Vitamin A metabolism in rats chronically treated with 3,3',4,4',5,5'-hexabromobiphenyl.

Chronic dietary administration of 3,3',4,4',5,5'-hexabromobiphenyl (HBB), 1 mg/kg diet, caused a decrease in retinol (20-fold) and retinyl esters (23-fold) in the livers of female rats, but resulted in a 6.4-fold increase in retinol and 7.4-fold increase in retinyl esters in the kidneys. Liver acyl-CoA:retinol acyltransferase and retinyl palmitate hydrolase activities were reduced while serum concentration of retinol was unaffected by HBB feeding. Metabolism of a physiological dose of [11-3H]retinyl acetate (10 micrograms), was examined in rats fed either vitamin A-adequate diet, or marginal amounts of vitamin A, or vitamin A-adequate diet containing HBB. A 13-fold greater amount of the administered vitamin A was found in kidneys of HBB-treated rats. In rats fed adequate or low amounts of vitamin A, kidney radioactivity was primarily in the retinol fraction, while in HBB-fed rats the radioactivity was associated mostly with retinyl esters. Fecal and urinary excretion of radioactivity was greatly increased in HBB-treated rats. Chronic HBB feeding results in a loss of ability of liver to store vitamin A, and severely alters the uptake and metabolism of vitamin A in the kidneys. We conclude that HBB causes major disturbances in the regulation of vitamin A metabolism.

drp, a novel protein expressed at high cell density but not during growth arrest.

Contact is a vital mechanism used by cells to interact with their environment. Contact with living and nonliving elements adjacent to a cell is the basis for many common biological events ranging from growth regulation to metastasis to embryonic pattern formation. We describe the cloning and characterization of a novel density-regulated protein (drp) whose expression is increased in cultured cells at high density compared with cells at low density. A drp cDNA was isolated from the human teratocarcinoma cell line PA-1. Northern analysis with a drp probe revealed transcripts of 2.8 and 3.2 kb. The drp RNA was expressed in a variety of tissues, with the highest amounts in skeletal and cardiac muscle. Using antipeptide antisera, increasing amounts of a 70-kDa protein were detected using several experimental approaches in several cells lines as cell density is increased. Conditioned medium from high-density cells was unable to induce expression of drp in cells growing at low density. Similarly, growth arrest by serum starvation or transforming growth factor-beta (TGF-beta) treatment failed to elicit drp expression. We conclude that drp is a novel protein whose expression is increased at high cell density but not growth arrest.

Aggregation of platelets from monocrotaline pyrrole-treated rats.

Aggregation responses of platelet-rich plasma (PRP) from monocrotaline pyrrole (MCTP)-treated rats were examined to help elucidate the role of platelets in MCTP-induced pulmonary hypertension. PRP from rats treated one or four days earlier with MCTP (5 mg/kg, i.v.) or vehicle exhibited the same slope and maximum aggregation to ADP (1 X 10(-5) M, 2 X 10(-6) M, 1 X 10(-6) M), 74 micrograms/ml dog collagen, or 500 micrograms/ml arachidonic acid. PRP collected 7 days after MCTP treatment had a 15% decrease in both slope and maximum aggregation to 1 X 10(-5) M ADP and a 25% decrease in response to 2 X 10(-6) M ADP relative to the control group. Fourteen days after MCTP treatment, the responses to all of the aggregating agents were decreased 18-71% from control values. These results indicate that MCTP treatment alters the responses of PRP to aggregating agents.

Tier-2 studies on monocrotaline immunotoxicity in C57BL/6 mice.

Monocrotaline (MCT) is a member of a class of naturally occurring phytotoxins known as pyrrolizidine alkaloids, and is a toxicological concern to both man and his livestock. The purpose of these studies was to evaluate the effect of a 14-day oral MCT (0-100 mg/kg per day) exposure on the functional integrity of various immunocyte effector systems in C57BL/6 mice, as well as to investigate potential mechanisms for its immunotoxicity. Decreases in lymphoid organ weights and cellularity, and resident peritoneal exudate cell (PEC) number were only observed after exposure to the highest dose of 100 mg/kg MCT. This dose also inhibited NK cell cytotoxicity, while the total number of NK lytic units per spleen was decreased (-53%) after exposure to 50 mg/kg MCT. Following i.p. injection of SRBC, the percentage of PEC macrophages containing engulfed SRBC was significantly increased in MCT-exposed mice, while the percentage of large vacuolated (activated) macrophages was decreased in a dose-dependent manner. Exposure to MCT significantly decreased the total number of Ig+ cells without altering the number of CD4+ and CD8+ cells. The antibody responses (PFC/10(6) spleen cells) to two T cell-independent antigens, TNP-LPS and DNP-Ficoll, were significantly decreased at all MCT doses, and the degree of suppression of both responses was identical at coincident doses. MCT exposure (25 mg/kg) significantly suppressed the blastogenic response to the T cell mitogen concanavalin A (-38%), and to the B cell mitogen lipopolysaccharide (-58%). These results indicate that exposure to MCT can alter the functional integrity of various immune effector responses in a dose-dependent manner, and suggest that the B cell may be a relatively more sensitive target of MCT immunotoxicity compared to T cells, macrophages and NK cells.

Role of metabolism in monocrotaline-induced immunotoxicity in C57BL/6 mice.

Monocrotaline (MCT) is a pyrrolizidine alkaloid which has been shown to induce immunotoxicity in mice. We hypothesized that metabolic activation of MCT by mixed-function oxygenases (MFO) to dehydromonocrotaline (MCTP) is a prerequisite for its immunotoxicity, as has been shown for other toxic effects of MCT. To test this hypothesis, we compared the in vitro immunotoxic potency of MCT and MCTP to suppress the in vitro antibody response to SRBC and the blastogenic response to B and T cell mitogens. In addition, the effects of in vivo modulation of MFO activities on the immunotoxicity of MCT was examined using phenobarbital (PB) to increase and chloramphenicol (CP) to decrease MCTP production. Results showed that in vitro exposure of splenic lymphocytes to MCT or MCTP produced significant suppression of the antibody and blastogenic responses. MCTP was 200-400-fold more potent than MCT. No metabolism of MCT by splenic cells was detectable, suggesting that unmetabolized MCT is capable of inducing immunotoxicity. In vivo studies showed that, while treatment of mice with PB or CP produced significantly increased and decreased MCTP production by liver microsomes, neither PB or CP treatment significantly altered the immunotoxic potency of MCT. Thus, while the MCTP metabolite is directly immunotoxic in vitro and much more potent than MCT, a role for the MCTP metabolite in MCT immunotoxicity in vivo could not be demonstrated.

Immunotoxicity of the pyrrolizidine alkaloid monocrotaline following subchronic administration to C57Bl/6 mice.

Monocrotaline (MCT) is a member of a class of compounds known as pyrrolizidine alkaloids (PAs). PAs are found in the leaves and seeds of a variety of plant species. The potential intoxication of livestock and man through the ingestion of contaminated grains and other foods makes PAs a significant toxicological concern. MCT exposure in rats results in lesions to hepatic and cardiopulmonary tissues as well as alterations in lymphoid organ cellularity. However, no previous studies have investigated MCT-induced functional alterations in the immune system. In the present study, MCT was administered by gavage for 14 days at 0, 10, 25, 50, 75, and 150 mg/kg to female C57Bl/6 mice. The antibody-mediated immune response to sheep red blood cells (SRBC) was assessed using the plaque-forming cell (PFC) assay and the hemolytic antibody isotope release assay (HAIR). Additionally, the cytotoxic T-lymphocyte (CTL) response to allogeneic P815 tumor cells was determined after MCT exposure. Although hepatic and pulmonary lesions are common sequelae to MCT exposure in rats, the C57Bl/6 mouse appeared to be more resistant to these effects on the basis of histopathological examination. Furthermore, the overt toxicity of MCT was minimal with respect to organ weight changes in liver, kidney, and lung. In contrast, a dose-dependent suppression in the antibody response to SRBC was observed with a minimum significant dose of 25 mg/kg. At this dose the number of anti-SRBC PFC per 10(6) spleen cells and the amount of anti-SRBC antibody measured in the HAIR assay were 57 and 59% of control, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Review of subchronic/chronic toxicity of antimony potassium tartrate.

Subchronic/chronic toxicity studies on antimony potassium tartrate (APT) have been reviewed. One of the older studies (H. A. Schroeder et al., 1970, J. Nutr. 100 (1), 59-68), on which are based the EPA reference dose value and a number of state, national, and international drinking water criteria for antimony, has severe inadequacies in study conduct making it uninterpretable and inappropriate for characterization of APT toxicity. In particular, the manner in which control data were generated and utilized in this study is considered invalid. More recent drinking water studies conducted by the NTP (1992, "NTP Technical Report on Toxicity Studies of Antimony Potassium Tartrate in F344/N Rats and B6C3F(1) Mice (Drinking Water and Intraperitoneal Injection Studies)," NTP Toxicity Report Series, No. 11) and Poon et al. (1998, Food Chem. Toxicol. 36, 20-35) showed antimony to be of low toxicity. The NOAEL in the 14-day NTP study was 2500 ppm by the oral route in both rats and mice, while Poon et al. (1998) suggested a NOAEL of 0.5 ppm in their 90-day study. However, upon close examination, it was determined that this value was based on subtle histological changes in the thyroid gland that were physiological, not toxicological, in nature. This conclusion is supported further by an absence of these changes in a well-conducted 13-week intraperitoneal exposure study in rats that utilized APT at much higher doses (NTP, 1992). Thus, the NOAEL by Poon et al. (1998) should more appropriately be 50 ppm. When regulatory criteria for antimony are established and/or reviewed, the findings in the NTP study and this critical reevaluation of the Poon et al. (1998) study should be considered when establishing a NOAEL for subchronic exposure to antimony in the future.

Polychlorinated biphenyl-induced immune suppression: castration, but not adrenalectomy or RU 38486 treatment, partially restores the suppressed cytotoxic T lymphocyte response to alloantigen.

The cytotoxic T lymphocyte (CTL) response to allogeneic P815 tumor in C57bl/6 mice is dose-dependently suppressed after treatment with 3,3',4,4',5,5'-hexachlorobiphenyl (HxCB). Elevation of plasma corticosterone (CS) is also observed coincident with CTL suppression. Because immune suppression is inducible by glucocorticoid administration, the role of elevated CS was investigated as an indirect mechanism of HxCB-induced immunotoxicity. In multiple experiments, HxCB treatment (10 mg/kg b.w.) consistently reduced CTL activity by 70 to 85% in male mice. Adrenalectomy failed to alter the suppression of CTL activity by HxCB. However, the mortality rate was high (> or = 70%) in these experiments and plasma CS elevation persisted in HxCB-treated adrenalectomy survivors. Therefore, the use of adrenalectomized mice was inadequate to determine whether CS elevation leads to CTL suppression after HxCB treatment. Daily administration of the glucocorticoid receptor antagonist 17-beta-hydroxy-11-beta-(4-dimethylaminophenyl)-17-alpha-(propanyl )-estra- 4,9-dien-3-one (RU 38486) (150 mg/kg b.w., p.o.) also failed to alter the suppression of CTL activity in HxCB-treated mice; however, spleen cellularity was significantly increased, suggesting functional GCR antagonism. Male mice were more sensitive to HxCB-induced CTL suppression than female mice, and HxCB-induced plasma CS elevation was greater in male mice. Castration failed to reduce the elevation of plasma CS in HxCB-treated male mice. However, castration partially alleviated CTL suppression in HxCB-treated male mice.(ABSTRACT TRUNCATED AT 250 WORDS)

English plantain and psyllium: lack of cross-allergenicity by crossed immunoelectrophoresis.

BACKGROUND: English plantain (Plantago lanceolata) weed pollen and psyllium (Plantago ovata) husk dust are inhalant allergens. Because of the phylogenetic relationship between these plant species, cross-allergenicity has been a concern. OBJECTIVE: The purpose of this study was to investigate the possible cross-allergenicity of plantain and psyllium. METHODS: Homologous and heterologous crossed immunoelectrophoresis (CIE) were performed using a commercial English plantain pollen extract and an extract of psyllium seed embryo. Crossed radioimmunoelectrophoresis (CRIE) was performed using sera from subjects who were RAST positive only to plantain (group A), RAST positive only to psyllium (group B), RAST positive to both plantain and psyllium (group C), or RAST negative to both (group D). RESULTS: All of the group A plantain subjects showed IgE binding to at least one of the six plantain allergens in homologous plantain CRIEs while only one of the sera from the group B subjects reacted very weakly to these plantain allergens. In homologous psyllium CRIE, all group B subjects showed pronounced IgE binding to 2 to 7 of the seven psyllium allergens. Several of the plantain subjects demonstrated only very weak binding to psyllium allergens. Heterologous CRIEs demonstrated little relevant IgE binding. CONCLUSIONS: These results indicate that there is little cross-allergenicity between psyllium husk and English plantain pollen.

Influence of the Ah locus on the humoral immunotoxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin: evidence for Ah-receptor-dependent and Ah-receptor-independent mechanisms of immunosuppression.

There are conflicting reports in the literature regarding the role of the Ah locus in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) immunotoxicity. The present studies have utilized two congenic strains of C57Bl/6 mice that differ only at this locus to assess its influence on TCDD-induced suppression of antibody responses. Mice were given a single oral dose of TCDD 2 days prior to challenge with sheep red blood cells (SRBC) or trinitrophenyl-lipopolysaccharide (TNP-LPS). The subsequent dose-dependent effects of TCDD on the amount of antibody produced by splenic plasma cells were measured using the hemolytic antibody isotope release assay. In addition, the relative importance of the Ah genotype of lymphoid versus nonlymphoid tissue was examined in adoptive transfer experiments. Aryl hydrocarbon hydroxylase (AHH) activity was significantly induced in Ahbb mice by a dose of 0.5 micrograms/kg TCDD and maximally induced by a dose of 2 micrograms/kg. Ahdd mice required 10-fold higher doses of TCDD to induce comparable levels of AHH. The degree of thymic involution and liver hypertrophy induced by TCDD was also influenced by the Ah genotype of the animals. Both Ahbb and Ahdd mice exhibited dose-dependent suppression of the anti-TNP response following TCDD exposure. The ID50 was 7.0 micrograms/kg in Ahbb mice and 30.8 micrograms/kg in Ahdd mice. Suppression of the antibody response to SRBC was also dependent on the Ah locus. The ID50 in Ahbb mice was 0.6 micrograms/kg TCDD. However, an apparent biphasic dose response for suppression of the anti-SRBC response in Ahdd mice suggested the involvement of an Ah-independent component of suppression as well. In adoptive transfer studies, lymphocytes were identified as an Ah-dependent component of the response. The Ah-independent component of the response was not identified, and could be either lymphoid or nonlymphoid in nature. The possibility that T helper cells represent the Ah-independent component is discussed.