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Biomedical subjects

J C Cook

Publications and source records attributed to J C Cook.

90 records · Page 5Linked to original sources
PubMed1977

Phosphazenes: high molecular weight reference compounds for field desorption mass spectrometry.

Because of poor field ionization sensitivity or an insufficient number of peaks, conventional reference materials are inadequate for field desorption mass spectrometry. Hexakis (multifluoroalkoxy)cyclotriphosphazenes satisfy a growing need for high molecular weight reference compounds amenable to either electron impact or field ionization. In comparison with tris(perfluoroalkyl)-s-triazine standards, the substituted phosphazenes offer greater volatility, easier synthesis and better mass spectral characteristics. Phosphazene mixtures, in particular, cover a broad mass range in either ionization mode, creating new measurement capabilities for ions at high masses.

Chromatography, Gas↗
PubMedDate not supplied

The induction of cytochrome P-450 by isosafrole and related methylenedioxyphenyl compounds.

Using sucrose gradients, the Ah receptor and a 3-4S binding peak were measured in hepatic cytosol from Dub: ICR, C57BL/6, and DBA/2 male mice. Isosafrole, piperonyl butoxide, and 5-t-butyl-1,3-benzodioxole were unable to displace 2,3,7,8-tetrachlorodibenzo-p-dioxin or 3-methylcholanthrene from either the Ah receptor or the 3-4S binding peak, in vitro. In in vivo experiments, treatment of C57BL/6 mice with 3-methylcholanthrene caused a 4-fold reduction in Ah receptor binding 2 h after i.p. injection; whereas, isosafrole caused a 2-fold enhancement of the Ah receptor after 24 h. This increase in the Ah receptor binding following isosafrole treatment may be due to induction. 3-Methylcholanthrene treatment of C57BL/6 mice also caused a 3-fold reduction in the 3-4S binding peak 2 h after i.p. injection; isosafrole treatment had little or no effect on the 3-4S peak in C57BL/6 or DBA/2 mice. Both in vivo and in vitro data appear to demonstrate that there is no direct role for the Ah receptor or the 3-4S protein in the regulation of cytochrome P-450 by methylenedioxyphenyl compounds. Using Sephadex G-100 chromatography, a cytosolic protein fraction was obtained from C57BL/6 and Dub:ICR mice which was previously implicated by others as a carrier in the metabolism of benzo[a]pyrene (B[a]P). This fraction was applied to sucrose gradients and sedimented in the 3-4S region. Hence it appears that the 3-4S binding peak may be the carrier described by these workers.

Animals↗
PubMedDate not supplied

Detection of dopaminergic modulators in a tier I screening battery for identifying endocrine-active compounds (EACs).

Apomorphine (APO; D(2) receptor agonist), haloperidol (HAL; D(2) receptor antagonist), and reserpine (RES; a dopamine depletor that acts to lower brain dopamine levels by depleting central nervous system monoamines via disrupting storage vesicle function) have been examined in a Tier I screening battery, which has been designed to detect endocrine-active compounds (EACs). The Tier I battery incorporates two short-term in vivo tests (a 5-day ovariectomized female battery and a 15-day intact male battery using Sprague-Dawley rats) and an in vitro yeast transactivation system (YTS). In addition, two blood collection procedures were evaluated for their utility in detecting HAL-induced increases in serum prolactin (PRL) levels (i.e., the stress associated with each procedure). In the in vivo female battery, both HAL and RES increased serum PRL concentrations as expected, although the increase caused by RES was marginal. Increases in serum PRL levels are enhanced when daily dosages are administered via multiple-daily dosing of the test compound, which results in higher sustained blood levels of the test compounds. APO failed to decrease serum PRL concentrations in the female battery. In the in vivo male battery, HAL increased serum PRL concentrations as expected. However, APO and RES failed to affect serum PRL concentrations. The blood collection comparison experiment demonstrated that possible confounding of the data can occur with serum PRL concentrations when animals are exposed to stress. Basal levels of PRL were approximately fourfold higher in animals that were bled via the tail vein procedure when compared to PRL levels from animals that were bled under CO(2) anesthesia at euthanization. As a result of the higher basal PRL levels, the HAL-induced increase in serum PRL concentrations was completely attenuated in the tail-vein bled animals (1.3-fold). In contrast, HAL produced a fivefold increase in serum PRL in animals where blood was collected under CO(2) anesthesia at euthanization. Hence, collection of blood from animals under CO(2) anesthesia at euthanization is an acceptable approach for detection of compounds that increase PRL. In summary, HAL-like compounds would be identified in the Tier I male and female battery primarily via increased serum PRL concentrations. RES-like compounds would be identified in the Tier I male battery via decreased gonadotropins and steroids and possibly in the Tier I female battery by a minimal increase in serum PRL concentrations. Compounds that produce a marginal increase in serum PRL when administered using single daily dosing can also be confirmed in an in vivo female battery with multiple dosing because this regimen increases the magnitude of the PRL increase. APO, a D(2) receptor agonist, was not detected in the in vivo male or female batteries, but in both instances the top dosage produced minimal decreases in body weight (99 to 96% of control). Hence, the proposed Tier I battery needs to be further evaluated with higher dosages of APO and other D(2) receptor agonists to determine whether it is capable of detecting such agents.

Androgens↗
PubMedDate not supplied

Weak estrogenic activity from continuous-release pellets.

In the process of evaluating a proprietary compound for weak estrogenic activity, two different types of dosing regimens were used, repeated daily dosing (three times/d) and continuous-release pellets. In studies using the proprietary compound, rats that were dosed via intraperitoneal injection showed no estrogenic responses, while those receiving the test compound via continuous-release pellets displayed several estrogenic responses. Because of the conflicting results, the control pellets were evaluated for estrogenic activity in the same battery of tests using the same number of pellets. In studies using only the control pellets, several estrogenic responses were observed including increased uterine weight, uterine stromal cell proliferation, estrous conversion, uterine progesterone receptor content, and decreased uterine estrogen receptor content. Animals receiving no pellet implant showed no estrogenic responses. In addition, a methylene chloride/DMSO extract of the control pellets promoted expression of a reporter gene controlled by the estrogen receptor and demonstrated competition with 17 beta-estradiol for binding to the human estrogen receptor. It is concluded that component(s) of the control pellets possess weak estrogenic activity.

Animals↗
PubMedDate not supplied

Leydig cell hyperplasia and adenoma formation: mechanisms and relevance to humans.

Leydig cell adenomas are observed frequently in studies evaluating the chronic toxicity of chemical agents in laboratory animals. Doubts have been raised about the relevance of such responses for human risk assessment, but the question of relevance has not been evaluated and presented in a comprehensive manner by a broad group of experts. This article reports the consensus conclusions from a workshop on rodent Leydig cell adenomas and human relevance. Five aspects of Leydig cell biology and toxicology were discussed: 1) control of Leydig cell proliferation; 2) mechanisms of toxicant-induced Leydig cell hyperplasia and tumorigenesis; 3) pathology of Leydig cell adenomas; 4) epidemiology of Leydig cell adenomas; and 5) risk assessment for Leydig cell tumorigens. Important research needs also were identified. Uncertainty exists about the true incidence of Leydig cell adenomas in men, although apparent incidence is rare and restricted primarily to white males. Also, surveillance databases for specific therapeutic agents as well as nicotine and lactose that have induced Leydig cell hyperplasia or adenoma in test species have detected no increased incidence in humans. Because uncertainties exist about the true incidence in humans, induction of Leydig cell adenomas in test species may be of concern under some conditions. Occurrence of Leydig cell hyperplasia alone in test species after lifetime exposure to a chemical does not constitute a cause for concern in a risk assessment for carcinogenic potential, but early occurrence may indicate a need for additional testing. Occurrence of Leydig cell adenomas in test species is of potential concern as both a carcinogenic and reproductive effect if the mode of induction and potential exposures cannot be ruled out as relevant for humans. The workgroup focused on seven hormonal modes of induction of which two, GnRH agonism and dopamine agonism, were considered not relevant to humans. Androgen receptor antagonism, 5 alpha-reductase inhibition, testosterone biosynthesis inhibition, aromatase inhibition, and estrogen agonism were considered to be relevant or potentially relevant, but quantitative differences may exist across species, with rodents being more sensitive. A margin of exposure (MOE; the ratio of the lowest exposure associated with toxicity to the human exposure level) approach should be used for compounds causing Leydig cell adenoma by a hormonal mode that is relevant to humans. For agents that are positive for mutagenicity, the decision regarding a MOE or linear extrapolation approach should be made on a case-by-case basis. In the absence of information about mode of induction, it is necessary to utilize default assumptions, including linear behavior below the observable range. All of the evidence should be weighed in the decision-making process.

Adenoma↗
PubMedDate not supplied

Evidence that nitric oxide enhances cadmium toxicity by displacing the metal from metallothionein.

Cadmium is carcinogenic in humans and rodents. Although extensive evidence indicates that the toxicity and genotoxicity of Cd is ameliorated by binding to cysteine clusters in metallothionein (MT), the factors governing Cd release at intracellular target sites remain unknown. Nitric oxide is a pollutant gas and an important intercellular messenger in the inflammatory immune response. When growing Chinese hamster ovary cells were treated for 24 h with 0.5, 0.75, or 1.0 mM CdCl2 followed by a 1-h exposure to 1.0, 1.5, or 2.0 mM 1,1-diethyl-2-hydroxy-2-nitrosohydrazine (DEA/NO), an NO-generating sodium salt, NO enhanced Cd-induced inhibition of colony forming ability without affecting Cd-induced cytolethality. In experiments designed to determine whether NO acts by displacing Cd from cellular MT, cells treated with 2.0 mM CdCl2 followed by 1.5 or 3.0 mM DEA/NO exhibited 29 and 38% reductions, respectively, in the amount of Cd bound to MT. When purified rat liver MT was used to further characterize NO-induced release of Cd from MT, dose-related increases in Cd displacement were observed at DEA/NO concentrations between 0.1 and 0.5 mM, and a plateau was reached at 3 mol of Cd displaced/mol of MT at higher DEA/NO concentrations. Compared to cells exposed to Cd or DEA/NO alone, cells treated with Cd followed by DEA/NO also exhibited a transient 2-3-fold decrease in c-myc proto-oncogene expression. Taken together, our results support the hypothesis that NO mediates Cd release from MT in vivo and suggest that intracellular generation of free Cd may induce DNA damage and force cells into a period of growth arrest. Such findings may have particular relevance with regard to the etiology of Cd-induced carcinogenesis in human populations.

Animals↗
PubMedDate not supplied

Induction of coagulation effects by Wyeth-14,643 in Crl:CD BR rats.

A two-year mechanistic bioassay in male Crl:CD BR rats was initiated with 50 ppm Wyeth-14,643 (WY) to investigate the relationship between peroxisome proliferating compounds and Leydig cell adenoma formation. After 154 days, the survival rate in the WY group decreased below control levels. After 300 days, the dose was lowered to 25 ppm for the remainder of the study. Gross examination of WY-treated rats either found dead or euthanized in extremis revealed hemorrhages at several sites. To investigate this observation, blood was then collected on test day 281 from 10 randomly selected control and WY-treated rats and a clinical pathological examination was performed. The WY-treated rats had significantly decreased red blood cell count, hemoglobin, and hematocrit, and elevated platelet counts. In the WY-treated rats, prothrombin times in undiluted plasma were similar to the controls, but were markedly prolonged in 2 of 10 rats when the plasma samples were diluted to 25%. Subsequently, blood was collected prior to sacrificing WY-treated rats which were exhibiting clinical signs of anemia. These rats had prolonged prothrombin times, activated partial thromboplastin time, and thrombin clot time when compared to laboratory historical control data (116.7 vs 13.3, 116.4 vs 13.7, and 42.4 vs 25.7 seconds, respectively). In a subsequent, ongoing study, Vitamin K was added to control and WY-treated diets (100 ppm). No survival differences between control and WY-treated rats occurred through 260 days in this second study. These new data suggest that deaths in the WY-treated group in our initial study were due to a vitamin K deficiency. The role of increased serum estradiol, its effects on blood coagulation, and enhanced hepatic cell proliferation in the vitamin K-dependent coagulation processes warrant further investigation.

Analysis of Variance↗