ISSN:0887-2082    

DOI:10.1002/jbt.2570060302

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

年代:1991

数据来源: WILEY

摘要:

AbstractMicrocystin‐LR (MCYST‐LR), a cyclic peptide hepatotoxin, associates with high‐molecular‐weight, liver cytosolic components. Repetitive cycles of heat denaturation and pronase digestion released 80 ± 6% of the bound radiolabel from these components, parent toxin (22%), and two biotransformation products, with high‐performance liquid chromatography (HPLC) retention times of 6.7 (52%) and 5.6 (13%) min. Both parent and the biotransformed (6.7 min) toxin appeared to be covalently bound to a monomeric protein of molecular weight 40,000 (protein plus radiolabeled toxin). Binding and biotransformation reactions were time‐ and temperature‐dependent and did not require endogenous molecules<6,000 daltons. The binding appeared to be saturable with a maximum of 20 pmol MCYST‐LR bound per mg protein. The binding protein(s) and biotransformation activity were present in rat liver, brain, kidney, heart, lung, small intestine, large intestine, testes, skeletal muscle, and to a lesser extent, in fat. Okadaic acid, a specific protein phosphatase inhibitor, showed a concentration‐dependent inhibition of [3H]MCYST‐LR binding to hepatic cytosol. The molecular weight and organ distribution of the binding protein(s), and inhibition of binding by okadaic acid were consistent with one of the binding sites being the catalytic subunit of protein

ISSN:0887-2082    

DOI:10.1002/jbt.2570060303

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe activity patterns during development for acid phosphatase (Ac‐P), alkaline phosphatase (A1‐P), ß‐glucuronidase (ßG), and UDP‐glucuronyltransferase (UDPGT) have been determined in various tissues of the rat for corn oil and distilled water controls as well as in animals prenatally exposed to four fetotoxic chemicals. Postnatal assays were performed on both sexes separately. In control animals, tissue‐specific differences between male and female activity levels were found for UDPGT. In the liver of mature offspring, enzyme activity was greater in males than in females. Although no sex difference was observed in the intestine, the kidneys of females exhibited higher values than those of males. An original computer‐assisted methodology is presented, designed (a) to permit a mathematical description for the complex curves exhibited by these ontogeny profiles, and (b) to assess the statistical significance of chemical‐induced alterations in these complex developmental patterns, specifically, to target sensitive periods and subtle changes near the fetotoxic threshold. Oral administration (days 6–18 of gestation) of 3,3′,4,4′‐tetrachlorobiphenyl (4CB) to pregnant females resulted in an induction of liver UDPGT activity in offspring postnatally, and some alterations in the perinatal pattern of ßG in the same tissue. This treatment also produced differences in the intestinal patterns of Ac‐P and male UDPGT. No significant changes were observed in offspring exposed to diethylstilbestrol (DES). Treatment with zeranol (ZN) caused reductions in activity over the entire postnatal period for ßG in liver, brain, intestine, and kidney, for Al‐P in brain, and for Ac‐P in the intestine. Cadmium‐treated dams gave birth to offspring that exhibited slightly altered ontogenies only in intestine for UDPGT and AcP. The alterations in these developmental profiles indicate periods of increased sensitivity, and may be useful in directing more specific studies into the fetoto

ISSN:0887-2082    

DOI:10.1002/jbt.2570060304

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

年代:1991

数据来源: WILEY

摘要:

AbstractAnatoxin‐a(s) is a guanidine methyl phosphate ester (unprotonated molecular ion equals 252 daltons) isolated from the freshwater cyanobac‐terium (blue‐green alga)Anabaena flos‐aquaestrain NRC 525–17. Previous work has shown anatoxin‐a(s) to be a potent irreversible inhibitor of electric eel ace‐tylcholinesterase (EC 3.1.1.7, AChE). In the present study the interaction of anatoxin‐a(s) with AChE was investigated by protection studies and since similarities have been noted between anatoxin‐a(s) and the synthetic organophosphate anticholinesterases, the ability of reactivators to reactivate the inhibited enzyme was investigated. Treatments directed toward eliminating poisoning symptoms and in vivo protection from anatoxin‐a(s) poisonings were investigated using oxime reactivators and atropine or pretreatment with a carbamate and atropine. Anatoxin‐a(s) was shown to be an active site‐directed inhibitor of acetyl‐cholinesterase which is resistant to oxime reactivation due to the structure of its enzyme adduct. In vivo pretreatment with physostigmine and high concentrations of 2‐PAM were the only effective antagonists against a l

ISSN:0887-2082    

DOI:10.1002/jbt.2570060305

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe role of cytochrome P‐450 in the stimulation of lipid peroxidation by the nephrotoxic mycotoxin ochratoxin A has been investigated. Ochratoxin A was previously shown to markedly stimulate lipid peroxidation in a reconstituted system consisting of phospholipid vesicles, NADPH‐cytochrome P‐450 reductase, Fe3+, ethylenediaminetetra‐acetic acid (EDTA), and reduced nicotinamide adenine dinucleotide phosphate (NADPH). We now show that purified cytochrome P‐450IIB1 could effectively replace EDTA in stimulating lipid peroxidation suggesting that it could mediate the transfer of electrons from NADPH to Fe3+. Cobalt protoporphyrin is known to cause an extensive and long‐lasting depletion of hepatic cytochrome P‐450 in rats, and it has been used to evaluate the role of hepatic cytochrome P‐450 in xenobiotic metabolism and toxicity. We have observed that microsomes isolated from livers of cobalt protoporphyrin‐pretreated rats underwent ochratoxin A‐dependent lipid peroxidation much more slowly than control microsomes. Also, the level of ethane exhaled (an index of in vivo lipid peroxidation) on ochratoxin A administration was much lower in cobalt protoporphyrin‐pretreated rats than in control rats. Taken together, these results provide evidence for the stimulatory role of cytochrome P‐450 in ochratoxin A‐induced lipid peroxidation in a reconstituted system and strongly implicate its role in microsomal and in vivo ochratoxin A

ISSN:0887-2082    

DOI:10.1002/jbt.2570060306

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

年代:1991

数据来源: WILEY

摘要:

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

ISSN:0887-2082    

DOI:10.1002/jbt.2570060307

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effects of alterations in sulfur metabolism on hepatic and renal metallothionein and glutathione metabolism were studied in the adult rat using inhibition of two enzymes of these pathways, hepatic cystathionase and renal gamma‐glutamyl transpeptidase. Rats were fed a diet containing both methionine (0.66%) and cystine (0.20%) for 1 week before receiving three consecutive daily intraperitoneal injections of propargylglycine, a selective cystathionase inhibitor, at various doses (2.5–375 μmol/kg). When hepatic cystathionase was inhibited greater than 90% (≥50 μmol propargylglycine/kg), renal and hepatic metallothionein and hepatic glutathione were unaltered except at the highest dose. On the other hand, renal glutathione was increased twofold with a concomitant decrease in renal gamma‐glutamyl transpeptidase activity (50% of control). In another experiment, when renal gamma‐glutamyl transpeptidase was inhibited greater than 90% with three consecutive daily injections of acivicin, a selective gamma‐glutamyl transpeptidase inhibitor (10 mg/kg IP), renal glutathione content was unaltered while hepatic glutathione was decreased. Renal and hepatic metallothionein were not changed. Thus, the cysteine pools for metallothionein and glutathione appear unrelated under the present experimental conditions. In addition, following either propargylglycine or acivicin injections, renal and hepatic glutathione pools appear to be altered differently. These results suggest that renal glutathione may be preferentially maintained even when hepatic glutathione

ISSN:0887-2082    

DOI:10.1002/jbt.2570060308

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effects of three tetrachlorobiphenylols [2′,3′,4′,5′‐tetrachloro‐2‐biphenylol (1); 2′,3′,4′,5′‐tetrachloro‐4‐biphenylol (2); and 2′,3′,4′,5′‐tetrachloro‐3‐biphenylol (3)]; three monochlorobiphenylols [5‐chloro‐2‐biphenylol (5), 3‐chloro‐2‐biphenylol (6); and 2‐chloro‐4‐biphenylol (7)] and a tetrachlorobiphenyldiol [3,3′,5,5′‐tetrachloro‐4,4′‐biphenyldiol (4) on respiration, adenosine triphosphatase (ATPase)] activity, and swelling in isolated mouse liver mitochondria have been investigated. Tetrachlorobiphenylols (1–3) and the tetrachlorobiphenyldiol (4) inhibited state‐3 respiration in a concentration‐dependent manner with succinate as substrate (flavin adenine dinucleotide [FAD]‐linked) and the tetrachlorobiphenyldiol (4) caused a more pronounced inhibitory effect on state‐3 respiration than the other congeners. The monochlorobiphenylols5–7were less active as inhibitors of state‐3 mitochondrial respiration and significant effects were observed only at higher concentration (≥0.4 μM). However, in the presence of the nicotinamide adenine dinucleotide (NAD)‐linked substrates (glutamate plus malate), hydroxylated PCBs (1–7) significantly inhibited mitochondrial state‐3 respiration in a concentration‐dependent manner. Compounds 5, 6, and 7 uncoupled mitochondrial oxidative phosphorylation only in the presence of FAD‐linked substrate as evidenced by increased oxygen consumption during state‐4 respiratory transition, stimulating ATPase activity, releasing oligomycin‐inhibited respiration, and inducing mitochondrial swelling (5, 6, and7). Tetrachlorobiphenylols1, 2, and3had no effect on mitochondrial ATPase activity while the tetrachlorobiphenyldiol,4, decreased the enzyme activity. The possible in

ISSN:0887-2082    

DOI:10.1002/jbt.2570060309

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe effect on acetaminophen‐induced cytotoxicity of three calcium channel blocking agents‐diltiazem, verapamil and gallopamil‐was studied in primary cultures of rat hepatocytes and compared with the chelating agent EGTA. Using the measurement of cytosolic lactate dehydrogenase (LDH) as an index of cytotoxicity, it was demonstrated that a 1‐hr pretreatment with calcium channel blocking agents protected cells against acetaminophen cytotoxicity, but were less effective than EGTA. These data suggest that influx of extracellular Ca2+into the cells could have a role in the genesis of hepatocyte injury by acetam

ISSN:0887-2082    

DOI:10.1002/jbt.2570060310

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

年代:1991

数据来源: WILEY

ISSN:0887-2082    

DOI:10.1002/jbt.2570060301

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

年代:1991

数据来源: WILEY