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E Hodgson

Publications and source records attributed to E Hodgson.

At least 37 records · Page 2Linked to original sources
PubMed1998

Common mechanism of toxicity: a case study of organophosphorus pesticides.

The Food Quality Protection Act of 1996 (FQPA) requires the EPA to consider "available information concerning the cumulative effects of such residues and other substances that have a common mechanism of toxicity ... in establishing, modifying, leaving in effect, or revoking a tolerance for a pesticide chemical residue." This directive raises a number of scientific questions to be answered before the FQPA can be implemented. Among these questions is: What constitutes a common mechanism of toxicity? The ILSI Risk Science Institute (RSI) convened a group of experts to examine this and other scientific questions using the organophosphorus (OP) pesticides as the case study. OP pesticides share some characteristics attributed to compounds that act by a common mechanism, but produce a variety of clinical signs of toxicity not identical for all OP pesticides. The Working Group generated a testable hypothesis, anticholinesterase OP pesticides act by a common mechanism of toxicity, and generated alternative hypotheses that, if true, would cause rejection of the initial hypothesis and provide criteria for subgrouping OP compounds. Some of the alternative hypotheses were rejected outright and the rest were not supported by adequate data. The Working Group concluded that OP pesticides act by a common mechanism of toxicity if they inhibit acetylcholinesterase by phosphorylation and elicit any spectrum of cholinergic effects. An approach similar to that developed for OP pesticides could be used to determine if other classes or groups of pesticides that share structural and toxicological characteristics act by a common mechanism of toxicity or by distinct mechanisms.

Animals↗
PubMed1998

Physiological factors affecting protein expression of flavin-containing monooxygenases 1, 3 and 5.

1. The mouse and rat exhibit substantial differences in the gender expression of flavin-containing monooxygenase (FMO) forms. Hepatic FMO1 is gender-dependent in both species, selective to the male in rat, female in mouse. Human FMO1 is nearly undetectable. FMO3 in mouse is gender-specific to the female, but gender-independent in rat and man. FMO5 is gender-independent for mouse, rat and man. 2. Gender differences in substrate metabolism do not reflect overall FMO or isoform differences. Methimazole, imipramine and thiobenzamide are much better substrates for FMO1 than for FMO3 or FMO5. 3. Activities of microsomal samples toward these substrates reflect the relative abundance of FMO1. Hepatic samples show a 3-fold greater activity toward methimazole in the female mouse and male rat. Human microsomal samples show minimal activity. 4. Developmentally, FMO1 and FMO5 are expressed in foetuses as early as gestation days 15 and 17 and equally between genders until puberty. FMO3 is not found until 2 weeks post-partum and is found equally in the male and female until 6 weeks post-partum when it becomes undetectable in the male. 5. An event takes place after birth but before puberty that confers the ability to produce FMO3. The developmental pattern observed for mouse FMO3 is similar to human FMO3.

Adult↗
PubMed1997

Molecular cloning, sequencing, and expression in Escherichia coli of mouse flavin-containing monooxygenase 3 (FMO3): comparison with the human isoform.

The sequence of mouse flavin-containing monooxygenase 3 (FMO3) was obtained from several clones isolated from a mouse liver cDNA library. The nucleotide sequence of mouse FMO3 was 2020 bases in length containing 37 bases in the 5' flanking region, 1602 in the coding region, and 381 in the 3' flanking region. The derived protein sequence consisted of 534 amino acids including the putative flavin adenine dinucleotide and NADP+ pyrophosphate binding sites (characteristic of mammalian FMOs) starting at positions 9 and 191, respectively. The mouse FMO3 protein sequence was 79 and 82% identical to the human and rabbit FMO3 sequences, respectively. Mouse FMO3 was expressed in Escherichia coli and compared to E. coli expressed human FMO3. The FMO3 proteins migrated with the same mobility ( approximately 58 kDa) as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. The expressed FMO3 enzymes (mouse and human forms) were sensitive to heat and reacted in a similar manner toward metal ions and detergent. Catalytic activities of mouse and human FMO3 were high toward the substrate methimazole; however, in the presence of trimethylamine and thioacetamide, FMO-dependent methimazole oxidation by both enzymes was reduced by greater than 85%. Other substrates which inhibited methimazole oxidation were thiourea and thiobenzamide and to a lesser degree N,N-dimethylaniline. When probed with mouse FMO3 cDNA, FMO3 transcripts were detected in hepatic mRNA samples from female mice, but not in samples from males. FMO3 was detected in mRNA samples from male and female mouse lung, but FMO3 message was not detected in mouse kidney sample from either gender. Results of immunoblotting confirmed the tissue- and gender-dependent expression of mouse FMO3.

Amino Acid Sequence↗
PubMed1997

Regulation of mouse liver flavin-containing monooxygenases 1 and 3 by sex steroids.

Based on enzyme activity, protein levels, and mRNA levels, we have previously demonstrated the female-predominant, female-specific, and gender-independent expression in mouse liver of FMO forms 1, 3, and 5, respectively. This study investigated the roles of testosterone, 17 beta-estradiol, and progesterone in the regulation of hepatic FMOs. FMO expression was examined in gonadectomized CD-1 mice, normal CD-1 mice receiving hormonal implants, and gonadectomized mice receiving various hormonal treatments. Following castration of males, hepatic FMO activity levels were significantly increased and serum testosterone levels significantly decreased; however, administration of physiological levels of testosterone to castrated animals returned FMO activity and testosterone concentrations to control levels. When sexually intact and ovariectomized female mice were treated with testosterone, their hepatic FMO activity levels were reduced to those of their male counterparts, concomitant with high serum testosterone levels. In males, castration dramatically increased FMO3 and FMO1 expression, and testosterone replacement to castrated males resulted in ablation of FMO3 expression. In addition, testosterone administration to females (sexually intact and gonadectomized animals) reduced FMO1 expression and obviated FMO3 expression. In females, ovariectomy alone slightly reduced FMO activity, indicative of a possible stimulatory role of female sex steroids; however, female FMO isozyme expression was relatively unchanged, and hormone replacement therapy to ovariectomized females had no discernible effect. In males and females, FMO5 levels were unaffected by gonadectomy or hormone administration, thus indicating a sex hormone-independent mechanism of regulation for this isoform. Interestingly, FMO1 protein levels were increased in sexually intact males following treatment with 17 beta-estradiol; however, only a slight increase in FMO3 protein level was observed. No positive hormone effectors of female FMO expression were identified.

Animals↗
PubMed1997

Regulation of hepatic CYP1A isozymes by piperonyl butoxide and acenaphthylene in the mouse.

The regulation of CYP1A1 and CYP1A2 isozymes by piperonyl butoxide (PBO) and acenaphthylene (ACN) was studied in the liver of male C57BL/6 and DBA/2 mice. These two cytochrome P450 genes are known to be regulated by the aromatic hydrocarbon-responsive receptor (AHR); however, it has been suggested that CYP1A2 is also induced by an AHR-independent mechanism. In this study, PBO induced hepatic CYP1A1 considerably more in C57BL/6 (Ahrb-I) than in DBA/2 (Ahrd) mice. In addition, the superinduction of CYP1A1 in wildtype hepa1c1c7 cells, which is AHR-dependent, resulted from PBO and cycloheximide treatment of the cells. In other studies in this laboratory using AHR knock-out (AHR-/-) mice, a hybrid of 129/SV and C57BL/6 strains, no induction of CYP1A1 occurred with PBO or ACN. [D.-Y. Ryu, P.E. Levi, P. Fernandez-Salguero, F.J. Gonzalez, E. Hodgson, Mol. Pharmacol., 50 (1996) 443-446.] ACN, however, did not induce CYP1A1 under the experimental conditions used. These results suggest that PBO, but not ACN, induces CYP1A1 through a weak activation of AHR. On the other hand, hepatic CYP1A2 mRNA and hnRNA were induced by PBO in both C57BL/6 and DBA/2 strains, but were not induced by ACN, a strong inducer of CYP1A2 in the B6C3F1 strain. However, both PBO and ACN induced CYP1A2 in AHR-/- mice. It is assumed, therefore, that the transcriptional induction of CYP1A2 by PBO and ACN is AHR-independent. In addition, the induction of CYP1A2 by ACN depends upon the strain of mice. Immunohistochemical studies for CYP1A1/CYP1A2 apoproteins showed that PBO induced CYP1A1/CYP1A2 around the central veins as did 3-methylcholanthrene (3-MC). The induction of CYP1A1/CYP1A2 by ACN, however, was not observed, consistent with the northern blot results.

Acenaphthenes↗
PubMed1997

Cytochrome P450 (CYP)9A1 in Heliothis virescens: the first member of a new CYP family.

A novel cytochrome P450 cDNA with its complete coding sequence and part or all of the 3' (77 nucleotides) and 5' (87 nucleotides) non-coding sequence was isolated from the tobacco budworm, Heliothis virescens (F). The 1763 nucleotide sequence encodes a protein of 532 amino acids which includes a hydrophobic N-terminal region and the highly conserved heme binding regions typical of P450s. Low sequence similarity to other P450 sequences and the presence of a thromboxane synthase-like insertion upstream from the I helix resulted in its assignment as the first member of family 9, i.e. CYP9A1. CYP9A1 is most similar to CYP3A1 from the rat (34.7% identity), but is also similar to the insect P450s from family 6, including CYP6B1v1 from Papilio polyxenes (33.3%), CYP6A2A from Drosophila melanogaster (32.4%), CYP6A3 from Musca domestica (31.7%) and CYP6B2 from Helicoverpa armigera (30.1%). Comparative Western and Northern blot studies indicate that expression of CYP9A1 in thiodicarb selected populations of tobacco budworm is associated with insecticide resistance. The pattern of restriction fragment length polymorphism (RELP) variation in offspring of single-pair matings demonstrated autosomal inheritance of CYP9A1 and enabled its assignment to linkage group 7. The coding region of CYP9A1 occupies no more than 10 kb in the tobacco budworm genome.

Amino Acid Sequence↗
PubMed1996

Xenobiotic biotransforming enzymes in the central nervous system: an isoform of flavin-containing monooxygenase (FMO4) is expressed in rabbit brain.

The flavin-containing monooxygenase (FMO, EC 1.14.13.8) is involved in the metabolism of a number of important xenobiotics including many which affect the central nervous system (CNS). Recently, reports in the literature concerning the amount, activity, location, and isozyme characteristics of this enzyme in the brain have presented conflicting evidence. In order to resolve some of the controversy surrounding FMO in the brain, a highly sensitive method for the detection of flavin-containing monooxygenase (FMO) mRNA in whole brain was employed. A poorly conserved region of FMO transcripts was used to design five sets of oligonucleotide primers. Each primer set was specific for one of the five currently known isoforms of FMO. Four and five isoforms, respectively, are expressed in rabbit liver and kidney, as determined by reverse transcription-polymerase chain reaction. However, only one set of primers amplified a specific rabbit brain cDNA fragment. The sequence of the amplification produced affirmed its identity as a segment of FMO4 cDNA. Thus, the FMO of rabbit brain may consist of a single, as yet uncharacterized isozyme and, contrary to several recent reports, is likely to be expressed at low levels.

Animals↗
PubMed1996

Monooxygenase, Esterase, and Glutathione Transferase Activity Associated with Azinphosmethyl Resistance in the Tufted Apple Bud Moth, Platynota idaeusalis

Azinphosmethyl-selected tufted apple bud moths were compared to susceptible and reverted strains with respect to possible metabolic mechanisms of resistance within the third instar, fifth instar, and adults. Based upon bioassays conducted by topical application with azinphosmethyl, LD50s were as high as 867-fold in the selected strain as compared to that seen in susceptible bud moths. The LD50 of the reverted strain was intermediate to that of the susceptible and selected insects at all stages studied. Glutathione transferase activity measured with 1-chloro-2,4-dinitrobenzene was elevated in the selected strain 1.6- and 2.2-fold as compared to third and fifth stadium susceptible bud moths, respectively. No consistent strain differences were noted for 1,2-dichloro-4-nitrobenzene. Cytochrome P450 content and P450 mRNA was not significantly different in fifth instars of the susceptible and selected strain. However, there was a 2.7- and 1.9-fold increase in benzphetamine and p-nitroanisole metabolism, respectively, in the guts of azinphosmethyl-selected fifth instars. Benzo[a]pyrene metabolism was elevated 2.4-fold in the carcass of selected bud moths and no differences were noted for methoxyresorufrin in either gut or carcass. Susceptible fifth instars demonstrated a reduced rate of metabolism of azinphosmethyl to the oxon and methyl benzazamide. Piperonyl butoxide failed to synergize azinphosmethyl toxicity. Esterase activity measured with 1-naphthyl acetate and p-nitrophenyl acetate was elevated in selected larvae compared to that seen in susceptible tufted apple bud moths in both larvae and adults. This increased esterase activity was attributed to several isoforms as resolved by analytical isoelectric focusing. One of these forms was consistently overexpressed in all of the life stages examined. Pretreatment of selected fifth instars with S,S,S-tributylphosphorotrithioate increased the toxicity of azinphosmethyl 400-fold and had minimal effect on toxicity in susceptible insects. It appears that multiple hydrolases are the primary metabolic factor in azinphosmethyl resistance in the tufted apple bud moth.

Journal Article↗
PubMed1996

Pesticides: an important but underused model for the environmental health sciences.

Pesticides are high-volume, widely used, environmental chemicals and there is continuous debate concerning their possible role in many chronic human health effects. Because of their known structures, known rates of application, and the presence of a large occupationally exposed population, they are not only important in their own right but are ideal models for the effects of environmental chemicals on the population in general. For reasons that are not always clear, this potential has not been realized. These exposed populations represent an underused asset in the study of the human health effects of environmental contaminants. Chronic effects thought to involve pesticides include carcinogenesis, neurotoxicity, and reproductive and development effects. In this paper we attempt to summarize this concern and, relying to a large extent on studies in our own laboratory, to indicate the importance and present status of studies of the mammalian metabolism of pesticides and indicate the need for further use of this model. Aspects considered include the role of pesticides as substrates for xenobiotic-metabolizing enzymes such as cytochrome P450 and the flavin-containing monooxygenase and their role as inducers or inhibitors of metabolic enzymes. The interaction of pesticides with complex multienzyme pathways, the role of biological characteristics, particularly gender, in pesticide metabolism, and the special role of pesticides at portals of entry and in target tissues are also considered.

Abnormalities, Drug-Induced↗
PubMed1996

Piperonyl butoxide and acenaphthylene induce cytochrome P450 1A2 and 1B1 mRNA in aromatic hydrocarbon-responsive receptor knock-out mouse liver.

It has been suggested that acenaphthylene (ACN), piperonyl butoxide (PBO) and other methylenedioxyphenyl (benzodioxole) compounds can function as aromatic hydrocarbon-responsive receptor (AHR)-independent inducers of the cytochrome P450 (CYP) 1A2 in mouse liver. Although much indirect evidence has supported this hypothesis, direct proof was lacking until the present study. PBO and ACN were used to examine the expression of CYP1A1, CYP1A2 and CYP1B1 in mouse liver. These three CYP isozymes are included in the AHR battery of proteins. In this study, AHR knock-out mice were dosed intraperitoneally with PBO (200 mg/kg) or ACN (100 mg/kg). Induction of hepatic CYP1A1 by PBO or ACN was not detected by northern blots. In contrast, both CYP1A2 and CYP1B1 mRNA, constitutively expressed at low levels in this tissue, were induced by each compound in the livers of AHR knock-out mice. In addition, the use of heterogenous nuclear RNA reverse transcription-polymerase chain reaction procedures revealed that the transcriptional activities of CYP1A2 were increased by PBO and ACN treatments. These results show that AHR-independent pathway(s) can be involved in induction of CYP1A2 and CYP1B1.

Acenaphthenes↗
PubMed1995

Biphasic responses in synergistic interactions.

Synergistic reactions, as exemplified by the methylenedioxyphenyl (benzodioxole) insecticide synergists, are one of the more studied interactions between toxicants. This group of chemicals includes, in addition to synergists such as piperonyl butoxide, carcinogens such as safrole and isosafrole and many compounds occurring naturally in foods, such as myristicin and piperine. These compounds may function as cytochrome P450 substrates, inhibitors and/or inducers. The biphasic curve in cytochrome P450 activities following a single dose is the result of an initial inhibitory phase followed by a phase of induction, with an eventual return to baseline levels. Both inhibition and induction may be isozyme-specific and different isozymes may be involved in the two activities of the same chemical. Details of these activities are presented and their significance is discussed.

Animals↗
PubMed1995

Regulation of cytochrome P-450 isozymes CYP1A1, CYP1A2 and CYP2B10 by three benzodioxole compounds.

Three benzodioxole (BD) compounds were used to investigate the structural requirement for regulation of the cytochrome P450 isozymes, CYP1A1, CYP1A2 and CYP2B10, in mouse liver. Male mice (C57BL/6) were treated intraperitoneally for 3 days with 5-t-butyl-1,3-benzodioxole (t-BBD), 5-n-butyl-1,3-benzodioxole (n-BBD) and 5-(3-oxobutyl)-1,3-benzodioxole (o-BBD). t-BBD-induced liver microsomes showed the highest pentoxyresorufin O-dealkylation (PROD) activity, while o-BBD induced microsomes showed slightly higher activity in ethoxyresorufin O-deethylation (EROD), benzo[a]pyrene hydroxylation (BaP-OH) and acetanilide hydroxylation (Acet-OH) assays. In vitro enzyme inhibition assays showed that n-BBD inhibited EROD and Acet-OH activities more than either o-BBD or t-BBD, while PROD activity was evenly inhibited by all three compounds. Western and northern blots showed that CYP1A1 was not detectably induced by any of the three BD compounds. The levels of CYP1A2 protein and mRNA were increased in all three treated livers. In addition to CYP1A2 induction, t-BBD also induced the protein and mRNA for CYP2B10.

Animals↗
PubMed1995

Gender differences in hepatic expression of flavin-containing monooxygenase isoforms (FMO1, FMO3, and FMO5) in mice.

Hepatic flavin-containing monooxygenase (FMO) activity of microsomes from adult CD-1, Swiss-Webster, C57BL/6, and DBA/2 mice was found to be significantly higher in females than in males. Based on protein and mRNA levels in CD-1 mice, FMO forms responsible for the gender difference in FMO activity were FMO1 and FMO3. FMO1 expression was two to three times higher in female mice compared with males; FMO3, however, which was expressed at levels equivalent to FMO1 in female mice, was not detected in males. The expression of FMO5 was approximately equal in both sexes. FMO2 and FMO4 transcripts were not evident in hepatic mRNA from mice. Protein and mRNA levels appear to be coregulated with regard to gender-selective or gender-specific expression of FMO1 or FMO3, respectively. FMO5, which demonstrates no gender-selective expression in mice, may be regulated by different mechanisms. Examination of protein levels among Swiss-Webster, C57BL/6, and DBA/2 strains revealed a gender-dependent expression of FMO isozymes identical to the CD-1 strain.

Animals↗
PubMed1995

Pesticide-metabolizing enzymes.

Pesticides are known to function as substrates, inhibitors and inducers of drug-metabolizing enzymes, with the same compound frequently acting in more than one of these roles. Current studies of phase I metabolism of pesticides include cytochrome P450 (P450) and the flavin-containing monooxygenase (FMO), with particular reference to individual isozymes. In mouse liver, the level of FMO1 is gender dependent, FMO3 is gender specific, while FMO5 appears to be gender independent. The isozyme specificity of methylenedioxyphenyl synergists for induction of P450 in mouse liver involves P450s 1A1, 1A2 and 2B10, including a non-Ah receptor-dependent mechanism for 1A2 induction. The substrate specificity of mouse and human P450 and FMO isozymes is discussed.

Animals↗
PubMed1995

Metabolism of thioridazine by microsomal monooxygenases: relative roles of P450 and flavin-containing monooxygenase.

1. The metabolism of thioridazine by the flavin-containing monooxygenase (FMO) of mouse liver and several P450 isozymes was examined using microsomes, purified FMO, and expressed P450 isozymes. Metabolites were identified by hplc. 2. Thermal inactivation and antibodies to NADPH P450 reductase were used to selectively inactivate FMO and P450 respectively. Inactivation of FMO by heat-treatment reduced the formation of thioridazine-N-oxide and northioridazine, whereas inactivation of P450 resulted in decreased amounts of thioridazine-2-sulphoxide, northioridazine, and thioridazine-5-sulphoxide. 3. Liver microsomes from mouse induced with phenobarbital, 3-methylcholanthrene, or acetone were compared with control microsomes. Phenobarbital induction resulted in increased formation of all metabolites except thioridazine-N-oxide, while retaining a general metabolic profile similar to that achieved with control microsomes. Neither 3-methylcholanthrene nor acetone induction had any effect on the in vitro metabolism of thioridazine. 4. FMO purified from mouse liver produced thioridazine-N-oxide as the major metabolite. 5. Preliminary experiments with commercially prepared microsomes made from cells expressing recombinant human liver P450 2D6 and 3A4 suggested that thioridazine is metabolized by 2D6 but not 3A4.

Animals↗
PubMed1994

A nomenclature for the mammalian flavin-containing monooxygenase gene family based on amino acid sequence identities.

A nomenclature based on comparisons of amino acid sequences is proposed for the members of the mammalian flavin-containing monooxygenase (FMO) gene family. This nomenclature is based on evidence of a single gene family composed of five genes. The percentage identities of the amino acid sequences of the five known forms of mammalian FMO are between 52 and 57% in rabbit and between 50 and 58% across species lines. The identities of all orthologs are greater than 82%. There is no evidence for multiple, highly related forms of the enzyme or for more than one mammalian FMO gene family. In the proposed system, the mammalian flavin-containing monooxygenase gene family is designated as "FMO" and the individual genes are distinguished by an Arabic numeral. The FMOs known as the "liver" and "lung" enzymes become FMO1 and FMO2, and the more recently described forms of the enzymes become FMO3, FMO4, and FMO5. Human FMO gene designations, FMO1 and FMO3, remain unchanged, but the gene designated FMO2 becomes FMO4. Following convention, the genes and cDNA designations will be italicized and the mRNA and protein designations will be nonitalicized. The purpose of the proposed nomenclature is to provide for the unambiguous identification of orthologous forms of mammalian FMOs, regardless of the species or tissue in question. The proposed classification considers only members of the mammalian flavin-containing monooxygenase gene family and has no bearing on the generally accepted definition of a multisubstrate flavin-containing monooxygenase.

Amino Acid Sequence↗