Search PubMed⌕ Search

Biomedical subjects

J C Cook

Publications and source records attributed to J C Cook.

At least 55 records · Page 3Linked to original sources
PubMed1995

Effects of ammonium perfluorooctanoate on Leydig cell function: in vitro, in vivo, and ex vivo studies.

Ammonium perfluorooctanoate (C8) produced a dose-dependent increase in Leydig cell adenomas in Crl:CD BR (CD) rats fed 0, 30, or 300 ppm for 2 years. Administration of C8 to adult male CD rats, by gavage for 14 days, produced decreased serum and testicular interstitial fluid testosterone levels and increased serum estradiol levels. The C8-mediated decrease in the serum testosterone levels appeared to be due to a lesion at the level of the testis. These endocrine changes may play a role in the C8 induction of Leydig cell tumors. In the present work, C8 was examined for its ability to (1) directly affect Leydig cells in vitro using isolated Leydig cells from untreated rats and ex vivo using Leydig cells isolated from C8-treated rats, (2) affect testicular interstitial fluid hormone levels, and (3) induce aromatase activity. These studies were conducted to investigate the hypothesis that C8 produces an increase in estradiol by inducing cytochrome P450 XIX (aromatase), which converts testosterone to estradiol, and that the elevated estradiol levels ultimately produce Leydig cell hyperplasia and adenoma formation by acting as a mitogen or enhancing growth factor secretion. In the in vivo and ex vivo studies, adult male CD rats were gavaged with either 0 or 25 mg/kg/day C8 for 14 days. In addition to the ad libitum control, a second control group was pair-fed to the 25 mg/kg/day C8 group. In the in vitro and ex vivo studies, Leydig cells were isolated from testes of adult males by collagenase digestion followed by enrichment over Percoll gradients. A dose-dependent decrease in testosterone levels was observed in hCG-stimulated Leydig cells treated in vitro with C8 for 5 hr (IC50 approximately 200 microM). In contrast, ex vivo studies demonstrated an increase in testosterone production in hCG-stimulated Leydig cells from C8-treated rats when compared to Leydig cells isolated from either the ad libitum or pair-fed control rats. The in vitro data demonstrate that C8 directly inhibits testosterone release from Leydig cells, while the ex vivo data demonstrate that this inhibition is reversible.(ABSTRACT TRUNCATED AT 400 WORDS)

Administration, Oral↗
PubMed1995

Vaccination with yeast-expressed cottontail rabbit papillomavirus (CRPV) virus-like particles protects rabbits from CRPV-induced papilloma formation.

Papillomaviruses infect epithelia of the skin and mucous membranes and cause benign or malignant tumours in animals and in humans. The viruses are highly species-specific, and cell culture systems for propagating human papillomaviruses (HPVs) do not exist. However, there are several animal papillomavirus models. In the cottontail rabbit papillomavirus (CRPV) system, we demonstrated that recombinant CRPV virus-like particles (VLPs) consisting of the capsid proteins L1 or L1+L2 can be produced in the yeast Saccharomyces cerevisiae. Three immunizations with L1 VLPs formulated on aluminum adjuvant at 1-100 micrograms dose-1 efficiently protected rabbits from challenge with CRPV. Sera of immunized rabbits were shown to contain high-titered serum antibodies to CRPV L1 VLPs and to neutralize CRPV in vitro. Our results suggest that recombinant yeast-derived VLPs could be the basis for a candidate HPV vaccine.

Animals↗
PubMed1995

Effects of superoxide on nitric oxide-dependent N-nitrosation reactions.

Recent studies have demonstrated that nitric oxide (NO) in the presence of superoxide (O2-) may mediate mutagenesis via the N-nitrosation of DNA bases followed by nitrosative deamination to yield their hydroxylated derivatives. We have found that phorbol myristate acetate (PMA)-activated extravasated rat neutrophils (PMNs) will N-nitrosate 2,3-diaminonaphthalene (DAN) to yield its highly fluorescent nitrosation product 2,3-naphthotriazole (triazole) via the L-arginine dependent formation of NO. Addition of SOD enhanced triazole formation suggesting that O2- production may inhibit the N-nitrosating activity and thus the mutagenic activity of inflammatory PMNs. The objective of this study was to assess the role of superoxide as a modulator of NO-dependent N-nitrosation reactions using PMA-activated PMNs as well as a chemically defined-system that generates both NO and superoxide. We found that PMA-activation of PMNs reduced found that PMA-activation of PMNs reduced the amount of N-nitrosation of DAN by approximately 64% when compared to non-stimulated cells (450 vs. 1250 nM). Addition of SOD but not inactivated SOD or catalase to PMA-activated PMNs enhanced the formation of triazole by approximately 4-fold (1950 nM). In addition, we found that the NO-releasing spermine/NO adduct (Sp/NO; 50 microM) which produces approximately 1.0 nmol NO/min generated approximately 8000 nM of triazole whereas the combination of Sp/NO and a superoxide generator (hypoxanthine/xanthine oxidase) that produces approximately 1.0 nmol O2-/min reduced triazole formation by 90% (790 nM). Addition of SOD but not catalase restored the N-nitrosating activity. We conclude that equimolar fluxes of superoxide react rapidly with NO to generate products that have only limited ability to N-nitrosate aromatic amino compounds and thus may have limited ability to promote mutagenesis via the nitrosative deamination of DNA bases.

2-Naphthylamine↗
PubMed1994

Chromatographic separation of low-molecular-mass recombinant proteins and peptides on Superdex 30 prep grade.

The chromatographic properties of Superdex 30 prep grade medium have been investigated in non-denaturing and denaturing mobile phases using commercially available proteins and peptides as well as low-molecular-mass (M(r)) recombinant polypeptides. The medium is a macroreticular gel composed of crosslinked agarose beads to which dextran has been covalently bound. The mean particle size is approximately 34 microns. Experimental results show a linear relation between the distribution coefficient (KD) and the log10 M(r) in the fractionation range 24,000-3000. The relationships between resolution and flow-rate or load volume were investigated and shown to be comparable with those of Superdex 75 and 200 prep grade media. Minimal loss of resolution occurred in the flow-range from 30-60 cm/h. Load volumes of up to 5% total column volume could be applied while maintaining baseline resolution of polypeptide mixtures. Non-specific interactions between the matrix and certain samples were characterized. The predominant interactions with the resin appear to be hydrophobic in nature rather than ionic. Hydrogen bonding may also play a role in the retardation of certain small molecules. The applicability of the resin for separating dimeric and oligomeric forms of low-molecular-mass recombinant proteins was shown.

Amino Acid Sequence↗
PubMed1994

Mycology of nail disorders.

Cases of onychomycosis represent up to 30% of diagnosed superficial fungal infections and are caused by three groups of fungi: dermatophytes, yeasts, and nondermatophytic molds. The majority of toenail infections are caused by dermatophytes; Trichophyton rubrum is isolated with the greatest frequency. In infections of fingernails, Candida species can be isolated as frequently as the dermatophytes. Of the molds, Scytalidium species can infect both fingernails and toenails, as well as adjacent skin, and represent 3% of the nail infections in a temperate country such as the United Kingdom but a much higher proportion in tropical countries. Other molds such as Scopulariopsis, Acremonium, and Aspergillus species can infect damaged nails. The isolation of a dermatophyte is always considered indicative of infection, but the presence of other molds, which may be aerial contaminants, must be interpreted with care.

Arthrodermataceae↗
PubMed1993

Investigation of a mechanism for Leydig cell tumorigenesis by linuron in rats.

In a previously conducted 2-year study, a concentration-dependent increase in Leydig cell adenomas was observed in Crl:CD BR(CD) rats fed diets containing the herbicide linuron. Linuron has been shown to be negative in a battery of six tests for genotoxicity; therefore, a nongenotoxic mechanism of tumorgenesis was investigated. Linuron is structurally related to the nonsteroidal antiandrogen, flutamide. Flutamide has also been shown to produce Leydig cell tumors within 1 year, presumably due to sustained hypersecretion of luteinizing hormone (LH) which occurs following disruption of the hypothalamic-pituitary-testicular (HPT) axis. To investigate whether linuron possesses antiandrogenic activity, sexually immature and mature CD rats were administered either 200 mg/kg linuron or 10 mg/kg flutamide (positive control) for 2 weeks. Accessory sex organs were weighed and serum hormone levels were measured to assess androgen status and alterations in the HPT axis. Serum from a multigeneration reproduction study with linuron was also analyzed for serum hormone levels. In addition, competitive receptor binding studies were conducted to evaluate the ability of linuron to bind to the androgen receptor. Linuron decreased accessory sex organ weights in sexually immature and mature linuron-treated rats. Increased serum estradiol and LH levels were observed in sexually mature linuron-treated rats. Serum estradiol and LH levels were also elevated in P1 and F1 male rats from the multigeneration reproduction study. These accessory sex organ and hormonal changes are consistent with those seen with the antiandrogen flutamide, the only exception being serum testosterone, which was elevated following exposure to flutamide but not to linuron. The inability of linuron to increase testosterone levels may reflect the lower potency of linuron as an antiandrogen compared with that of flutamide, which is a potent antiandrogen. Additionally, linuron competed with [3H]testosterone for binding to the androgen receptor. The IC50 data for competition to the androgen receptor suggest that linuron is approximately 3.5 times less potent than flutamide. These data are consistent with the effects seen with flutamide and demonstrate that linuron is a less potent antiandrogen than flutamide. Collectively, these data support the hypothesis that linuron produces Leydig cell tumors via an antiandrogenic mechanism where sustained hypersecretion of LH appears to be responsible for the development of Leydig cell hyperplasia and adenomas.

Age Factors↗
PubMed1992

Isoforms of mammalian ubiquitin-activating enzyme.

Ubiquitin-activating enzyme, "E1," is the first enzyme in the pathway leading to formation of ubiquitin-protein conjugates and represents a potential target for regulation in the metabolic control of the conjugation reaction. Antiserum raised against human E1 recognizes two immunoreactive proteins in extracts from several human cell lines and animal tissues. We have characterized these two immunoreactive proteins in HeLa cells and present evidence that they are isoforms of E1. We have designated these isoforms as "E1(110 kDa)" and "E1(117 kDa)" to reflect their apparent molecular masses determined from SDS-polyacrylamide gel electrophoresis. These two immunoreactive proteins are immunologically similar, have nearly identical peptide maps, and comigrate with enzymatic activity characteristic of E1 in native polyacrylamide gel electrophoretic separations. Pulse-labeling experiments reveal that both isoforms are long-lived in vivo with degradation rates which are inconsistent with a proenzyme/enzyme model. Furthermore, their rates of degradation, which vary depending on the cell line studied, are kinetically distinguishable in contact-inhibited human lung fibroblasts. This work represents the first demonstration of E1 isoforms in a non-plant species and carries important implications for studies of the regulatory mechanisms controlling ubiquitin conjugation.

Animals↗
PubMed1992

Induction of Leydig cell adenomas by ammonium perfluorooctanoate: a possible endocrine-related mechanism.

Ammonium perfluorooctanoate (C8) produced an increased incidence of Leydig cell adenomas in Crl:CD BR (CD) rats fed 300 ppm for 2 years. A hormonal (nongenotoxic) mechanism was examined since C8 was negative in short-term tests for genotoxicity. Adult male CD rats were gavaged with either 0, 1, 10, 25, or 50 mg/kg C8 for 14 days. In addition, a control group was pair-fed to the 50 mg/kg C8 group. A dose-dependent decrease in body and relative accessory sex organ (ASO) weights was seen, with the relative ASO weights of the 50 mg/kg group significantly less than those of the pair-fed control. Serum estradiol levels were elevated in the 10, 25, and 50 mg/kg C8-treated animals. Estradiol levels in the 50 mg/kg C8 group were 2.7-fold greater than those in the pair-fed control. The increase in serum estradiol levels occurred at the same dose levels as the increase in hepatic beta-oxidation activity. A statistically significant downward trend with dose was seen in serum testosterone levels when compared with the ad libitum control. However, when the 50 mg/kg C8-treated rats were compared with their pair-fed control, no significant differences were seen. Challenge experiments, which can identify the presence and location of a lesion in an endocrine axis, were undertaken to clarify the significance of this downward trend in serum testosterone following C8 exposure. In the challenge experiments, adult CD rats were gavaged with either 0 or 50 mg/kg C8 for 14 days. One hour before termination, rats received either a human chorionic gonadotropin (hCG), gonadotropin-releasing hormone (GnRH), or naloxone challenge. Following hCG challenge, serum testosterone levels in the 50 mg/kg C8 were significantly decreased (50%) from those in the ad libitum controls. Similar decreases, although not significant, were seen in serum testosterone following GnRH and naloxone challenge. The challenge experiments suggest that the decrease in serum testosterone following C8 exposure is due to a lesion at the level of the testis. In addition, progesterone, 17 alpha-hydroxyprogesterone, and androstenedione were examined in the 50 mg/kg C8-treated males following hCG challenge. A 60% decrease was observed in androstenedione levels in the C8-treated animals from those in the ad libitum controls; no other differences were seen. These data suggest that the decrease in serum testosterone following hCG challenge may be due to a decrease in the conversion of 17 alpha-hydroxyprogesterone to androstenedione. The observed effects described above can be attributed to the elevated serum estradiol levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenoma↗
PubMed1992

Comparison of the effects of Wyeth-14,643 in Crl:CD BR and Fisher-344 rats.

Wyeth-14,643 (WY) belongs to a diverse class of compounds which have been shown to produce hepatic peroxisome proliferation and hepatocellular carcinoma in rodents. Based on a review of bioassay data, a relationship appears to exist between peroxisome proliferating compounds and Leydig cell adenoma formation. Most rat bioassays with peroxisome proliferators have been conducted in the Fisher-344 (F344) rat, which has a high spontaneous incidence of Leydig cell adenomas. Thus, it was necessary to use an alternative animal model to investigate this relationship further. Therefore the Crl:CD BR (CD) rat, which has a low spontaneous Leydig cell adenoma incidence, was chosen for a 2-year feeding study with WY. Before initiating this 2-year feeding study, it was necessary to investigate whether any strain differences existed between CD and F344 rats with respect to WY-induced peroxisome and cell proliferation. In this study, male CD and F344 rats were fed diets containing 0, 50, or 1000 ppm WY for 21 days. Peroxisome proliferation in the liver and testis was determined biochemically by measuring beta-oxidation activity and was confirmed ultrastructurally. Serum hormone levels and cell proliferation rates in the liver and testis were also measured. In addition, basal beta-oxidation activity and cell proliferation rates were compared between the CD and F344 rats. A significant decrease in final body weight was observed in the 1000 ppm WY groups for both CD and F344 rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Association of ubiquitin-activating enzyme with HeLa cell chromosomes during mitosis.

Ubiquitin-activating enzyme (E1) is the first enzyme in the pathway leading to formation of ubiquitin-protein conjugates. Antibodies raised against E1 were affinity purified and used for immunostaining HeLa cells. Condensed chromosomes in mitotic cells were found to be strongly immunoreactive. Chromosomes from metaphase-arrested HeLa cells were isolated and chromosome-associated proteins were analyzed by Western blotting. E1 was detected in fractions containing isolated chromosomes. These results suggest that E1 is associated with condensed chromosomes during mitosis.

Blotting, Western↗
PubMed1991

Purification and partial characterization of ubiquitin-activating enzyme from Saccharomyces cerevisiae.

Ubiquitin-activating enzyme was purified from the yeast Saccharomyces cerevisiae by covalent affinity chromatography on ubiquitin-Sepharose followed by HPLC anion-exchange chromatography. Enzyme activity was monitored by the ubiquitin-dependent ATP: 32PPi exchange assay. The purified enzyme has a specific activity of 1.5 mumol 32PPi incorporated into ATP.min-1.mg-1 at 37 degrees C and pH 7.0 under standard conditions for substrate concentrations as described by Ciechanover et al. (1982) J. Biol. Chem. 257, 2537-2542. The catalytic activity showed a maximum at pH 7.0. Its molecular weight both in non-denaturing and in SDS-gel electrophoresis was estimated to be 115 kDa, suggesting a monomeric form. The isoelectric point determined by gel electrofocusing was approximately 4.7. Two protein bands differing slightly in electrophoretic mobility could be distinguished when SDS gels were loaded with very small amounts of purified E1 and immunoblotted, the one with higher molecular weight being clearly predominant. The same two bands were also found in anti-E1 immunoblots of crude yeast lysates prepared under broad protease inhibition.

Blotting, Western↗
PubMed1991

Immunocytochemical localization of ubiquitin-activating enzyme in the cell nucleus.

Ubiquitin-activating enzyme, "E1", is the first enzyme in the pathway leading to formation of ubiquitin-protein conjugates. We present immunocytochemical evidence that Ubiquitin-activating enzyme is concentrated in the cell nucleus. This finding points to the nucleus as the major site of action of this enzyme. Since ubiquitin itself is not similarly compartmentalized, this result suggests a high level of ubiquitin conjugate formation in the nucleus with a rapid turnover of ubiquitin conjugates.

Animals↗
PubMed1991

Collagen remodeling and changes in LV function during development and recovery from supraventricular tachycardia.

Chronic supraventricular tachycardia (SVT) causes left ventricular (LV) dYsfunction and dilatation. Termination of SVT appears to improve symptoms of congestive heart failure. However, the structural events that occur during development and regression of SVT-induced cardiomyopathy are unknown. Accordingly, LV function (simultaneous echocardiogram-catheterization) and collagen content and distribution were measured in pigs (23-25 kg) assigned to three groups: 1) rapid atrial pacing (240 beats/min) for 3 wk (SVT, n = 10); 2) SVT for 3 wk, followed by deactivation of the pacemaker and a 4-wk recovery period (PST, n = 9); and 3) sham-operated controls (CON, n = 10). LV fractional shortening was 30 +/- 2% in CON, fell to 13 +/- 2% with SVT (P less than 0.05), and returned to CON values with PST (31 +/- 2%). SVT resulted in significantly increased LV end-diastolic dimension compared with CON (4.9 +/- 0.3 vs. 3.5 +/- 0.2 cm, P less than 0.05) and no change in LV wt/body wt (2.7 +/- 0.2 vs. 2.6 +/- 0.2 g/kg, P = 0.85). Termination of SVT (PST) resulted in development of hypertrophy, LV mass increased to 3.50 +/- 0.3 g/kg (P less than 0.05 vs. CON). With the use of pressure-dimension-thickness relations during diastole, the regional chamber stiffness constant (Kc) was computed. Kc was unchanged by SVT compared with CON (5.3 +/- 1.4 vs. 3.7 +/- 0.5, P greater than 0.35) but increased with PST (7.4 +/- 0.6, P less than 0.05). LV hydroxyproline content significantly fell with SVT compared with CON (2.24 +/- 0.58 vs. 2.68 +/- 0.45 mg/g dry wt, P less than 0.05, respectively) and significantly increased with PST (3.68 +/- 0.85 mg/g dry wt, P less than 0.05). With the use of transmission electron microscopy, collagen fibril diameter was reduced with SVT compared with CON (1.45 +/- 0.5 vs. 1.7 +/- 0.5 microns, P less than 0.05) and increased with PST (3.3 +/- 1.4 microns, P less than 0.05). Scanning electron microscopy revealed disruption of collagen struts between adjacent SVT myocytes and a thickened collagen weave with PST. Thus chronic SVT resulted in systolic and diastolic dysfunction and reduced collagen support of adjoining myocytes. Early recovery from SVT was associated with LV hypertrophy, increased collagen, and increased LV stiffness.

Animals↗
PubMed1990

Creatine kinase: race-gender differences in patients hospitalized for suspected myocardial infarction.

Race-gender differences in creatine kinase values were studied in 647 consecutive patients admitted for suspected myocardial infarction. The lowest value in a serial set for each patient was used for group comparisons. Significant differences were found between Hispanic females and black males, using standard values. Using log creatine kinase values, significant differences were found among blacks, Caucasians, and Hispanics. Males had higher log creatine kinase values than females, but no differences were found between sexes within racial groups. Body surface area differences (significant between males and females) did not explain all of the racial-gender differences found. Reexamination of ranges of normality, taking into account race-gender differences, is strongly supported by these data.

Asian People↗
PubMed1989

Characterization of a specific binding protein for 2,3,7,8-tetrachlorodibenzo-p-dioxin in human thymic epithelial cells.

Specific toxic and biochemical responses elicited by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in human thymic epithelial (TE) cells in culture are mediated by the TCDD receptor protein. Characterization of the physicochemical properties of the TCDD receptor in cytosol fractions from cultured human TE cells indicates that this protein is similar, but not identical, to the extensively studied receptor species present in mouse and rat liver. The human TCDD receptor sediments at 9.1 S on sucrose density gradients at 0 degrees, undergoes a temperature-dependent conversion at 20 degrees to a species sedimenting at 10.7 S, and partially dissociates in the presence of 0.4 M KCl, as judged by the appearance of a peak sedimenting at 5 S. Both the temperature- and salt-dependent changes in the observed physical properties of the human TCDD receptor are inhibited by sodium molybdate. Two molybdate-stabilized binding species can be resolved from TCDD specific binding isotherms to human TE cytosol. Under identical conditions, only a single TCDD specific binding component was detected in cytosol fractions from both mouse and rat liver. Mixing cytosol prepared from human TE cells with hepatic cytosol fractions from C57BL/6 mice revealed the presence of a heat-labile, trypsin-sensitive factor in human TE cells that inhibits TCDD specific binding to the murine hepatic receptor. Molybdate stabilized the mouse receptor against the actions of this human inhibitory factor. Molybdate also may stabilize the human TCDD receptor, as indicated by the 2- to 3-fold increase in total TCDD specific binding measured in human TE cytosol fractions in the presence of this metallo-oxyanion.

Adolescent↗
PubMed1987

An in vitro model for studying the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin to human thymus.

A coculture system of human thymic epithelial (HuTE) cells and thymocytes (T lymphocyte precursors) has been established and characterized as an in vitro model for assessing the potential toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to human thymus. HuTE cells in culture were responsive to TCDD as judged by induction of the cytochrome P1-450 monooxygenase activities, 7-ethoxycoumarin O-deethylase (ECOD) and 7-ethoxyresorufin O-deethylase (EROD). Measurement of the responsiveness of thymocytes cocultured on TCDD-pretreated HuTE monolayers to the mitogens concanavalin A (Con A) and phytohemagglutinin (PHA) indicated that TCDD can act directly on HuTE cells to suppress thymocyte maturation (at a concentration of 10 nM, TCDD produced a 25 to 50% inhibition of thymocyte responsiveness to Con A and PHA). Both the induction of cytochrome P1-450 monooxygenase activity (EC50 values approximately 1 nM) and immunosuppressive responses elicited by TCDD in HuTE cells were concentration-dependent and stereospecific (as judged by the relative activities of chlorinated dibenzo-p-dioxin and dibenzofuran isomers), indicating involvement of the Ah receptor which was detected in all HuTE strains examined. Initial characterization of these Ah receptor-mediated responses in several strains of HuTE cells indicated marked interstrain differences in maximally inducible ECOD and EROD activities which did not appear to directly correlate with measured concentrations of the cytosolic Ah receptor, and in certain strains examined, differences in sensitivity and magnitude were observed for TCDD-evoked immunotoxic responses but not always for the induction response. These data on the actions of TCDD on cultured HuTE cells suggest that human thymus is a target for TCDD and related halogenated aromatic compounds. In HuTE cells, measurement of either the Ah receptor concentration or of marker responses such as the induction of cytochrome P1-450 alone cannot provide an accurate quantitative assessment of susceptibility to TCDD-induced thymus toxicity.

7-Alkoxycoumarin O-Dealkylase↗