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S H Safe

Publications and source records attributed to S H Safe.

At least 73 records · Page 4Linked to original sources
PubMed1986

Regulation of cytochrome P-450p by phenobarbital and phenobarbital-like inducers in adult rat hepatocytes in primary monolayer culture and in vivo.

Treatment of rats with phenobarbital increases the hepatic concentration of P-450p, a form of cytochrome P-450 believed to be controlled primarily by a mechanism that stereospecifically recognizes glucocorticoids like dexamethasone and anti-glucocorticoids like pregnenolone-16 alpha-carbonitrile [Schuetz, E.G., & Guzelian, P.S. (1984) J. Biol. Chem. 259, 2007]. To test the possibility that phenobarbital induces P-450p indirectly by increasing the availability of endogenous glucocorticoids in the liver, we added phenobarbital and phenobarbital-like inducers to primary monolayer cultures of adult rat hepatocytes incubated in serum-free medium without glucocorticoids and found stimulated de novo synthesis of P-450p measured as increased incorporation of [3H]leucine into immunoprecipitable P-450p protein. With some of the inducers, notably the organochlorine pesticides chlordane and trans-nonachlor, there was a greater accumulation of P-450p measured on quantitative immunoblots than could be accounted for by the increase in P-450p synthesis. "Pulse-chase" experiments confirmed that these compounds significantly lengthen the half-life of P-450p up to 60 h as compared to the values in control (11 h) or dexamethasone-treated (10 h) cultures. Treatment of rats with chlordane, trans-nonachlor, or other cyclodiene organochlorine pesticides confirmed that these agents increase the concentration of P-450p in liver microsomes analyzed on immunoblots of two-dimensional electrophoretic gels. The time courses of induction in trans-nonachlor-treated rats of P-450p protein and of P-450PB proteins induced by phenobarbital were similar as were the amounts of P-450PB mRNA and P-450p mRNA measured by hybridization to cloned cDNA probes. However, analysis of structure-activity relationships among polychlorinated biphenyls revealed that isomers with two ortho chlorinated positions maximally induced P-450PB whereas isomers with three and four ortho chlorines maximally induced P-450p in rats and in hepatocyte culture, respectively. We conclude that P-450p is induced by the phenobarbital class of inducers through direct contact with the hepatocytes involving decreased degradation of the protein and stimulation of its synthesis in a manner similar but not identical with that of P-450PB.

Animals↗
PubMed1986

Monoclonal antibodies to chlorinated dibenzo-p-dioxins.

A thyroglobulin conjugate of dioxin (thyroglobulin-2 adipamide, 3,7,8-trichlorodibenzo-p-dioxin) (TG-TCDD) was used to immunize BALB/c mice. Hybridomas were produced by cell fusion between immune spleen cells and mouse myelomas SP2/0, P3, or NS1. To screen the thousands of resultant cultures for production of monoclonal antibodies (MoAb), a rapid, solid-phase radioimmunoassay for antibody to dioxins was developed. This procedure involved attaching bovine serum albumin coupled with trichlorodibenzo-p-dioxin (BSA-TCDD) to polystyrene plates to be used as a solid-phase target antigen for reaction with MoAb. Fourteen hybridomas were identified that produced MoAb reacting with BSa-TCDD but not with BSA alone. Antibodies were tested for binding to BSA-aniline to eliminate those with limited binding specificity. Initial studies indicated that most MoAbs bound BSA-aniline as well as BSA-TCDD. More detailed analyses indicated that while most MoAbs showed some reaction with BSA-aniline, two showed preferential binding to BSA-TCDD of more than 200-fold whereas rabbit antisera demonstrated only a 5-fold discrimination. MoAb 391-1B was purified from mouse ascites fluid and after radioiodination, was tested for direct binding to BSA-TCDD or BSA-aniline. 125I-MoAb 391-1B showed no significant binding to BSA-aniline while demonstrating high binding to BSA-TCDD (Ka = 4.5 X 10(8) liters/mol).

Amides↗
PubMed1986

Influences of different polychlorinated biphenyls on cytocidal, mitoinhibitory, and nodule-selecting activities of N-2-fluorenylacetamide in rat liver.

The influences of different polychlorinated biphenyl (PCB) isomers and congeners on distinct hepatotoxic responses to the hepatocarcinogen N-2-fluorenylacetamide [(2-FAA) CAS: 53-96-3] were examined in F344 rats. Cytocidal toxicity of 2-FAA (25-400 microM), determined by lactate dehydrogenase release during 20 hours in primary monolayer cultures of isolated rat hepatocytes, was reduced by in vivo pretreatment with either phenobarbitone [(PB) CAS: 50-06-6] or 2,2',4,4',5,5'-hexachlorobiphenyl (HCBP), a PB-type PCB inducer. However, cytocidal toxicity of 2-FAA was substantially potentiated by either 3-methylcholanthrene [(MCA) CAS: 56-49-5] or 3,3',4,4'-tetrachlorobiphenyl [(TCBP) CAS: 32598-13-3], an MCA-type PCB. In the same cell culture assays, all four pretreatments similarly reduced cytocidal toxicity of N-hydroxy-N-2-fluorenylacetamide (0.32-32 microM; CAS: 53-95-2). By comparison, pretreatments with either the PB-type or MCA-type PCB's (50-200 mumol/kg) diminished mitoinhibitory toxicity of 2-FAA in vivo, as measured by hepatic regenerative growth and hepatocyte labeling indices 7 days after partial hepatectomy (PH) in rats given 3 consecutive daily doses of 2-FAA (20/mg/kg/day) before PH. This regimen of 2-FAA and PH promoted rapid selective growth of gamma-glutamyltranspeptidase-positive (gamma-GT+) nodules at 2 and 4 weeks after PH in rats previously given an initiating hepatocarcinogen, diethylnitrosamine [(DENA) CAS: 55-18-5]. However, various PCB's, including 2,2',4,4',5,5'-HCBP, 3,3',4,4'-TCBP, 2,2',4,4'-TCBP, 2,2',5,5'-TCBP, and the commercial mixture Aroclor 1254, each given as a single dose of 50 mumol/kg by gavage 10 days after DENA and 7 days before 2-FAA, all reduced the size of 2-FAA-selected gamma-GT+ nodules during the 4-week period after PH. These results indicate that, in spite of predictable inducer-specific opposite influences of different types of PCB's on cytocidal toxicity of 2-FAA, all PCB's similarly reduce nodule selection by 2-FAA in initiated livers. Reduced growth of 2-FAA-selected nodules correlated with the consistent ability of all PCB's to enhance regeneration of liver mass after 2-FAA and PH.

2-Acetylaminofluorene↗
PubMed1985

Metabolism of aflatoxin B1 by rat hepatic microsomes induced by polyhalogenated biphenyl congeners.

The metabolism of aflatoxin B1 to aflatoxins M1 and Q1 by rat liver microsomes from animals pretreated with polychlorinated or polybrominated biphenyl congeners depended on the structure of the halogenated biphenyl inducers. Microsomes from rats treated with phenobarbital (PB) or halogenated biphenyls that exhibit PB-type activity preferentially enhanced the conversion of aflatoxin B1 to aflatoxin Q1. In contrast, microsomes from rats treated with 3-methylcholanthrene (MC) or halogenated biphenyls that exhibit MC-type induction activity increased the metabolism of aflatoxin B1 to aflatoxin M1. The coadministration of PB and MC produced microsomes that exhibited both types of induction activity (mixed type) in catalyzing the oxidative metabolism of diverse xenobiotic agents. However, PB-plus-MC-induced hepatic microsomes from immature male Wistar rats preferentially increased the metabolism of aflatoxin B1 to aflatoxin M1 but did not enhance the conversion of aflatoxin B1 to aflatoxin Q1. Comparable results were observed with microsomes from rats pretreated with halogenated biphenyls classified as mixed-type inducers; moreover, in some cases there was a significant decrease in the conversion of aflatoxin B1 to aflatoxin Q1 (compared with that of controls treated with corn oil).

Aflatoxins↗
PubMed1985

Influence of cell proliferation on initiating activity of pure polychlorinated biphenyls and complex mixtures in resistant hepatocyte in vivo assays for carcinogenicity.

The abilities of various pure polychlorinated biphenyls (PCB) and complex mixtures to generate resistant gamma-glutamyltransferase (GGT)-positive hepatocellular nodules was evaluated in F344 rats in which hepatocytes were proliferating. The PCB examined were 2,2',4,4',5,5'-hexachlorobiphenyl (CAS: 35065-27-1), 2,2',4,4'-tetrachlorobiphenyl, 2,2',5,5'-tetrachlorobiphenyl, Aroclor 1254 (CAS: 11097-69-1), and a prepared mixture of pure PCB isomers and congeners similar to those found in human breast milk. The PCB were administered either to male and female suckling rats (weekly for 3 wk) during liver growth or to adult male rats (150-160 g body wt) previously subjected to two-thirds partial hepatectomy (PH). Rats were subsequently given a selection regimen consisting of 3 daily doses (20 mg/kg) of 2-acetylamino-fluorene (2-FAA; CAS: 53-96-3) followed by either PH or necrotizing carbon tetrachloride (CAS: 56-23-5) in adult rats that previously underwent PH. None of the PCB exposures generated GGT-positive nodules after selection, whereas known initiators such as diethylnitrosamine (CAS: 55-18-5), 3-methylcholanthrene (CAS: 56-49-5), benzo[a]pyrene (CAS: 50-32-8), and 2-FAA were active initiators of nodules in suckling or hepatectomized rats. These findings indicate that short-term exposures to these PCB during liver cell proliferation do not show initiating action in an in vivo assay that detects both hepatic and nonhepatic initiating carcinogens.

Animals↗
PubMed1984

Comparative influences of different PB-type and 3-MC-type polychlorinated biphenyl-induced phenotypes on cytocidal hepatotoxicity of bromobenzene and acetaminophen.

The influences of in vivo treatment with two pure PCB congeners, 2,2',4,4',5,5'-hexachlorobiphenyl (HCBP) and 3,3',4,4'-tetrachlorobiphenyl (TCBP), on the lethal cytotoxicity of bromobenzene and acetaminophen were examined in short-term primary cultures of isolated rat hepatocytes. Lethal injury was measured by release of lactate dehydrogenase (LDH) into culture medium after 20 hr exposure to the hepatotoxins. The HCBP, a PB-type inducer of cytochrome P-450, resembled phenobarbitone (PB) in its ability to increase susceptibility of hepatocytes to bromobenzene (0.5 to 1.6 mM) and acetaminophen (1 to 16 mM). This induced sensitivity was consistently inhibited by SKF-525-A (10 microM) but not alpha-naphthoflavone (ANF, 10 microM) in culture. The 3,3',4,4'-TCPB, a 3-MC-type inducer of cytochrome P-450, resembled 3-methylcholanthrene (3-MC) in its inability to induce susceptibility to bromobenzene. TCBP and 3-MC each increased (20- to 30-fold) cytotoxicity of acetaminophen by a mechanism substantially inhibitable by ANF but not SKF-525-A. These results demonstrate that categorizing pure PCB isomers and congeners into groups according to their different induction capabilities is predictive for their ability to modulate acute hepatocellular necrosis by bromobenzene and acetaminophen.

Acetaminophen↗
PubMed1984

PCBs and PBBs: biologic and toxic effects on C57BL/6J and DBA/2J inbred mice.

Treatment of genetically inbred "responsive" C57BL/6J and "non-responsive" DBA/2J mice with Aroclor 1254 or fireMaster BP-6 resulted in the induction of hepatic microsomal benzo[a]pyrene hydroxylase only in the former mouse strain and aminopyrine N-demethylase in both strains of mice. In contrast, 3,3',4,4',5-pentachlorobiphenyl and 3,3',4,4'-tetrabromobiphenyl, induced benzo[a]pyrene hydroxylase in both C57BL/6J and DBA/2J but did not enhance aminopyrine N-demethylase in either strain of mouse. Both these coplanar halogenated biphenyls also caused thymic atrophy in the responsive and non-responsive mice and their effects resembled those of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Treatment of the inbred mice with several mono-ortho substituted analogs of the coplanar halogenated biphenyls, including 2,3,3',4,4'-pentachloro-, 2,3',4,4',5-pentabromo-, 2,3,3',4,4',5-hexachloro- and 3',4'-dibromo-2,3,4,5-tetrachlorobiphenyl, gave hepatic enzyme-induction results similar to those observed for the commercial halogenated biphenyls. At dose levels of 1500 mumol/kg, most of these compounds caused thymic atrophy in C57BL/6J mice but not in DBA/2J mice. The structure-activity correlations in the mice complement similar studies with the halogenated biphenyls in rats and support the proposed receptor-mediated mechanism for the toxic halogenated aromatics.

Aminopyrine N-Demethylase↗
PubMed1984

Influences of various xenobiotic inducers on cytocidal toxicity of lasiocarpine and senecionine in primary cultures of rat hepatocytes.

The influences of in vivo pretreatment with phenobarbitone (PB), 3-methylcholanthrene (3-MC), 2,2',4,4',5,5'-hexachlorobiphenyl (HCBP), and 3,3',4,4'-tetrachlorobiphenyl (TCBP) on cytocidal hepatotoxicity of two pyrrolizidine alkaloids, lasiocarpine (LC) and senecionine (SC), were compared in short-term primary cultures of rat hepatocytes. Toxicity was measured by release of lactate dehydrogenase (LDH) into culture medium at 24 h. LC was slightly more toxic to control hepatocytes than SC in the graded response range of 10-160 microM. PB and HCBP (a PB-type polychlorobiphenyl inducer) similarly potentiated toxicity of SC, and each diminished the degree to which cell killing by LC and SC was inhibited by SKF-525-A. By comparison, 3-MC and TCBP (a 3-MC-type PCB inducer) each diminished toxicity of SC but had little effect on toxicity of LC. Alpha-naphthoflavone (ANF) potentiated toxicity of both LC and SC in hepatocytes induced by 3-MC or TCBP but had little effect on responses of hepatocytes induced by either PB or HDBP. These results indicate that xenobiotics that induce similar patterns of cytochrome P-450 isozymes have qualitatively similar modulating influences on cytocidal hepatotoxicity of pyrrolizidine alkaloids in primary cultures. However, the observed modulating effects could not be explained solely on the basis of altered activation rates by the cytochrome P-450 species known to be induced by the various xenobiotics.

Animals↗
PubMed1984

Aflatoxin B1 metabolism in the rat: polyhalogenated biphenyl enhanced conversion to aflatoxin M1.

The effects of polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs) on the formation in vitro of aflatoxin Q1 and aflatoxin M1 from aflatoxin B1 by rat-liver microsomes were investigated. AFB1 metabolism by hepatic microsomes from PBB- and PCB-treated rats resulted in 16- and 30-fold increases, respectively, in levels of aflatoxin M1. The enhanced formation of aflatoxin M1 did not correlate with PBB and PCB stimulation of benzo[a]pyrene hydroxylase (AHH) activity. Studies in vivo clearly demonstrated enhanced secretion of aflatoxin M1 by female lactating rats with prior exposure to PCBs. PCB pretreatment enhanced the activity of mammary as well as hepatic tissue microsomal preparations in converting aflatoxin B1 to aflatoxin M1. Our findings indicate that PCB exposure increases the production of aflatoxin M1 in vitro and also increases the levels of aflatoxin M1 released into the milk.

Aflatoxin B1↗
PubMed1983

Induction of rat hepatic microsomal cytochrome P-450 by 2,3',4,4',5,5'-hexachlorobiphenyl.

The following evidence suggests that 2,3',4,4',5,5'-hexachlorobiphenyl resembles isosafrole as an inducer of hepatic microsomal cytochrome P-450d in the immature male Wistar rat. First, the major hepatic microsomal polypeptide (Mr = 52,000), intensified after treatment of rats with 2,3',4,4',5,5'-hexachlorobiphenyl, comigrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with cytochrome P-450d (i.e. the major isosafrole-inducible polypeptide) but had an electrophoretic mobility intermediate between cytochrome P-450b (Mr approximately equal to 51,500) and cytochrome P-450c (Mr = 56,000) (i.e. the major phenobarbital- and 3-methylcholanthrene-inducible polypeptides respectively). Second, when pairs of various xenobiotics were coadministered to rats at doses effecting maximal induction of hepatic microsomal cytochrome P-450, the inductive effects of 2,3',4,4',5,5'-hexachlorobiphenyl were additive with those of phenobarbital, 3-methylcholanthrene and pregnenolone-16 alpha-carbonitrile but not with those of isosafrole. The inductive effects of phenobarbital, 3-methylcholanthrene, pregnenolone-16 alpha-carbonitrile and isosafrole were all expressed additively with each other. Third, in contrast to phenobarbital and pregnenolone-16 alpha-carbonitrile treatment, treatment of rats with 2,3',4,4',5,5'-hexachlorobiphenyl, isosafrole or 3-methylcholanthrene failed to increase markedly the proportion of total cytochrome P-450 capable of forming a 446 nm-absorbing complex with metyrapone. Fourth, the in vitro metabolism of isosafrole, catalyzed by hepatic microsomes from rats treated with 2,3',4,4',5,5'-hexachlorobiphenyl, isosafrole or 3-methylcholanthrene, produced complexes between ferrous cytochrome P-450 and a methylenedioxyphenyl metabolite, the spectra of which were between 400 and 500 nm and were similar to each other but which were readily distinguishable from the spectra of the product adducts formed during the metabolism of isosafrole by hepatic microsomes from rats treated with corn oil (control), phenobarbital, or pregnenolone-16 alpha-carbonitrile.

Animals↗
PubMed1983

Differential time course of induction of rat liver microsomal cytochrome P-450 isozymes and epoxide hydrolase by Aroclor 1254.

The time course of induction of rat liver microsomal cytochromes P-450a, P-450b + P-450e, P-450c, and P-450d and epoxide hydrolase has been determined in immature male rats administered a single large dose [1500 mumol (500 mg)/kg body wt] of the polychlorinated biphenyl mixture Aroclor 1254. Differential regulation of these xenobiotic-metabolizing enzymes was indicated by their characteristic patterns of induction. The rate of induction of cytochrome P-450a and epoxide hydrolase was relatively slow, and steady-state levels of these enzymes were maintained from approximately Days 9 to 15 after Aroclor 1254 treatment. In contrast, cytochrome P-450c was maximally induced 2 days after Aroclor 1254 treatment and remained at a constant level through Day 15. Steady-state levels of cytochrome P-450d, beginning 1 week after Aroclor 1254 treatment, were preceded by a fairly rapid rate of induction and possibly by a small decline from maximal levels observed around Days 4 to 5. Like those of the other cytochrome P-450 isozymes and epoxide hydrolase, the levels of cytochromes P-450b + P-450e were constant from Day 9 to 15 after Aroclor 1254 treatment. However, an unexpected but reproducible decline (approximately 25%) in total cytochrome P-450 content observed between Days 4 and 9 after Aroclor 1254 treatment principally reflected a dramatic and totally unanticipated decrease (approximately 45%) in the level of cytochromes P-450b + P-450e. This transient decline in the level of cytochromes P-450b + P-450e was not due to an unusual effect of a mixture of polychlorinated biphenyls, since identical results were obtained with two individual congeners, namely 2,3,4,5,4'-penta- and 2,3,4,5,3',4'-hexachlorobiphenyl, that induced the same isozymes as Aroclor 1254. In contrast, when rats were treated with 2,4,5,2',4',5'-hexachlorobiphenyl, which induces cytochromes P-450a and P-450b + P-450e and epoxide hydrolase but not cytochromes P-450c or P-450d, maximal levels of cytochromes P-450b + P-450e were attained on Day 4 and no decrease was observed over the next 11 days. These results suggest that there may be an interaction in the regulation of induction of certain individual cytochrome P-450 isozymes.

Animals↗
PubMed1983

Toxicity of 3,3',4,4'- and 2,2',5,5'-tetrabromobiphenyl: correlation of activity with aryl hydrocarbon hydroxylase induction and lack of protection by antioxidants.

3,3',4,4'-Tetrabromobiphenyl is a minor component of commercial polybrominated biphenyl (PBB) mixture fireMaster BP-6 and is a potent inducer of aryl hydrocarbon hydroxylase (AHH). A single ip dose of 3,3',4,4'-tetrabromobiphenyl (150 mumol/kg) caused significant reduction in the growth rate in the immature male Wistar rat, as well as pale enlarged livers and marked reduction in thymus size. Under light microscopy, hepatocytes were enlarged and vacuolated. The vacuoles, which were most prominent in the midzonal region of the lobule, corresponded to fat droplets in oil-red-O-stained sections. The thymus, especially the cortex, was markedly depleted of lymphocytes. Neither the reduced growth, altered organ weights nor the histopathology was reversed for the duration of the study by the coadministration of the antioxidants butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT), or vitamin E. Vitamin E did, however counter the negative effect of 3,3',4,4'-tetrabromobiphenyl on growth during the first 5 d of the study. 2,2',5,5'-Tetrabromobiphenyl, also a minor component of fireMaster BP-6, is a weak phenobarbital-type inducer of cytochrome P-450. When administered at the same dose, 2,2',5,5'-tetrabromobiphenyl did not elicit any observed toxic effects. These data confirm the correlation between AHH induction and toxicity for these PBBs and suggest that 3,3',4,4'-tetrabromobiphenyl may significantly contribute to the toxicity of fireMaster BP-6. Although there is evidence that polychlorinated biphenyls, and perhaps 2,3,7,8-tetrachlorodibenzo-p-dioxin, exert certain toxic effects via a lipid peroxidation mechanism, the toxic changes measured during this study were not reversed by the administration of the antioxidants.

Animals↗
PubMed1980

Fragmentation pathways in electron impact mass spectra of methoxyhalobiphenyls.

The electron impact mass spectra of various methoxyhalobiphenyls have been reinvestigated. Previous findings, concerning the effect of the methoxy group upon the main fragmentation routes, have been confirmed and extended. In addition, studies of unimolecular and collision induced fragmentation of ions, using linked scan techniques, have been made. Such an approach permits the identification of substances with a minimal chromatographic separation prior to mass spectrometry. It has also led to some clarification of the fragmentation pathways leading to the observed cracking patterns.

Biphenyl Compounds↗
PubMed1978

Enhanced virus replication in mammalian cells exposed to commercial emulsifiers.

Mammalian cell cultures were used to show that a variety of commercial emulsifiers are capable of enhancing the sensitivity of these cells to infection with several viruses. Some emulsifiers were not active as enhancers, and those viruses that responded to the enhancing emulsifiers were single-stranded ribonucldic acid viruses. The double-stranded viruses that were tested were nonresponders.

Cell Line↗
PubMed1977

Sterol content and polyene antibiotic resistance in isolates of Candida krusei, Candida parakrusei, and Candida tropicalis.

Three isolates, one from each species of Candida krusei, C. parakrusei, and C. tropicalis, obtained from infected patients, were more tolerant of significantly higher concentrations of polyene antibiotics than the corresponding reference wild types. The resistant strains isolated had the same sterols as their wild-type counterparts but in lower concentrations.

Amphotericin B↗