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Biomedical subjects

J R Gillette

Publications and source records attributed to J R Gillette.

At least 19 recordsLinked to original sources
PubMed2000

Laboratory of Chemical Pharmacology, National Heart, Lung, and Blood Institute, NIH: a short history.

The Laboratory of Chemical Pharmacology (LCP) began in 1950 as the Section of Pharmacology within the National Heart Institute, the National Institutes of Health. Its first chief was Bernard B. Brodie, considered by many to be one of the fathers of modern pharmacology. Since its inception, LCP has made many significant contributions to the fields of pharmacology and toxicology. LCP was among the first to study (a) the effects of drugs on the turnover of serotonin and norepinephrine in brain and other tissues, (b) the absorption of drugs from the gastrointestinal tract and their passage across the blood-brain barrier, (c) the oxidation and reduction of drugs and other foreign compounds by liver microsomal enzymes (later known as the cytochrome P450 enzymes) and inhibitors and inducers of these enzymes, (d) the formation of toxic chemically reactive metabolites of drugs and other foreign compounds, and (e) mechanisms of immunological responses. Approximately 300 scientists worked in LCP during its existence, and they and their collaborators published more than 1,300 papers. This is a short history of the people who worked in it and of their contributions to biomedical sciences.

Animals↗
PubMed1995

Isotope effect studies on the cytochrome P450 enzymes.

Isotope effect experiments provide a powerful tool for study of the fundamental aspects of the enzymology of the cytochrome P450 enzymes. Competition between alternate pathways not only allows P450 isotope effects to be observed, but also provides mechanistic information on both oxygen activation and substrate oxidation. Indeed, the kind of knowledge that isotope effect studies can provide is not readily obtainable by other methodologies.

Animals↗
PubMed1994

Theory for the observed isotope effects on the formation of multiple products by different kinetic mechanisms of cytochrome P450 enzymes.

Cytochrome P450 systems are unusual in that many of them can convert a substrate to a number of different metabolites. Several kinetic mechanisms may be envisioned by which the metabolites may be formed. In each of the mechanisms, the substrate combines with the enzyme in different orientations to form a set of (ES) complexes that then are activated to a set of (EOS) complexes. The fate of these (EOS) complexes determines the kinetic mechanism. In the "parallel pathway" mechanism, the (EOS) complexes are so stable and rigid they cannot be converted either directly or indirectly to complexes with different orientations; the orientation of the (ES) complexes thus determines which metabolite will be formed. In the "nondissociative" mechanisms, the complexes are not rigid; instead they undergo interconversion while the substrate remains in the active site of the enzyme. In the "dissociative" mechanisms, the (EOS) complexes dissociate to (EO) and (S), but recombine to form (EOS) complexes with either the same or different orientations. Steady-state equations describing the deuterium isotope effects for these kinetics mechanisms have been derived and solved for competitive experiments, in which equal concentrations of both deuterated and nondeuterated substrates are present in incubation mixtures, and for noncompetitive experiments, in which only one of the substrates is present. The equations reveal that comparisons of the isotope effects on the formation of a metabolite by a pathway that does not involve the abstraction of a deuterium from a deuterated substrate (the non-deuterium abstraction pathway) in both experiments can differentiate between the kinetic mechanisms. A value of 1.0 for (v)H/(v)D in the competitive experiment, but < 1.0 to > 1.0 for the value of (Vmax/Km)H/(Vmax/Km)D in the noncompetitive experiment, is diagnostic for the "dissociative" mechanisms. Values of 1.0 in both kinds of experiments are diagnostic for the "parallel pathway" mechanism. Values of < 1.0 in both types of experiments are diagnostic for the "nondissociative" mechanisms. The equations also predict possible unusual substrate-inhibitor interactions when the "dissociative" mechanism is operative.

Binding, Competitive↗
PubMed1994

Deuterium isotope effects on A-ring and D-ring metabolism of testosterone by CYP2C11: evidence for dissociation of activated enzyme-substrate complexes.

Cytochrome P450 systems are unusual in that many of them can convert a substrate to a number of different metabolites by several possible kinetic mechanisms. Steady-state equations describing the deuterium isotope effects for mechanisms in which different orientations of the substrate relative to the perferryl oxygen in the active site of the enzyme are achieved before a hydrogen (or possibly an electron) is abstracted have been derived and solved (Gillette et al., 1994). These equations have been used to elucidate the kinetic mechanisms by which CYP2C11 converts testosterone to 2 alpha-hydroxytestosterone on the one hand and 16 alpha-hydroxytestosterone and androstenedione on the other. We have synthesized testosterone-2,2,4,6,6-2H5 and compared its metabolism by CYP2C11 with that of nondeuterated testosterone. In this system, deuterated 2 alpha-hydroxytestosterone would be formed by a deuterium abstraction pathway via the active oxygen intermediate (EOSw) and the D-ring metabolites would be formed by non-deuterium abstraction pathways from active oxygen intermediates represented by (EOSx). The results revealed that testosterone in the activated enzyme-substrate complexes, (EOSw) and (EOSx), does not change orientations while it is in the active site of CYP2C11. Instead, two of the noncompetitive experiments indicated that testosterone is able to dissociate from the (EOS) complexes and reassociate in either the same or different orientations. A third noncompetitive experiment suggested that testosterone in the (EOS) complexes does not change orientations while it is in the active site of CYP2C11, nor does it dissociate from the (EOS) complexes; instead, the pattern of metabolite formation is governed almost solely by the orientation of testosterone in the (ESw) and ESx) complexes.

Aryl Hydrocarbon Hydroxylases↗
PubMed1991

Mouse pulmonary cytochrome P-450 naphthalene hydroxylase: cDNA cloning, sequence, and expression in Saccharomyces cerevisiae.

We have isolated a cDNA clone, Nah-2, encoding the cytochrome P-450Nah (naphthalene hydroxylase) from a mouse lung lambda ZAP cDNA library using anti-cytochrome P-450Nah IgG as a probe. This same antibody selectively blocked [Nagata, K., Martin, B.M., Gillette, J.R., & Sasame, H.A. (1990) Drug Metab. Dispos. 18, 557-564] the cytochrome P-450 in mouse lung microsomes that catalyzed the conversion of naphthalene to (1R,2S)-naphthalene 1,2-oxide, which has been postulated as a causative agent in the naphthalene-induced tissue-specific necrosis of Clara cells in mouse lung. The toxic effect is seen in mouse and not in rat. The cDNA encodes a polypeptide of 491 amino acids with a molecular mass of 50 kDa. Northern blot analysis with an Nah-2-specific probe revealed that the mRNA is expressed in a species- and tissue-specific manner, present only in mouse lung and liver and not in that of rat. The mRNA encoding Nah-2 is constitutively expressed and is not induced by either phenobarbital, pyrazole, pregnenolone 16 alpha-carbonitrile, or 3-methylcholanthrene. Comparative amino acid sequence analyses with other documented members of the P-450 gene superfamily revealed that this encoded protein is in the IIF subfamily. To analyze its substrate specificity, the cDNA was inserted into the vector, pAAH5, and expressed in the Saccharomyces cerevisiae strain, AH22. The presence of cytochrome P-450Nah in the microsomes isolated from transformed cells and analyzed by Western blot was confirmed by immunocomplexing product with anti-cytochrome P450Nah IgG. Furthermore, activity toward naphthalene in the microsomes from the transformed cells established that this clone encodes a naphthalene hydroxylase.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

Theoretical studies on the mechanism of conversion of androgens to estrogens by aromatase.

Semiempirical molecular orbital calculations (AM1) were used to model several possible reaction mechanisms for the third oxidation of the aromatase-catalyzed conversion of androgens to estrogens. The reaction mechanisms considered are based on the assumption that the third oxidation is initiated by 1 beta-hydrogen atom abstraction. Homolytic cleavage of the C10-C19 bond was modeled for both the 3-keto and 2-en-3-ol forms of the androgen 1-radicals. The addition of a protein nucleophile to the 19-oxo intermediate was also considered, and -OCH3, -SCH3, and -NHCH3 were used to represent the Ser, Cys, and Lys adducts. The transition states were estimated and optimized from the reaction coordinates obtained by constraining and increasing the C10-C19 bond lengths. The enthalpies of activation range from 14 to 21 kcal and are approximately 2 kcal lower for cleavage of the enol form. Given the tendency for AM1 to overestimate activation energies, all reactions may be energetically accessible. Other reactions modeled include a homolytic cleavage reaction from a thioether radical cation and the direct additions of oxygen radical compounds to the carbonyl of the 1-radical-2-en-3-ol-19-oxo androgen. A mechanism is proposed in which the 19-oxo intermediate is subject to initial nucleophilic attack by the protein. Since rotation of the 19-carbonyl can bring the oxygen within 2.1 A of the 2 beta-hydrogen, the formation of a tetrahedral intermediate can occur with concomitant removal of the 2 beta-proton. Enolization activates the C1-position for hydrogen atom abstraction, since the resulting radical is resonance stabilized.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgens↗
PubMed1989

Theory for the observed isotope effects from enzymatic systems that form multiple products via branched reaction pathways: cytochrome P-450.

By use of cytochrome P-450 as the prototype, kinetic descriptions are derived for the observed isotope effects for several models of enzymatic systems which are capable of generating multiple products from single substrates. The models include rapid and slow equilibria between enzyme-substrate orientations as well as multiple simultaneous and multiple sequential isotope effects. When an equilibrium is established between enzyme-substrate complexes that are responsible for the oxidation of different positions of the substrate, the kinetics can be represented by competing pathways from the same intermediate. When direct interchange between the complexes does not occur, the alternate pathway mimics the presence of a competitive inhibitor in the substrate solution. In general, the presence of alternate pathways in competition with the isotopically sensitive step will tend to unmask the intrinsic isotope effect.

Binding, Competitive↗
PubMed1986

Final report of the Color Additive Scientific Review Panel.

The Color Additives Scientific Review Panel considered whether there was information sufficient to perform a carcinogenic risk assessment on the colors D&C Red No. 19 (R-19), D&C Red No. 37 (R-37), D&C Orange No. 17 (O-17), D&C Red No. 9 (R-9), D&C Red No. 8 (R-8) and FD&C Red No. 3 (R-3) and to evaluate the assessments sent to FDA as part of the petitions for use of the colors for drug and external uses by the Cosmetic, Toiletry and Fragrance Association (CTFA). There is a lack of human data concerning the colors for making a human health assessment, so the assessments are based upon the extrapolation of animal data. The risk assessments are determined for exposure to single chemicals. Excluded from consideration are possible effects from exposure to multiple chemicals, such as co-carcinogenesis, promotion, synergism, antagonism, etc. In the light of recent efforts in establishing a consensus in risk assessment, the Panel has determined that the CTFA assessments for R-10, O-17, and R-9 are consistent with present acceptable usages, although it questions some of the assumptions used in the assessments. The Panel identified a number of general assumptions made, and discusses their validity, their impact on total uncertainty, and the potential options to address the gaps in understanding that necessitate the assumption. The Panel also derived revised risk estimates using more "reasonable" assumptions than "worst-case" situations, for 90th percentile and average exposure. For those assumptions that are easily quantifiable, the Panel's estimates are less than an order of magnitude lower than the CTFA risk estimates, indicating that the underestimates and overestimates of the CTFA risk estimates tend to balance each other. The impact of most of the assumptions is not quantifiable. The assessment for R-3 is complicated by the fact that there is no good skin penetrance study for this color. It was assumed that the penetrance is similar to that of another water-soluble xanthene color, R-19. It is expected that the absorption of the color is not likely to exceed that of the smaller molecule, R-19. Therefore, the risk estimates are similar to the CTFA estimates, but with different reasoning. The estimates for R-8 and R-37 are different from the others in that there is a lack of any exposure or toxicological information on these colors.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Immunological studies on the mechanism of halothane-induced hepatotoxicity: immunohistochemical evidence of trifluoroacetylated hepatocytes.

The fulminant hepatotoxicity caused by halothane has been thought to have an immunological basis because this toxicity occurs most often after repeated administration of halothane and because sera from patients recovering from severe halothane hepatotoxicity contain antibodies that bind to the surface membranes of hepatocytes of rabbits treated with halothane. In order to determine whether the major reactive metabolite of halothane, trifluoroacetyl halide, covalently binds to hepatocytes, we have developed specific and sensitive peroxidase enzyme-linked immunosorbent assays and an indirect immunofluorescence staining method for identifying trifluoroacetylated (TFA)-hepatocytes. Liver sections prepared from rats at 4 hr after halothane administration were stained preferentially in the centrilobular region with anti-TFA serum whereas livers of control rats showed no staining. The specificity of the assay for the TFA group was confirmed by the complete inhibition of the staining with 200 microM N-epsilon-TFA-L-lysine in the diluted antiserum. On the other hand, 2 mM halothane or L-lysine did not inhibit this staining. Moreover, treatment of rats with deuterated halothane resulted in significantly less staining than did halothane. At 24 hr after halothane administration, hepatocytes isolated and stained by indirect immunofluorescence showed a linear and granular pattern on their surface membranes. These results indicate that trifluoroacetyl halide either reacts directly with constituents of the plasma membranes or with other cellular components which become incorporated into the plasma membranes.

Animals↗
PubMed1985

Immunochemical evidence of trifluoroacetylated cytochrome P-450 in the liver of halothane-treated rats.

Four hours after the administration of halothane to phenobarbital-pretreated rats, subcellular fractions of liver were isolated and the proteins in the fractions were separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis, transferred to nitrocellulose sheets, and immunochemically stained with anti-trifluoroacetylated antibodies. The microsomal fraction contained the highest level of trifluoroacetylated adducts. Its major trifluoroacetylated component was immunochemically identified as a phenobarbital-inducible form of cytochrome P-450 (54 kDa), whereas the other observed trifluoroacetylated protein fraction (59 kDa) was not identified. The plasma membrane fraction also contained a 54-kDa trifluoroacetylated adduct, which was immunochemically related to the 54-kDa cytochrome P-450. Microsomes from untreated rats that were administered halothane contained only the 59-kDa trifluoroacetylated protein fraction. The specificity of the immunochemical staining for the bound oxidative metabolite of halothane was confirmed by the finding that rats treated with deuterated halothane had considerably less stained liver proteins than did those treated with halothane. These results suggest that the CF3COX oxidative metabolite of halothane is so reactive that it binds predominantly to the cytochrome P-450 that produced it.

Acetylation↗
PubMed1984

The role of ortho-bromophenol in the nephrotoxicity of bromobenzene in rats.

ortho-Bromophenol (1.92 mmol/kg, ip) caused a 50% decrease in renal glutathione levels within 90 min. In contrast, hepatic glutathione levels remained 80% of control values 5 hr after ortho-bromophenol administration. Renal glutathione was far more susceptible to the initial rapid depleting effects of ortho-bromophenol than was hepatic glutathione, the dose-response curve for hepatic glutathione depletion being shifted to the right. ortho-Bromophenol at doses greater than 1.6 mmol/kg caused severe renal necrosis in noninduced rats, with consequent elevations in BUN levels. This dose was one-fifth as large as that required by bromobenzene to produce a similar necrosis in phenobarbital-treated rats (W. D. Reid, Exp. Mol. Pathol., 19, 197-214, 1973). Phenobarbital pretreatment and depletion of tissue glutathione with diethyl maleate caused significant increases in BUN levels over controls. Pretreatment with piperonyl butoxide decreased the incidence of elevated BUN levels following ortho-bromophenol administration. While liver microsomes converted ortho-bromophenol to covalently bound material, kidney microsomes did not. However, in vivo, ortho-bromophenol covalently bound to kidney protein of control rats four times greater than to liver protein. Phenobarbital pretreatment increased the in vivo covalent binding to kidney protein but not to liver protein. The degree of covalent binding to kidney protein correlated with BUN levels (r = 0.91, p less than 0.001). The nature of the nephrotoxic metabolite of ortho-bromophenol is not known, but an intermediate may be generated in the liver and transported to the kidney. These findings suggest that ortho-bromophenol may play a role in the nephrotoxicity observed following bromobenzene administration.

Animals↗