摘要:

AbstractIn vitroincubation of rat liver micro‐somes with [14C]‐furan in the presence of NADPH resulted in the covalent incorporation of furan‐derived radioactivity in microsomal protein. Compared to microsomes from untreated rats a two‐ to threefold increase in binding was observed with microsomes from phenobarbital‐treated rats and a four‐ to five‐fold increase was observed with microsomes from rats pretreated with imidazole or pyrazole. Covalent binding was reduced with microsomes from rats pretreated with β‐naphthoflavone. Chemicals containing an amine group (semicarbazide), those in which the amine group is blocked but have a free thiol group (N‐acetylcysteine), and those which have both an amine and a thiol group (glutathione) effectively blocked binding of [14C]‐furan to microsomal protein. A decrease in cytochrome P‐450 (P‐450) content and decreases in the activities of P‐450‐dependent aniline hydroxylase, 7‐ethoxycoumarin‐O‐deethylase (BCD), and 7‐ethoxyresorufin‐O‐deethylase (ERD) was observed 24 hours after a single oral administration of 8 or 25 mg/kg of furan, suggesting that the reactive intermediate formed during P‐450 catalyzed metabolism could be binding with nucleophilic groups within the P‐450.In vitrostudies indicated a significant decrease in the activity of aniline hydroxylase in pyrazole microsomes and BCD in phenobarbital microsomes without any significant change in the CO‐binding spectrum of P‐450 or in the total microsomal heme content, suggesting that furan inhibits the P‐450s induced by PB and pyrazole. An almost equal distribution of furan‐derived radioactivity in the heme and protein fractions of the CO‐binding particles afterIn vitrotreatment of microsomes with furan suggests binding of furan metabolites with heme and apoprotein of P‐450, and, probably, due to this inte

ISSN:0887-2082    

DOI:10.1002/jbt.2570080103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractInduction of P450HE1 by pyridine was compared with that by ethanol, and the resulting potentiation of the pneumotoxicity and hepato‐toxicity following carbon tetrachloride inhalation by pyridine was examined. Rats were treated with ethanol as either a 10% solution in the drinking water or as a daily bolus (3 ml/kg, ip) dose for 7 days or one bolus dose of pyridine (200 mg/kg, ip) and compared for P450IIE1 apoprotein content by immunoblot analysis. Ethanol in the drinking water and pyridine elevated both hepatic and pulmonary P450IIE1 apoprotein content, but bolus dose ethanol did not. The induction was greatest in the pyridine group. In the interaction study, rats were treated with pyridine (200 mg/kg, ip) and 12 hours later were exposed to CC14(8000 ppm for 3 hours). Pulmonary injury and hepatic damage were assessed 24 hours later by bronchoalveolar lavage fluid (BALF) analysis [γ‐glutamyl transpeptidase (GGT), lactate dehydrogenase (LDH), and total protein] and serum sorbitol dehydrogenase (SDH) activity, respectively. Pyridine alone had no effect on BALF or SDH but enhanced GGT and LDH release into the BALF and SDH release into the serum when compared with CC14exposure alone. Evaluation of the liver at the light microscopic level revealed characteristic CCl4‐induced centrilobular necrosis which was potentiated by pyridine. No changes were observed in the lung by light microscopic evaluation. Pyridine induced pulmonary and hepatic microsomal apoprotein levels of cytochrome P450IIE1 two‐ and 2‐ to sixfold, respectively. Exposure to CC14decreased hepatic but not pulmonary P450IIE1 levels. Induction of cytochrome P450IIE1 by pyridine increases the bioactivation of CC14in both the liver and lung, leading to enhance

ISSN:0887-2082    

DOI:10.1002/jbt.2570080104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractFor organophosphatesor phosphoratesto initiate delayed neuropathy two steps are necessary: (1) progressive covalent reaction with neuropathy target esterase (NTE) to produce a form of inhibited NTE which can be reactivated by incubation with aqueous potassium fluoride (KF) and (2) progressive “aging” of inhibited NTE to a form which can no longer be reactivated by KF. However, it has been shown recently that certain N‐unsubstituted organophosphoro‐monoamidates(analogues of methamidophos) cause delayed neuropathy even though the inhibited NTE appeared not to have aged (Johnsonet al.(1991).Arch. Tox‐icol., 65, 618–624). In order to study the generality of this phenomenon, we have examined some N‐substituted compounds. We reportIn vitrostudies of inhibition and reactivation and aging of both NTE and acetylcholinesterase (AChE) prior to tox‐icological tests. All the compounds studied were less inhibitory to both NTE and AChE in concentrated rather than in dilute suspensions of EDTA‐washed brain particles without added cofactors. There was an apparent disposal of up to 100 üumoles of test compound by particles from 95 mg hen brain, which is far greater than can be explained by covalent binding. The activity is distinct from calcium‐dependent “A” esterase. Several N‐alkyl phosphoromonoamidates were found to be potent and selective inhibitors of NTE: second‐order rate constant for O‐n‐pentyl N‐benzylphosphoramido‐fluoridate (Cmpd 6) = 5.6×107M−1min−1at 37°, which is about l00% higher than for acetylcholinesterase (AChE). Inhibited NTE and AChE from several chiral phosphoromono‐amidates did not reactivate spontaneously (21 hours at 37°). Virtually 100% reactivation by KF of AChE inhibited by phosphoromonoamidates was achieved at all times tested. Acetylcholinesterase inhibited by 2,5‐dichlorophenyl N,N′‐di‐n‐butylphosphorodiamidatewas 42–56% reactivated by incubation with KF (192 mM in pH 5.2 buffer for 30 minutes at 37°rpar;. We believe this is the first report of reactivation of any enzyme after inhibition by a phosphorodi'amidate. For NTE inhibited by tabun (O‐ethyl N‐dimethylphosphoroamidocyanidate), virtually complete and rapid aging (t1/2= 5.5–8.4 minutes) was observed. Consistent but only partial reactivation by KF was achieved 2 or more hours after inhibition of NTE by Cmpd 6 or by its 2,6‐difluoro‐an‐alogue (Cmpd 7). However, a small but significant aging (approximately 15–20% loss of reactivatability) was measured soon after a 1 minute inhibition by Cmpd 7, but no further change occurred in 21 hours. We conclude that, of the two chiral forms of NTE obtainable from chiral N‐substituted phosphoromonoamidates, one form can and does age rapidly while the enantiomeric f

ISSN:0887-2082    

DOI:10.1002/jbt.2570080105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effects of transition metals on nonenzymatic and ceruloplasmin catalyzed epinephrine oxidation were investigated by studying rates of epinephrine oxidation in purified buffers and in the presence of metal chelating agents. We found that epinephrine does not “autoxidize” in sodium chloride solutions prepared with deionized water that was further purified by chromatography over Chelex 100 resin prior to use. Epinephrine was oxidized rapidly in sodium chloride prepared with tap water (1.20±0.12 nmoles/min) or in deionized water (0.40±0.80 nmoles/min), but this oxidation was prevented by the addition of Desferal, a potent metal chelating agent. Epinephrine oxidation was enhanced upon the addition of ceruloplasmin, and this oxidation rate could be slowed, but not eliminated, by the addition of Desferal. If epinephrine solutions were preincubated for 72 hours with Desferal prior to ceruloplasmin addition, however, no oxidation was observed. Epinephrine was shown to form colored complexes with both iron and copper at pH 7.0. The Fe(III)‐epinephrine complex was much more stable than was the Cu(II)‐epinephrine complex. Oxygen consumption studies of ceruloplasmin catalyzed epinephrine oxidation showed that copper was a better promoter of epinephrine oxidation than was iron, suggesting that ceruloplasmin‐catalyzed epinephrine oxidation results from adventitious copper bound to the purified enzyme. In light of these results, the physiological relevance of ceruloplasmin catalyzed oxidation of biogenic amines m

ISSN:0887-2082    

DOI:10.1002/jbt.2570080106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

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 s

ISSN:0887-2082    

DOI:10.1002/jbt.2570080107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe relationship between the covalent binding, uptake, and toxicity produced by S‐(1,2‐dichlorovinyl)‐L‐cysteine (DCVC) and S‐(1,1,2,2‐tetrafluoroethyl)‐L‐cysteine (TFEC) was investigated in suspensions of rabbit renal proximal tubules (RPT). The DCVC and TFEC at concentrations of 25 μM produced a time‐dependent (1–6 hours) loss of RPT viability. The TFEC was bio‐transformed rapidly by β‐lyase to a reactive metabolite which bound covalently to tubular protein. Approximately 63% of the TFEC‐equivalents inside the cell were bound to protein. Covalent binding of TFEC‐equivalents was associated with a 30% decrease in tubular basal and state 3 respiration, a sevenfold increase in lipid peroxidation, and, ultimately, cell death. The DCVC was biotransformed rapidly to a reactive metabolite which bound covalently to tubular protein. Approximately 90% of the DCVC‐equivalents inside the cell were bound covalently to tubular protein. Following exposure to 25 μM DCVC, the binding of DCVC‐equivalents was associated with a 17‐fold increase in lipid peroxidation but, in contrast to TFEC, had no effect on tubular respiration. However, exposure of RPT to 100 μM DCVC resulted in a ninefold increase in the binding of DCVC‐ equivalents and a 30% decrease in tubular state 3 respiration. The β‐lyase inhibitor aminooxyacetic acid (AOAA) blocked the covalent binding, mitochondrial dysfunction, lipid peroxidation, and cell death produced by TFEC. The AOAA decreased the covalent binding and the lipid peroxidation produced by DCVC by approximately 60–70% but had no effect on cell death. These results suggest that mitochondria! bioactivation of TFEC by β‐lyase is critical for TFEC‐induced mitochondrial dysfunction and the resulting cell death. These results also suggest that cytosolic bioactivation and binding, but not mitochondrial bioactivation and dysfunction, are important in the toxicity produced by DCVC to rabbit RPT. The lack of protection against DCVC toxicity by AOAA may be related to incomplete inhibition of DCVC metabolism or bio

ISSN:0887-2082    

DOI:10.1002/jbt.2570080108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0887-2082    

DOI:10.1002/jbt.2570080102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY