Clearance and translocation of aluminum oxide (alumina) from the lungs.

Significant respiratory-tract exposure to insoluble aluminum compounds, such as alumina (aluminum oxide, Al(2)O(3)), can occur in occupational settings, yet little is known about the temporal pattern of pulmonary clearance of these materials from the lungs with repeated exposures, and potential subsequent translocation to other organs. This study evaluated the clearance pattern of alumina from the lungs of rats, and burdens in selected extrapulmonary organs (brain, bone, liver, spleen, kidney). Rats were instilled with alumina once weekly for 20 wk. Quantification of retention was performed by measuring aluminum burdens in the lungs and extrapulmonary organs during the exposure period, and then weekly for an additional 19 wk after the exposures ended. Lung burdens of aluminum were found to steadily increase during exposure. Clearance of the material following the end of the exposure regime was extremely slow; only approximately 9% of the amount in the lungs following the 20 weekly exposures was cleared by the end of the postexposure period. This study supports the concept of gradual accumulation and long-term retention of aluminum within the respiratory tract of individuals repeatedly exposed to alumina in occupational settings.

Gender- and age-specific cytotoxic susceptibility to benzene metabolites in vitro.

Benzene, a widely used compound, is a known carcinogen and hematopoietic toxicant. Several studies have shown gender and age differences in the responses to benzene-induced hematotoxicity. It is not known if these differences in response are due to age- or gender-associated metabolic differences or to age- or gender-associated differences in the susceptibilities of the target cells. In order to address this issue, mouse colony-forming units-erythroid (CFU-e, an erythroid precursor cell particularly susceptible to benzene toxicity) were cultured in the presence of either individual benzene metabolites or binary mixtures of these metabolites. CFU-e were obtained from unexposed age-matched adult male and female (both virgin and pregnant) Swiss Webster (SW) mice and from SW male and female 16-day fetuses. The metabolites used were phenol, hydroquinone, catechol, benzoquinone, and trans, trans-muconic acid. The concentrations of the individual metabolites used were 10, 20, and 40 microM. Binary mixtures of metabolites were prepared using the lowest concentrations of the individual metabolites that caused cytotoxicity. These concentrations were 10 microM for hydroquinone, catechol, and benzoquinone, and 40 microM for phenol and muconic acid. In general, the CFU-e from adult females (both virgin and pregnant) were more resistant to the toxic effects of the individual metabolites than CFU-e from other subjects. CFU-e from adult males were more susceptible to the cytotoxic effects of hydroquinone and benzoquinone than CFU-e from other subjects and CFU-e from both male and female fetuses were highly sensitive to the toxic effects of catechol. On the other hand, CFU-e from adult males were less susceptible to the cytotoxic effects of catechol than CFU-e from other subjects. Similar results were observed with binary mixtures of metabolites. CFU-e from adult males were more susceptible to the binary mixtures than CFU-e from virgin females and CFU-e from fetal males were more susceptible than CFU-e from fetal females. In addition, CFU-e from fetuses were more 'resistant than CFU-e from adults to the cytotoxic effects of those binary mixtures that did not contain catechol. In contrast, binary mixtures containing catechol were more toxic to fetal cells than to adult cells. These results suggest that differences in benzene hematotoxicity associated with gender and age may be due, at least in part, to intrinsic factors at the level of the target cell rather than solely to age- or gender-related differences in the metabolism of benzene.

An assessment of the tumorigenic properties of a Hudson County soil sample heavily contaminated with hexavalent chromium.

During much of this century, Hudson County, New Jersey, was a major center for the processing of chromium ore. Some of the residue from this processing was used in landfills and in construction materials throughout the county and, in some cases, in highly populated areas. Given that it is widely accepted that exposure to hexavalent chromium compounds poses a risk for the development of respiratory-tract cancer, concerns were raised that individuals who worked or resided in chromium-contaminated areas might be at increased risk for the development of respiratory cancer. To address these concerns, we evaluated a Hudson County soil sample-heavily contaminated with chromium ore residue (Cr(+6) concentration at 5 895 mg/kg)-with respect to its carcinogenic potential to the respiratory tract of Sprague-Dawley rats. Groups of animals were given repeated intratracheal exposures to one of four materials: (1) Hudson County chromium-contaminated soil (CCS), (2) CCS augmented with calcium chromate (CaCrO4), (3) CaCrO4 alone, or (4) control soil. Nominal total doses of Cr(+6) for each respective group were 324 microg/kg, 7,975 microg/kg, 8,700 microg/kg, and 0.02 microg/kg. Incidences of malignant tumors and nephritis were not elevated in any group. Four primary lung tumors appeared in animals that received CCS + CaCrO4, and one primary lung tumor appeared in the group treated with CaCrO4 alone. These incidences were not significant statistically, but the rare spontaneous occurrence of these tumors in Sprague-Dawley rats suggested that they were treatment related. No primary lung tumors appeared in the control or CCS-treated groups.

Butadiene inhalation accelerates arteriosclerotic plaque development in cockerels.

1,3-Butadiene (BD), a gas widely used in the rubber industry, is also present in automotive exhaust and in the vapor phase of environmental tobacco smoke (ETS; approximately 400 micrograms/cigarette). The threshold limit value (TLV) for BD which was 10 ppm, has now been reduced to 2 ppm. Extensive investigations of workers have identified very few statistically significant increases in BD-associated cancer mortality. However, two studies have reported increased BD-associated mortality from arteriosclerotic heart disease in black workers in the BD rubber industry. The cockerel is a sensitive animal model for studying effects of environmental agents on arteriosclerosis development. Previous studies showed that inhaled environmental levels of ETS significantly accelerate arteriosclerosis. Surprisingly, the carcinogen-rich tar fraction of ETS was ineffective. The elevated risk of death from arteriosclerotic heart disease in black BD workers and the high BD level in the vapor phase of ETS, raised the question of whether BD would accelerate arteriosclerosis in cockerels. Here, cockerels breathed either 20 ppm BD or filtered air (6 h/day, 80 days). Blinded measurements showed no differences between groups in plaque frequency or location. However, plaque sizes were significantly larger in BD-treated cockerels than in controls--results nearly identical to those reported earlier for ETS-exposed vs. air-exposed cockerels. This indicates that BD may contribute to the atherogenicity of ETS and provides experimental support for the recent reduction in the TLV for BD.

Cecal-colic adult intussusception as a cause of intestinal obstruction in Central Africa.

During a 5-year experience in Central Africa, the most common cause of 78 adult intestinal obstructions was primary adult cecal-colic intussusception (n = 43; 55%). The symptom complex of colicky abdominal pain and obstipation was present in 100% of the patients with intussusception. Operative repair in 90% of patients consisted of simple reduction of the intussusceptum. There were no known recurrences. The etiology of adult cecal-colic intussusception is unknown. Patients typically present with a 3- to 4-day history of abdominal pain, obstipation, and usually a palpable mass. Treatment is surgical reduction. Right colectomy is reserved for intestinal gangrene. We treated 43 cases during a 5-year period with only one death.

1,3 Butadiene, a vapor phase component of environmental tobacco smoke, accelerates arteriosclerotic plaque development.

BACKGROUND: Our recent results support predictions from epidemiology studies that thousands of excess heart disease-related deaths result yearly in the United States from involuntary exposure to environmental tobacco smoke (ETS). Limited exposures of cockerels to ETS significantly accelerate arteriosclerosis. Despite little direct in vivo support, tar fraction rather than vapor phase compounds are considered largely responsible for the plaque-promoting effects of cigarette smoke. Here, we evaluate the effects of two ETS components on plaque development: the vapor phase component, 1,3 butadiene, and the tar component, the tobacco-specific N-nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). At relatively high doses, injected NNK is carcinogenic in rodents. Epidemiology studies have identified increased mortality from arteriosclerotic heart disease among black men working in the butadiene rubber industry. Neither butadiene nor NNK has been tested experimentally for a possible role in plaque development. METHODS AND RESULTS: Cockerels inhaled butadiene (20 ppm; 16 weeks) or were injected biweekly with NNK (10 mg/kg, 16 weeks). Control cockerels were exposed to filtered air or were injected with the NNK solvent dimethylsulfoxide. Plaque incidence, prevalence, location, and size were determined double-blind. NNK had no significant effect on any of these measurements. In contrast, butadiene elicited a statistically significant increase in plaque size comparable to that seen after steady-state exposure to ETS from 5 cigarettes. CONCLUSION: (1) This study represents the first time that a single cigarette smoke component has been demonstrated to accelerate arteriosclerosis, at a dose that is environmentally relevant. (2) The plaque-promoting components of ETS may reside in the vapor phase. (3) The cockerel model should be valuable in understanding the mechanism underlying the reported increases in heart disease deaths among black workers in the butadiene rubber industry.

Reduced IL-6 levels among individuals in Hudson County, New Jersey, an area contaminated with chromium.

Hudson County, New Jersey, was a major center for the processing of chromium ore. After processing, some of the ore residue that contained low concentrations of chromium became distributed in population centers throughout the county. There now exists concern in the county about possible health effects from chromium exposure. Our previous research suggested that immune-function assays would make useful biomarkers for chromate exposure in humans. Blood samples were drawn from 46 individuals who lived and/or worked in Hudson County and from 47 controls. Only one of the immune-associated assays performed on these samples showed any statistically significant differences between the Hudson County and control groups. The mean level of IL-6 produced by pokeweed mitogen-stimulated mononuclear cells isolated from the Hudson County group was 64% of the control value--a highly significant decrease (p<.001). There was also a significant correlation between the proliferative responses of the mononuclear cells to pokeweed mitogen and the levels of IL-6 produced by these cells. No differences were detected in the IL-6 responses that resulted from age, gender, or smoking status. The reliability of the IL-6 assay was found to be 90%. To our knowledge, there have been no reports, until now, that describe reduced production of any cytokine in individuals who are exposed to chromate.

Influences of gender, development, pregnancy and ethanol consumption on the hematotoxicity of inhaled 10 ppm benzene.

The hematotoxic effects of benzene in both humans and animals are well documented. Current estimates concerning the risks associated with benzene exposure are usually based on adult, male cohort studies; however, there are indications that females may respond differently than males to benzene and that fetuses may respond differently than adults. Another factor to be considered in risk estimates is the impact of personal habits. In experimental animals, ethanol consumption is known to increase the hematotoxicity of benzene; therefore, alcohol consumption may also alter the potential risk of individuals exposed to benzene. To address some of the factors that may confound risk estimates for benzene exposure, a series of experiments were performed. Age-matched male as well as pregnant and virgin female Swiss Webster mice were exposed to 10 ppm benzene for 6 h a day over 10 consecutive days (days 6 through 15 of gestation for the pregnant females). Half of the animals also received 5% ethanol in the drinking water during this period. On day 11, bone marrow cells from the adults and liver cells from the fetuses were assayed for the numbers of erythroid colony-forming units (CFU-e). CFU-e assays were also performed on bone marrow cells isolated from 6-week postpartum dams exposed during gestation and from in utero-exposed 6-week old males and females. Gender differences were clearly observed in the responses to the various exposure protocols. Depressions in CFU-e numbers were only seen in male mice while elevations in CFU-e numbers were only seen in female mice. Male mice exposed as adults for 10 days to benzene (B), ethanol (E) or benzene+ethanol (B+E) exhibited depressed CFU-e levels as did male fetal mice exposed to B in utero. In addition, adult male mice which had been exposed in utero to either B or to E individually displayed depressed CFU-e levels. In contrast, none of the groups of female mice exhibited any depressions in CFU-e numbers after any of the exposures. Elevations in CFU-e numbers were observed among pregnant females exposed to E and among adult females exposed to B+E in utero. In summary, a majority (6/9) of the exposure protocols produced depressions in the CFU-e numbers of male mice, whereas a majority (7/9) of the exposure protocols produced no changes in the CFU-e numbers of female mice. Those changes that were observed in females consisted of elevations of CFU-e numbers. These results suggest that the male erythron is more susceptible than the female erythron to the hematotoxicants benzene and ethanol, regardless of whether exposures occur in utero or during adulthood.

Aspirin-like drugs can protect human T lymphocytes against benzoquinone cytotoxicity: evidence for a NAD(P)H:quinone reductase-dependent mechanism.

Benzene toxicity towards lymphocytes is thought to be mediated by metabolites of benzene including benzoquinone (BQ). NAD(P)H:quinone reductase (QR) is known to protect against BQ toxicity. The expression of the QR gene is regulated by the transcription factor AP-1. We had previously found that aspirin-like drugs (ALD) induce AP-1 in human T lymphocytes. It was therefore hypothesized that ALD would protect lymphocytes against BQ toxicity by inducing QR. Molt-4 cells (M4), a human T lymphocyte cell line, were incubated with different concentrations of two ALD, flurbiprofen and sodium diclofenac, and then exposed to BQ. Toxicity was measured by viability (trypan blue exclusion). Both drugs protected the cells against BQ cytotoxicity in a dose-dependent manner, e.g., sodium diclofenac at 15 microM reduced the fraction of BQ-treated dead cells by 70%. ALDs induced QR activity in the M4 cells in the same range of concentrations that protected the cells against BQ toxicity. The protective effect of ALD was significantly reduced by dicoumarol, a QR-specific inhibitor. Since human T cells and T cell lines do not metabolize arachidonic acid, our data suggest that ALD can protect human T lymphocytes against a metabolite of benzene by induction of QR activity.

Lead alters the immunogenicity of two neural proteins: a potential mechanism for the progression of lead-induced neurotoxicity.

Some heavy metals have been suspected of playing a role in the pathogenesis of nervous system diseases such as multiple sclerosis, amyotrophic lateral sclerosis, and Alzheimer's disease. In these disorders, autoantibodies against neural proteins are evident at some stage of the disease. Lead is known to affect both the immune and nervous systems. Work in our laboratory has shown that lead exposure leads to the production of autoantibodies against neural proteins, including myelin basic protein (MBP) and glial fibrillary acidic protein (GFAP). We hypothesize that lead aggravates neurological disease by enhancing the immunogenicity of nervous system proteins, including MBP and GFAP. To test this hypothesis, lead-altered protein was prepared by incubating MBP or GFAP with lead acetate for 24 hr. On days 0, 14, and 28, mice received inoculations with either saline, native protein, or lead-altered protein. Anti-MBP and anti-GFAP, isotypes IgM and IgG, were measured in sera by ELISA on day 38. Sera of mice treated with lead-altered MBP had statistically higher anti-MBP IgG titers than both control and native MBP-immunized mice. An analogous response was seen in mice immunized with lead-altered GFAP. Supernatants from lectin-stimulated splenocytes were also examined for antibody titers and for interleukin 2 (IL-2) and interleukin 6 (IL-6) levels. A significant increase in IL-6 production was seen in mice immunized with lead-altered MBP but not with lead-altered GFAP. No changes were observed in the IL-2 levels of mice immunized with either lead-altered protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of a pharmacokinetic model for chromium in the rat following subchronic exposure. I. The importance of incorporating long-term storage compartment.

A pharmacokinetic model of chromium depuration in the rat has been developed under subchronic exposure conditions. Rats were exposed to 100 ppm Cr(VI) in their drinking water for 6 weeks, followed by a 140-day period of depuration. Tissue concentrations of Cr at the end of the 6-week exposure period were greatest in the bone, spleen, and kidney, with lower concentrations present in the liver and blood. The overall kinetics of Cr depuration from the tissues were relatively slow, especially for the largest compartment which included bone. The results indicated that the half-life of Cr in bone exceeded 100 days. A three-compartment model was developed to fit the data. Liver, kidney, and spleen were grouped into a single compartment which was linked to a major storage compartment (i.e., bone, skin, hair, and muscle) via the blood. Using this model, the time to a 50% reduction of whole body Cr (i.e., loss of total Cr mass for the whole rat) was calculated to be about 80 days. The higher half-life for the storage compartment of 100 days is due to the relative weights of the compartments and the more rapid loss of Cr from the liver, kidney, and spleen compartment. The data suggest that Cr may be sequestered and release of Cr by the storage compartment over an extended period of time, thereby, may play an important role in maintaining elevated body burdens and tissue concentrations of Cr following long-term exposure to this toxic metal.

Inhalation of steady-state sidestream smoke from one cigarette promotes arteriosclerotic plaque development.

BACKGROUND: A number of epidemiologic studies have suggested that every year environmental tobacco smoke (second-hand smoke) is responsible for tens of thousands of deaths, mostly from heart disease, in the United States. Environmental tobacco smoke is composed mainly (80% to 85%) of aged and diluted sidestream smoke. The remainder is exhaled mainstream smoke. Among the thousands of compounds that have been identified in environmental tobacco smoke are a number of carcinogens, including polynuclear aromatic hydrocarbon carcinogens, such as benzo(a)pyrene. We have demonstrated previously that a number of carcinogens, including benzo(a)pyrene, promote plaque development after injection into cockerels. There have been almost no studies showing a direct stimulatory effect of environmental tobacco smoke on plaque development. Recently we demonstrated that cockerels exposed to sidestream smoke for approximately 0.4% of their projected lifespan exhibited accelerated development of arteriosclerotic plaques. In that study, cockerels in specially designed inhalation chambers were exposed to the steady-state sidestream smoke from 5 cigarettes for 6 h/d for 16 weeks. This level of exposure is high but environmentally plausible. Statistically significant increases in plaque size were demonstrated in the smoke-exposed cockerels. METHODS AND RESULTS: In the present study, exposure levels were decreased by a factor of 5. Thirty cockerels were exposed to the steady-state sidestream smoke from 1 cigarette for 6 hours per day for 16 weeks. The smoke was mixed with filtered air. Ten control cockerels were exposed to filtered air only. Levels of smoke surrogates, including carbon monoxide and total suspended particulates, were measured three times a day. Again, there was a statistically significant increase in plaque size in the smoke-exposed cockerels. To place these studies within a context of environmental relevance, levels of carbon monoxide were measured independently over 1 to 3 hours in four bars where there was heavy smoking. Measured carbon monoxide levels were as high or higher in the bars than they were in the exposure chambers during the 1-cigarette sidestream-smoke study. CONCLUSIONS: Experimental exposure to secondhand smoke at levels equal to or even below those routinely encountered by people in smoke-filled environments is sufficient to promote arteriosclerotic plaque development.

Erythroid progenitor cells that survive benzene exposure exhibit greater resistance to the toxic benzene metabolites benzoquinone and hydroquinone.

Benzene is a well known hematotoxicant which induces hematopoietic dyscrasias of varying intensities in different individuals and even in different strains of the same experimental animal species. Although there is ample evidence that diverse responses to benzene are related to differences in benzene metabolism, we have recently provided evidence implicating differences in host target cell susceptibility to these diverse responses to benzene. The present study extends our previous work and concerns strain-specific differences in marrow progenitor cells that survive benzene exposure. Two mouse strains (Swiss-Webster and C57B1/6J) which respond to benzene exposure with different intensities of bone marrow cytotoxicity were used. Bone marrow cells from benzene-exposed and untreated mice were cultured with one of five benzene metabolites: 1,4-benzoquinone (BQ), catechol (C), hydroquinone (HQ), muconic acid (MA) or phenol (P) and the abilities of these cells to produce erythroid (CFU-e) or granulocyte/macrophage colonies (GM-CFU-c) were assessed. In both strains, marrow cells isolated from benzene-exposed mice showed a higher percentage of plated CFU-e surviving culture with BQ, HQ or MA than marrow cells isolated from control mice. In contrast, both strains of benzene-exposed mice displayed decreased percentages of plated CFU-e surviving culture with catechol than cells isolated from control mice. Only one condition (the culturing of cells with HQ under GM-CFU-c forming conditions) showed any strain-specific difference in plating efficiency. In all, 20 possible combinations of benzene metabolites and cell types were examined (5 metabolites x 2 progenitor cell types x 2 strains).(ABSTRACT TRUNCATED AT 250 WORDS)

Inhalation of sidestream cigarette smoke accelerates development of arteriosclerotic plaques.

BACKGROUND: Environmental tobacco smoke has been blamed for approximately 40,000 excess deaths from heart disease annually in the United States. As yet, no pathophysiological process that could be responsible for these deaths has been identified. Environmental tobacco smoke is composed mainly of aged and diluted sidestream smoke but also contains 15% to 20% exhaled mainstream smoke. Carcinogens, including nitrosamines and polynuclear aromatic hydrocarbons, are present in mainstream smoke and sidestream smoke. Carcinogen levels in sidestream smoke, unlike those in mainstream smoke, are not reduced in filtered cigarettes. The US Environmental Protection Agency has designated environmental tobacco smoke as a human (class A) carcinogen. In cockerels, subtumorigenic doses of polynuclear aromatic hydrocarbons carcinogens accelerate aortic arteriosclerotic plaque development. METHODS AND RESULTS: To determine whether sidestream smoke inhalation affects arteriosclerotic plaque development, we exposed cockerels to sidestream smoke (n = 30) or to filtered air (n = 12) in inhalation chambers for 6 hours per day, 5 days a week from 6 to 22 weeks of age (0.4% of projected lifespan). Chamber levels of carbon monoxide, total suspended particulates, and nicotine were measured regularly during the exposures. The abdominal aorta from each cockerel was cut into 10 segments, and the plaque index (mean plaque cross-sectional area [mm2]/mean luminal circumference [mm] x 100) was calculated for each segment. There were no differences in plaque incidence or distribution between sidestream smoke-exposed and control cockerels; however, plaque indexes were significantly greater for sidestream smoke-exposed than control cockerels in all segments. CONCLUSIONS: Thus, relatively brief exposures to sidestream smoke early in life are sufficient to enhance arteriosclerotic plaque development.

The extent and persistence of binding to respiratory mucosal DNA by inhaled tritiated propylene oxide.

In order to investigate some of the mechanisms underlying the carcinogenicity of inhaled propylene oxide (PO), the deposition and persistence of inhaled tritiated PO in the DNA of the nasal cavities, tracheae and lungs of rats were investigated. The results of dose/response exposure protocols revealed clear gradients for binding throughout the respiratory mucosa; the highest levels of binding were in the nasal mucosa and the lowest were in the lungs. Gradients became steeper as exposure concentrations were lowered. The persistence studies revealed that bound tritium declined in nasal mucosal DNA with apparent bi-exponential kinetics while clearance from the tracheal and pulmonary DNA was much slower and occurred with apparent mono-exponential kinetics. Consequently, although the initial levels of binding of inhaled PO are lower in the trachea and lungs than in the nasal cavity, the slow clearance of PO from the DNA in these organs could increase the chances of a mutational event.

Effects of residual astigmatism in contact lens wear on visual discomfort in VDT use.

The purpose of this study was to evaluate the effects of the residual astigmatism of contact lens wearers on the visual comfort of these individuals when using a video display terminal (VDT). We hypothesized that small amounts of uncorrected residual astigmatism of the type that is normally left uncorrected produce visual discomfort in the use of these devices even though visual acuity is relatively unaffected. Twelve subjects (ages 18 to 36 years) with corrected visual acuities of at least 20/25 (in each eye at distance with their contact lens correction) participated. All subjects were soft contact lens wearers who reported comfortable, well-adapted lens wear for a minimum of 1 year prior to the study. All subjects had between 0.50 and 1.00 D of residual astigmatism in each eye (mean = 0.68D). Our double-masked cross-over experiment included two 25-minute periods during which the subject read from a VDT. In a trial frame over their contact lens correction, the subjects were randomly assigned to wear either a test lens pair or a control lens pair (+0.12 DS) during the first period and the alternative pair during the second period. The test lens pair corrected all residual astigmatism (the over refraction). The control lens pair was considered a placebo. A questionnaire was used to obtain ratings of visual discomfort. Our analysis of the data indicated greater reported visual comfort for the test lens pair (Wilcoxon signed-rank test, p less than 0.01). These results suggest careful consideration be given to the correction of residual astigmatism of contact lens wearers who are VDT users.

Evidence for strain-specific differences in benzene toxicity as a function of host target cell susceptibility.

It has long been recognized that benzene exposure produces disparate toxic responses among different species or even among different strains within the same species. There is ample evidence that species- or strain-dependent differences in metabolic activity correlate with the disparate responses to benzene. However, bone marrow cells (the putative targets of benzene toxicity) may also exhibit species- or strain-dependent differences in susceptibility to the toxic effects of benzene. To investigate this hypothesis, two sets of companion experiments were performed. First, two strains of mice, Swiss Webster (SW) and C57B1/6J (C57), were exposed to 300 ppm benzene via inhalation and the effects of the exposures were determined on bone marrow cellularity and the development of bone marrow CFU-e (Colony Forming Unit-erythroid, an early red cell progenitor). Second, bone marrow cells from the same strains were exposed in vitro to five known benzene metabolites (1,4 benzoquinone, catechol, hydroquinone, muconic acid, and phenol) individually and in binary combinations. Benzene exposure, in vivo, reduced bone marrow cellularity and the development of CFU-e in both strains; however, reductions in both these endpoints were more severe in the SW strain. When bone marrow cells from the two strains were exposed in vitro to the five benzene metabolites individually, benzoquinone, hydroquinone, and catechol reduced the numbers of CFU-e in both strains in dose-dependent responses, phenol weakly reduced the numbers of the C57 CFU-e only and in a non-dose-dependent manner, and muconic acid was without effect on cells from either strain.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.