Biomedical subjects

C A Snyder

Publications and source records attributed to C A Snyder.

At least 37 records · Page 2Linked to original sources

PubMed1991

Detection of cadmium exposure in rats by induction of lymphocyte metallothionein gene expression.

The induction of metallothionein (MT) gene expression in lymphocytes of rats was determined in order to detect exposure in vivo to cadmium. Both acute and chronic CdCl2 exposures resulted in the induction of the MT-1 gene in lymphocytes as measured by standard RNA Northern blot analysis. Twenty-four hours following an ip injection of 3.4 mg/kg CdCl2, a ninefold increase in MT gene expression was observed in lymphocytes, as well as five- and sevenfold increases in liver and kidney, respectively. Oral exposure of rats to 1-100 ppm CdCl2 via drinking water resulted in an approximate twofold enhanced MT signal in lymphocytes after 6 wk, and a threefold increase after 13 wk of exposure to 100 ppm Cd. No increases in lymphocyte MT gene expression were observed after 3 wk of Cd exposure. Liver MT gene expression was substantially induced following chronic Cd exposure, while kidney was not, although this organ had a higher basal expression of the MT-1 gene. Analysis of tissue Cd burdens demonstrated a dose-response Cd accumulation in liver and kidney, but only kidney burdens increased substantially with prolonged Cd exposure. These results demonstrate the utility of lymphocyte gene expression assays to detect in vivo toxicant exposure, and thus their applicability as molecular biomarker assays for human exposure assessment.

Animals↗

PubMed1991

Lymphocyte proliferation assays as potential biomarkers for toxicant exposures.

Recently there has been interest in developing assays that can be used as indicators (biomarkers) of exposure to toxic agents. We have been exploring the potential utility of three lymphocyte proliferation assays [the responses of B lymphocytes to the mitogen lipopolysaccharide (LPS), the responses of T lymphocytes to the mitogen concanavalin A (ConA), and the responses of T lymphocytes to antigenic stimuli in a mixed lymphocyte culture (MLC) assay] as biomarkers of toxicant exposure. Studies were initiated to assess the applicability and specificity of these assays and to investigate the mechanisms by which toxicants alter lymphocyte proliferation. All studies were performed using cells isolated from Fischer 344 rats. To assess applicability, mitogen assays were performed using in vitro exposures to eight different toxicants: hydroquinone, benzoquinone, Aroclor 1254, styrene oxide, and the salts of mercury, cadmium, chromate, and nickel. In vitro concentrations spanned five orders of magnitude (100 to 0.01 mg/l). At the lowest concentration tested, all eight compounds induced changes in at least one mitogen assay, indicating that these assays may be applicable to a wide range of toxicants. Variations of the ConA and MLC assays were used to test for specificity. In both assays, splenocytes taken from rats exposed in vivo to either chromate or to cadmium responded differently when the cells were cocultured with exogenously added chromate or cadmium ions, indicating that it may be possible to detect exposure to a specific toxicant by performing modified lymphocyte proliferation assays. In the mechanistic studies, splenocytes from cadmium and chromate-treated rats altered the ConA-induced proliferation of cocultured syngeneic cells. In addition, the antigenicity of splenocytes isolated from cadmium-treated rats was enhanced when these cells were used as stimulators for allogeneic splenocytes. The results of these studies indicate that lymphocyte proliferation assays may be useful for detecting exposure to a wide range of toxicants and that variations of these assays may be useful for implementing immunologically based tests for detecting exposures to specific chemicals.

Animals↗

PubMed1991

Immune function assays as indicators of chromate exposure.

The potential immunomodulatory effects of chromium were investigated using a series of in vitro and in vivo studies. Chromium (as K2CrO4) in concentrations spanning five orders of magnitude was added in vitro to T-lymphocyte (concanavalin A) and B-lymphocyte (liposaccharide) mitogen cultures and was found to inhibit T-lymphocyte responses at all concentrations tested and to inhibit B-lymphocyte responses at all but the lowest concentration tested (0.01 mg/L). When the same concentrations of chromium were employed in mixed lymphocyte cultures, antigen-induced thymidine uptake was inhibited at the highest concentrations (100 mg/L-1 mg/L), enhanced at 0.1 mg/L, and equal to control values at lower concentrations. Splenocytes isolated from rats exposed to K2CrO4 in drinking water exhibited enhanced responses to T- and B-lymphocyte mitogens. The addition of 0.1 mg/L of chromium to a mixed lymphocyte culture containing splenocytes taken from chromium-exposed rats increased by 5-fold the uptake of thymidine by these cells. These increased responses of cells from chromium-exposed rats may indicate chromium-induced sensitization and may possibly be used as a biological marker for chromium exposure.

Animals↗

PubMed1990

Short term benzene exposure provides a growth advantage for granulopoietic progenitor cells over erythroid progenitor cells.

Because chronic benzene exposure is associated with acute myeloblastic leukemia and other myeloproliferative disorders, we sought to determine whether short-term benzene exposure provides a growth advantage for granulopoietic elements over erythropoietic elements. Groups of male DBA/2J mice were exposed to 0, 10, 30, or 100 ppm benzene (6 h/day for 5 days). One day and 5 days after the benzene exposures, the numbers of the two most primitive erythroid progenitor cells (BFU-E and CFU-E) and the numbers of the most primitive granulocytic progenitor cells (GM-CFU-C) were assessed. Additional groups of mice were given hemolytic doses of phenylhydrazine (PHZ) during the 5 days of benzene exposure, while other groups of mice were given PHZ during the 5 days of recovery from benzene exposure. These experiments were designed to determine the effects of benzene exposure on progenitor cell numbers during periods of markedly heightened erythropoiesis. The results demonstrate that short-term benzene exposure does induce a growth advantage for granulocytic cells in both the bone marrow and spleen of exposed mice. Moreover, a benzene-induced shift toward granulopoiesis is observed even in those mice treated with a powerful erythropoietic stimulus. These effects disappear 5 days after cessation of benzene exposure in the bone marrow but persist in the spleen of mice treated with phenylhydrazine.

Animals↗

PubMed1989

The ability of the murine erythron to respond to hemolytic doses of phenylhydrazine is significantly impaired by exposures to 10 ppm benzene.

Male C57Bl mice were given 50 exposures (6 h/d x 5 d/wk x 10 wk) to 10 ppm benzene. At regular intervals during the course of the exposures, the numbers of erythroid colony-forming cells (CFU-E) and the numbers of granulocytic colony-forming cells (GM-CFU-C) were assayed. At the end of the benzene exposures, additional groups of mice were given 4 daily injections of phenylhydrazine (PHZ) to induce anemia. During the course of the exposures, the numbers of colony-forming cells from benzene-exposed mice were, with infrequent exceptions, statistically indistinguishable from the numbers of these cells in air-exposed mice. However, in response to the PHZ-induced anemia, the numbers of late erythroid (CFU-E) and granulocytic (GM-CFU-C) progenitor cells were about 30% lower among benzene-exposed mice than among air-exposed mice. These results suggest that concentrations of benzene that induce little or no observable hematopoietic changes may, in fact, greatly alter the hematopoietic capacity of an exposed individual.

Anemia, Hemolytic↗

PubMed1989

The neuroendocrine system, an opportunity for immunotoxicologists.

The interrelationship between the neuroendocrine and immune systems was first recognized over 50 years ago. Subsequent investigations have shown that gene products produced by the neuroendocrine system affect the activities of immunologically competent cells. More recent data show that cells of the two systems possess receptors that are identical. Because of these strong interrelationships, it is postulated that compounds that affect the neuroendocrine system will also affect the immune system. It follows that the readily accessible cells of the immune system can be used as surrogates for the less accessible cells of the neuroendocrine system. Moreover, the assays typically used by immunotoxicologists could provide quantitative information regarding dose response, persistence of effects, and surveillance of the extent of exposure for compounds known to be neurotoxicants. Thus, much useful information could be acquired by applying the technique of immunotoxicology to the study of neurotoxicants.

Animals↗

PubMed1989

Mutagenic metabolites of benzene detected in the Microscreen assay.

The reactive metobolite responsible for benzene hematotoxicity and carcinogenicity is unknown. It can be hypothesized that the ultimate carcinogen derived from benzene metabolism might also act as a mutagen. This laboratory has recently developed a new assay that can detect mutagens of all types, using a single strain of bacteria, E. coli WP2s (lambda), as a target. Different genetic end points can be monitored in the same exposed population of bacteria. When a number of known metabolites of benzene were assayed, only trans,trans-muconic acid gave a strong positive response. Mutations were induced at two genetic loci (Trp+ revertants and T5 resistance). The mutagenic activity was greatly increased when a rat liver metabolizing system was added. We speculate that trans,trans-muconic acid is metabolized to a diepoxide, which may be the ultimate mutagen and possibly the ultimate carcinogen.

Animals↗

PubMed1988

The carcinogenicity of discontinuous inhaled benzene exposures in CD-1 and C57Bl/6 mice.

Groups of male C57Bl and CD-1 mice were exposed to benzene via inhalation using two different exposure protocols. One protocol consisted of repetitive week-long exposures to 300 ppm benzene (6 h/d x 5 d/wk) interrupted by 2 weeks of non-exposure. The exposure pattern (1 week of exposure followed by 2 weeks of non-exposure) was continued until the death of the last exposed animal. The second protocol consisted of exposures to 1200 ppm benzene (6 h/d x 5 d/wk) for 10 weeks. Exposures were then terminated and the animals allowed to live out their lives. For each protocol, appropriate age-matched control mice received comparable exposures to filtered, conditioned air. The discontinuous exposure patterns mimic the patterns of exposure often encountered in the workplace and, in addition, prolong the survival of exposed animals so as to maximize potential tumorigenic responses. Both exposure protocols were markedly hematotoxic to both mouse strains as measured by peripheral blood counts. Both strains of mice responded to the intermittent 300 ppm benzene exposures with elevated incidences of malignant tumors. Particularly noteworthy was a 35% incidence of zymbal gland tumors in the C57Bl mice. In contrast, only the CD-1 mice responded to the 1200 ppm benzene exposures delivered over 10 weeks with elevated tumor incidences. A 46% incidence of lung adenoma was particularly striking in these mice. Neither of the benzene exposure protocols induced elevated incidences of leukemia/lymphoma in either strain.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗

PubMed1988

"Crack smoke" is a respirable aerosol of cocaine base.

The smoking of cocaine base [corrected] ("crack") has emerged as a significant substance abuse problem. A detailed characterization of cocaine smoke is a prerequisite for studies of its pharmacokinetics, abuse potential and toxicity. Model pipes were used to generate cocaine smoke analogous to that inhaled by human "crack" abusers. Using procedures to minimize pyrolysis, cocaine base smoke was determined to be 93.5% cocaine particles with the remainder being cocaine vapor. The average particle size generated from all model pipes was 2.3 mu which is small enough to ensure deposition into the alveolar region of the human lung. Although this particle size is eminently respirable [corrected] by primates, a much smaller fraction will reach the alveolar region of rodents. Special generating procedures would therefore be required to expose rodents to meaningful doses of airborne cocaine that mimic the rapid absorption achieved by "crack" smokers.

Aerosols↗

PubMed1988

Mice exposed in utero to 20 ppm benzene exhibit altered numbers of recognizable hematopoietic cells up to seven weeks after exposure.

Pregnant Swiss Webster mice were exposed from Day 6 through Day 15 of gestation to either air, 5 ppm, 10 ppm, or 20 ppm benzene. On Day 16 of gestation, 2 days after birth, and 6 weeks after birth, progeny of the exposed dams were assayed for the amount and type of hemoglobin produced and for recognizable hematopoietic cells in the peripheral blood and hematopoietic organs. None of the benzene exposures induced significant changes in the indices assayed from the 16-day fetuses. In contrast, 2-day neonates exposed in utero to all concentrations of benzene exhibited reduced numbers of circulating erythroid percursor cells. In addition, those 2-day neonates exposed in utero to 20 ppm benzene exhibited increased numbers of hepatic hematopoietic blast cells and granulopoietic precursor cells accompanied by decreased numbers of erythropoietic precursor cells. Six-week adult mice exposed in utero to 20 ppm benzene exhibited a similar pattern of enhanced granulopoiesis. These animals exhibited elevated numbers of splenic hematopoietic blast cells and granulopoietic precursor cells accompanied by decreased numbers of marrow erythropoietic precursor cells. These results suggest that in utero exposures to low concentrations of benzene can induce persistent enhanced production of recognizable granulopoietic elements in the hematopoietic systems of mice.

Animals↗

PubMed1988

Prolonged red blood cell glycerol hemolysis in mice inhaling benzene.

Inhalation of benzene produces a prolongation of mouse red blood cell glycerol hemolysis time. This was not observed in red blood cells directly incubated in benzene. Increased resistance to the hemolytic action of glycerol should be explored as a potentially useful biological monitoring procedure in the red blood cells of benzene-exposed humans.

Animals↗

PubMed1987

Inhaled benzene reduces aspects of cell-mediated tumor surveillance in mice.

Benzene is a potent bone marrow toxicant with particular activity against lymphocytes. Despite the recognized effects of benzene on lymphocyte populations, few data exist concerning the effects of benzene on in vivo immune responses. We have been conducting a series of studies concerning the effects of inhaled benzene on murine cell-mediated immune responses. The studies in this report involve the interaction of inhaled benzene with some of those cell-mediated immune responses associated with tumor surveillance. Exposures to 100 ppm benzene (5 days/week X 20 weeks) induced lethal tumor growth in 9/10 C57Bl/6 mice inoculated with 10(4) viable PYB6 tumor cells. Lethal tumor incidences in air controls and mice exposed to lower benzene concentrations were 3/10 or less. Exposures to 100 ppm benzene (5 days/week X 4 weeks) also reduced the tumor lytic abilities of cytotoxic T lymphocytes as determined by 51Cr-release assays. In addition, splenocytes taken from mice exposed to 10 or 100 ppm benzene (5 days/week X 4 weeks) exhibited delays in peak mixed leukocyte responses. Coculture experiments demonstrated that these delays were not due to an induction of suppressor cell activity by benzene. There were no alterations in the relative percentages of B cells, T cells, or T-cell subsets among splenocytes from animals exposed to any concentration of benzene tested. These results demonstrate that inhaled benzene can inhibit some of the processes associated with tumor surveillance, and that this inhibition is due, at least in part, to impairments of the functional abilities of some of the cells responsible for tumor surveillance.

Administration, Inhalation↗

PubMed1987

A new inhalation exposure system for the determination of inhaled doses in laboratory rats.

A new inhalation exposure system has been developed which allows the determination of inhaled doses of vapors and gases by laboratory rats. The system consists of saran bags connected to head-only exposure cylinders via one-way valves. One bag serves as the source of contaminant and another receives expired air. The exposure cylinders also serve as whole body plethysmographs. Up to three rats can be exposed concurrently to the same concentration of test material. The construction of the system and its use for inhalation exposures to a direct-acting radiolabeled carcinogen are described.

Administration, Inhalation↗

PubMed1987

Isopropyl methanesulfonate is a potent red cell hematotoxicant.

Mice given 10-weekly injections (i.m.) of 20 mumol of isopropyl methanesulfonate (IPMS) in trioctanoin exhibited depressed hematopoiesis as manifested by reduced peripheral blood counts and by reduced thymic and bone marrow cellularities. The treatments were particularly toxic to erythroid populations and ultimately induced signs of splenic erythropoiesis. Bone marrow cellularity recovered during the latter stages of the treatments indicating that subpopulations of hematopoietic cells were resistant to the treatments. This recovery of bone marrow cellularity may bear on the recently discovered leukemogenic potential of IPMS.

Animals↗

PubMed1987

Inhalation carcinogenesis of various alkylating agents.

A series of earlier studies showed that inhalation exposures of rats to three water-reactive electrophilic compounds produced brisk yields of nasal cancer even when the animals were exposed for only 30 days (6 hr/day X 5 day/wk). In addition, carcinogenic potencies of the compounds appeared to relate to their chemical reactivities as measured by hydrolysis rates. For a further study of this phenomenon, inhalation exposures were conducted with five additional water-reactive compounds: beta-propiolactone [(BPL) CAS: 57-57-8], methylmethane sulfonate [(MMS) CAS: 66-27-3], ethylchloroformate [(ECF) CAS: 541-41-3], dichloroacetyl chloride [(DCAC) CAS: 79-36-7], and propylene oxide [(PO) CAS: 75-56-9] on male Sprague-Dawley rats. The hydrolysis rates of these compounds span 6 orders of magnitude. The compounds were administered for 30 days (6 hr/day X 5 days/wk) with the use of exposure concentrations that were inversely proportional to the respective hydrolysis rates. With this protocol, all compounds except PO (the slowest reacting compound) produced nasal cancer in rats. The concentrations of MMS and BPL employed in the studies produced similar nasal cancer yields, indicating that the carcinogenic potencies of these compounds in rat nasal mucosa were proportional to their hydrolysis rates. The nasal cancer yields of DCAC and ECF were less than expected. DCAC hydrolyzes so rapidly at in vivo temperatures (half-life much less than 0.01 min) that it may not reach target DNA in reactive form. Why the exposures to ECF produced yields of nasal cancer not predicted by its reactivity is currently under investigation. These results combined with our earlier results demonstrate that the carcinogenic potencies of some inhaled reactive electrophilic compounds are related to their hydrolysis rates.

Acetates↗

PubMed1986

Mice exposed in utero to low concentrations of benzene exhibit enduring changes in their colony forming hematopoietic cells.

Pregnant Swiss-Webster mice were exposed to either 0, 5, 10, or 20 ppm benzene from days 6 through 15 of gestation. Hematopoietic progenitor cell assays were performed on fetal, neonatal and adult progeny of the exposed dams. All concentrations of benzene employed induced marked changes in the numbers of the more differentiated erythroid colony forming cells, the CFU-E. Granulocytic colony forming cells (GM-CFU-C) were affected by the 2 higher exposure concentrations. When mice previously exposed in utero to 10 ppm benzene were re-exposed as adults, marked depressions in the numbers of CFU-E and GM-CFU-C were observed. Thus, in utero exposures to concentrations of benzene at the current occupational exposure limit induce alterations of the murine hematopoietic system which persist into adulthood.

Administration, Inhalation↗

PubMed1986

Relationships between the levels of binding to DNA and the carcinogenic potencies in rat nasal mucosa for three alkylating agents.

Three direct-acting carcinogens, beta-propiolactone (BPL), methylmethane sulfonate (MMS), and dimethylcarbamyl chloride (DMCC), were evaluated for their carcinogenic potencies in the nasal mucosa of rats and for their abilities to bind in vivo to rat nasal mucosal DNA. The relative carcinogenic potencies of BPL and MMS corresponded well with their overall levels of binding to nasal mucosal DNA. DMCC, however, the most potent carcinogen of the three compounds, produced the lowest level of binding to nasal mucosal DNA. These results indicate that the DNA adducts formed by DMCC in rat nasal mucosa DNA are more readily expressed as cancer than those formed by BPL or MMS.

Alkylating Agents↗

PubMed1985

Modulation of the immune response to Listeria monocytogenes by benzene inhalation.

Benzene is a potent bone marrow toxicant. While all blood cell types are targets for benzene poisoning, lymphocytes are particularly sensitive. The immunotoxic consequences of benzene or its metabolites have been demonstrated in a number of in vitro studies; however, little data exist regarding the effects of benzene on host resistance to infectious agents. This investigation examined the effects of benzene on murine resistance to an infectious agent, Listeria monocytogenes. Four concentrations of benzene were employed, 10, 30, 100, and 300 ppm. To determine recovery from the effects of benzene, two exposure regimens were employed: 5 days prior to infection (preexposure), or 5 days prior to and 7 days during infection (continuous exposure). Appropriate air controls were maintained. Splenic bacterial counts and immune responsive cell populations were determined from mice killed at Days 1, 4, and 7 of infection. Preexposure to benzene produced increased bacterial numbers at Day 4 of the infection only at the highest benzene concentration (300 ppm). In contrast, continuous exposure produced increased bacterial numbers at Day 4 of infection at all but the lowest benzene concentration (10 ppm). Bacteria counts were not increased in any benzene-treated group at Day 1 or Day 7 of infection. The increased bacterial numbers at Day 4 suggest an effect on cell-mediated immune responses. Both T and B lymphocytes were particularly sensitive to benzene exhibiting reductions at all concentrations greater than or equal to 30 ppm for both exposure regimens. Esterase-positive cells, however, were relatively resistant to benzenes effects. The results point to a benzene-induced delay in the immune response to L. monocytogenes.

Animals↗