Shaofeng 
Published: October 2006

AbstractA diisopropyl‐fluorophosphatase (DFPase) was purified from brain and ganglia of squid Todarodes pacificus steenstrup. The DFPase had a preference in hydrolysis toward diisopropylphosphorofluoridate (DFP). It also was able to hydrolyze O‐1,2,2‐trimethylpropyl methylphosphofluoridate (soman) and O‐isopropyl methylphosphonofluoridate (sarin) at nearly equal hydrolytic rates but only 1/10 that of DFP. The hydrolytic activity toward diethyl‐p‐nitrophenylphosphate (paraoxon) was very low compared with DFP, so man, and sarin. The DFPase was purified 330‐fold to a specific activity of 18,300 n mol/min/mg protein. Its molecular weight was 34,000 dalton determined by gel‐filtration chromatography. Mn2+ stimulation of the DFPase was not observed when DFP and soman were the substrates, but with sarin, the rate increased onefold in the presence of 1.0 mM of Mn2+. Ethylenediamine tetraacetic acid disodium (EDTA‐Na2) at 0.05 M inhibited the DFPase activity about 30%. It could be concluded that this DFPase belongs to the squid‐type DFPase.