Interactions of Paraquat and Triadimefon: Behavioral and Neurochemical Effects

Triadimefon (TDF), a triazole fungicide, and paraquat (PQ), a non-selective herbicide/dessicant, are both known to adversely impact brain dopaminergic function and are used in overlapping geographical areas of the US. Since "real world" situations indicate humans are exposed to a diverse mixture of chemicals, this study hypothesized that combined exposures to PQ+TDF could produce interactive effects by simultaneously attacking multiple target sites of dopamine systems. Thus, 10 mg/kg PQ (PQ10) and 25 or 50 mg/kg TDF (TDF25 and 50, respectively) were administered i.p. to male C57BL/6 mice, 2x per week for 12 weeks, either alone or in combination. Acutely, TDF50 increased horizontal and vertical activity with increased vertical activity still occurring 24h later, indicative of sustained behavioral sensitization. Acutely, PQ decreased horizontal but not vertical activity with a lack of residual effects at 24h. PQ prevented the increased levels of activity associated with TDF50. These interactions differed for horizontal and vertical activity, indicating their differential neurochemical mediation, and suggesting that they did not arise from simple additivity of PQ and TDF effects. Nor could the interactive effects be readily ascribed to corresponding neurochemical interactions, since all treatments generally increased levels of DA and metabolites acutely in striatum and were associated with general reductions in levels of DA and metabolites and turnover in striatum and frontal cortex 7 days after the final treatment. Thus, TDF and PQ both separately and through interactions may serve as environmental risk factors through different mechanisms for dopaminergically-mediated behavioral dysfunctions.

Antitumor activity and toxicity of novel nitroheterocyclic phosphoramidates

A series of novel nitroheterocyclic phosphoramidates has been evaluated for antitumor activity in murine and xenograft tumor models and for toxicity in mice. Significant increases in lifespan and long-term survivors were noted in L1210 leukemia and B16 melanoma models, and both complete and partial tumor regressions were observed in the MX-1 breast cancer xenograft model. All compounds exhibited some degree of toxicity to granulocyte/macrophage progenitors in the bone marrow of mice. Two drugs were selected for further toxicologic, histopathologic, and pharmacokinetic evaluations. Toxicity of potential clinical significance was observed only in the bone marrow at the highest drug dose; otherwise no significant abnormalities in blood chemistries or organ histopathology were noted. The bone marrow lesions consisted of reduced numbers of progenitor cells in the myeloid and erythroid series; platelets were not affected. The compounds were eliminated rapidly by first-order kinetics, with half-lives in the 4-12 min range. The best of these compounds exhibits excellent antitumor activity and minimal toxicity at therapeutically effective doses in mice.

The nigrostriatal dopaminergic system as a preferential target of repeated exposures to combined paraquat and maneb: implications for Parkinson's disease

Experimental evidence supporting 1,1'-dimethyl-4,4'-bipyridinium [paraquat (PQ)] as a risk factor for Parkinson's disease (PD) is equivocal. Other agricultural chemicals, including dithiocarbamate fungicides such as manganese ethylenebisdithiocarbamate [maneb (MB)], are widely used in the same geographical regions as paraquat and also impact dopamine systems, suggesting that mixtures may be more relevant etiological models. This study therefore proposed that combined PQ and MB exposures would produce greater effects on dopamine (DA) systems than would either compound administered alone. Male C57BL/6 mice were treated twice a week for 6 weeks with intraperitoneal saline, 10 mg/kg paraquat, 30 mg/kg maneb, or their combination (PQ + MB). MB, but not PQ, reduced motor activity immediately after treatment, and this effect was potentiated by combined PQ + MB treatment. As treatments progressed, only the combined PQ + MB group evidenced a failure of motor activity levels to recover within 24 hr. Striatal DA and dihydroxyphenylacetic acid increased 1-3 d and decreased 7 d after injections. Only PQ + MB reduced tyrosine hydroxylase (TH) and DA transporter immunoreactivity and did so in dorsal striatum but not nucleus accumbens. Correspondingly, striatal TH protein levels were decreased only by combined PQ + MB 5 d after injection. Reactive gliosis occurred only in response to combined PQ + MB in dorsal-medial but not ventral striatum. TH immunoreactivity and cell counts were reduced only by PQ + MB and in the substantia nigra but not ventral tegmental area. These synergistic effects of combined PQ + MB, preferentially expressed in the nigrostriatal DA system, suggest that such mixtures could play a role in the etiology of PD.

Bcl-2 family gene expression during severe hyperoxia induced lung injury

Exposure of the lung to severe hyperoxia induces terminal transferase dUTP end-labeling (TUNEL) indicative of DNA damage or apoptosis and increases expression of the tumor suppressor p53 and of members of the Bcl-2 gene family. Because cell survival and apoptosis are regulated, in part, by the relative abundance of proteins of the Bcl-2 family, we hypothesized that lung cells dying during exposure would show increased expression of pro-apoptotic members, such as Bax, whereas surviving cells would have increased expression of anti-apoptotic members, such as Bcl-X(L). The hypothesis is tested in the current study by determining which Bcl-2 genes are regulated by hyperoxia, with specific focus on correlating expression of Bax and Bcl-X(L) with morphologic evidence of apoptosis or necrosis. Adult mice exposed to greater than 95% oxygen concentrations for 48 to 88 hours had increased whole-lung mRNA levels of Bax and Bcl-X(L), no change in Bak, Bad, or Bcl-2, and decreased levels of Bcl-w and Bfl-1. In situ hybridization revealed that hyperoxia induced Bax and Bcl-X(L) mRNA in uniform and overlapping patterns of expression throughout terminal bronchioles and parenchyma, coinciding with TUNEL staining. Electron microscopy and DNA electrophoresis, however, suggested relatively little classical apoptosis. Unexpectedly, Western analysis demonstrated increased Bcl-X(L), but not Bax, protein in response to hyperoxia. Bax and Bfl-1 were not altered by hyperoxia in p53 null mice; however, oxygen toxicity was not lessened by p53 deficiency. These findings suggest that oxygen-induced lung injury does not depend on the relative expression of these Bcl-2 members.

Potentiated and preferential effects of combined paraquat and maneb on nigrostriatal dopamine systems: environmental risk factors for Parkinson's disease?

The absence of any compelling basis for a heritable basis of idiopathic Parkinson's disease (PD) has focused attention on environmental exposures as causative agents. While the herbicide paraquat has repeatedly been implicated, its impact on dopamine systems following systemic exposures is equivocal. The restricted focus on paraquat also ignores the extensive geographical overlap of its use with other agrichemicals known to adversely impact dopamine systems, including ethylenebisdithiocarbamate fungicides such as maneb. The present study sought to determine whether combined exposures to paraquat and maneb would produce additive effects and support a multiple-hit environmental contribution to PD. C57BL/6 mice were exposed to either paraquat (5-10 mg/kg) or maneb (15-30 mg/kg) i.p. alone or in combination once a week for 4 weeks. Sustained decreases in motor activity immediately following injections were consistently observed only with combined exposures, with activity levels returning to control values 24 h later. Concurrently, levels of dopamine and metabolites and dopamine turnover were increased immediately post-injection only by combined exposures, and returned to control levels or below within 48 h. Reductions in tyrosine hydroxylase immunoreactivity, measured 3 days after the last injection, resulted only from combined exposure and were detected in dorsal striatum, but not in the nucleus accumbens. The fact that combined exposures resulted in potentiated effects that appear to target nigrostriatal dopamine systems suggests that these combinations may be important environmental risk factors for Parkinsonism. These findings also raise questions about the adequacy of current risk assessment guidelines for these chemicals which are based on effect levels derived from exposures to single agents.

Immunohistochemical localization of the acylases that catalyze the deacetylation of N-acetyl-L-cysteine and haloalkene-derived mercapturates

Acylases catalyze the hydrolysis of a range of S-substituted N-acetyl-L-cysteines. The hydrolysis of N-acetyl-L-cysteine is catalyzed by cytosolic acylase I, and activity is present in human endothelial cells and rat lung, intestinal, and liver homogenates. Many haloalkenes are metabolized to mercapturates, which also undergo acylase-catalyzed hydrolysis. The acylases that catalyze the deacetylation of N-acetyl-L-cysteine and several haloalkene-derived mercapturates have been recently identified: acylase I catalyzes the deacetylation of N-acetyl-L-cysteine and some haloalkene-derived mercapturates whereas an acylase purified from rat kidney cytosol catalyzes the deacetylation of a distinct set of substrates, including several haloalkene-derived mercapturates. The objective of these studies was to examine the tissue and subcellular localization of acylase I and purified rat kidney acylase. Immunoblotting showed the presence of immunoreactive acylase I and purified rat kidney acylase in rat kidney, liver, lung, and brain. Both acylases were identified by immunohistochemistry in several rat organs, including kidney, liver, lung, brain, stomach, intestines, adrenals, pancreas, and testis, indicating that acylase activity is widespread in rat tissues.

Effect of 40-kHz ultrasound on acute thrombotic ischemia in a rabbit femoral artery thrombosis model: enhancement of thrombolysis and improvement in capillary muscle perfusion

BACKGROUND

We have shown previously that 40-kHz ultrasound (US) at low intensity accelerates fibrinolysis in vitro with little heating and good tissue penetration. These studies have now been extended to examine the effects of 40-kHz US on thrombolysis and tissue perfusion in a rabbit model.

METHODS AND RESULTS

Treatment was administered with either US alone at 0.75 W/cm(2), streptokinase alone, or the combination of US and streptokinase. US or streptokinase resulted in minimal thrombolysis, but reperfusion was nearly complete with the combination after 120 minutes. US also reversed the ischemia in nonperfused muscle in the absence of arterial flow. Tissue perfusion decreased after thrombosis from 13. 7+/-0.2 to 6.6+/-0.8 U and then declined further to 4.5+/-0.4 U after 240 minutes. US improved perfusion to 10.6+/-0.5 and 12.1+/-0. 5 U after 30 and 60 minutes, respectively. This effect was reversible and declined to pretreatment values after US was discontinued. Similarly, tissue pH declined from normal to 7.05+/-0. 02 after thrombosis, but US improved pH to 7.34+/-0.03 after 60 minutes. US-induced improvement in tissue perfusion and pH also occurred after femoral artery ligation, indicating that thrombolysis did not cause these effects.

CONCLUSIONS

40-kHz US at low intensity markedly accelerates fibrinolysis and also improves tissue perfusion and reverses acidosis, effects that would be beneficial in treatment of acute thrombosis.

Evaluation of the safety of fenbendazole in cats

OBJECTIVE

To evaluate the safety of fenbendazole in domestic cats.

ANIMALS

28 six- to seven-month old domestic short-hair cats.

PROCEDURE

Cats were randomly assigned to 1 of 3 treatment groups or a control group (n = 7/group). Cats in the treatment groups were given fenbendazole at a dosage of 50, 150, or 250 mg/kg, PO, every 24 hours for 9 days; control cats were given a placebo. A fecal examination, coagulation tests, serum biochemical analyses, CBC, and urinalyses were performed before and 5, 9, and 21 days after initiation of treatment; cats were closely monitored for adverse reactions. After the last dose of fenbendazole was given, 4 control cats and 4 cats given fenbendazole at the highest dosage were euthanatized, and necropsies were performed.

RESULTS

None of the cats developed any adverse reactions. For cats in the control and all treated groups, laboratory test results were within reference limits, and there were no significant differences in results of laboratory tests among groups. No gross or histologic lesions were identified in the control or treated cats that were euthanatized.

CONCLUSIONS AND CLINICAL RELEVANCE

Fenbendazole administered to healthy cats at a dosage 5 times the dosage and 3 times the duration approved for use in dogs and wild felids did not cause any acute or subacute adverse reactions or pathologic changes. Results suggest that cats may be safely treated with fenbendazole.

Lack of cyclooxygenase-2 inhibits growth of teratocarcinomas in mice

Two isoforms of cyclooxygenase (COX-1 or COX-2) have been identified in the prostanoid biosynthetic pathway. The constitutive form, COX-1, is thought to maintain cellular homeostasis and the inducible form, COX-2, is recognized as a primary response gene thought to be involved in modulating cell proliferation and differentiation. To further characterize the role of the cyclooxygenases in cell proliferation, differentiation, and tumorigenicity we developed embryonic stem (ES) cell lines which contain homozygous disruptions in either the COX-1 or the COX-2 gene. These lines were then examined in terms of their viability, proliferation, and in vitro differentiation potential. Our results demonstrate that the wild-type ES cells do not express either COX-1 or COX-2 until the cells undergo differentiation. And the lack of either cyclooxygenase has no apparent effect on ES cell proliferation in vitro. However, the absence of a functional COX-2 gene leads to a dramatic reduction in the formation and growth of teratocarcinomas that appear when ES cells are injected into syngeneic mice. Histological microscopy shows that the few very small tumors that were generated from ES cells lacking COX-2 appear more differentiated than tumors emerging from COX-1 -/- or wild-type cells by exhibiting greater keratinization in the areas of squamous epithelium and the ossification of bone-forming cartilage. We conclude that the presence of a functional COX-2 enzyme is necessary for the efficient growth of these teratocarcinomas in animals.

A chimeric aryl hydrocarbon receptor knockout mouse model indicates that aryl hydrocarbon receptor activation in hematopoietic cells contributes to the hepatic lesions induced by 2,3,7, 8-tetrachlorodibenzo-p-dioxin

Pathologic changes associated with 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) exposure have been reported in the livers of a wide range of species. While these changes have been extensively described, the mechanisms of toxic interaction(s) that produce these lesions remain unclear. Using an aryl hydrocarbon receptor (Ahr) knockout male mouse chimeric model, we investigated whether the presence of this receptor in hematopoietic and/or parenchymal cells affects TCDD-induced hepatotoxicity. Bone marrow chimeras were produced by hematopoietic reconstitution of irradiated mice. Specifically, chimeras were generated with aryl hydrocarbon receptor (AHR) positive hematopoietic and parenchymal cells (Ahr+/+ animal bone marrow cells into irradiated Ahr+/+ animals), AHR positive hematopoietic and negative parenchymal cells (Ahr+/+ into Ahr-/-), AHR negative hematopoietic and positive parenchymal cells (Ahr-/- into Ahr+/+), and AHR negative hematopoietic and parenchymal cells (Ahr-/- into Ahr-/-). Male wild-type (Ahr+/+) and knockout (Ahr-/-) animals were used as nonchimeric controls. Following TCDD treatment (30 microg/kg body wt), liver sections from mice in each control and chimeric group were histologically evaluated for necrotic and inflammatory changes. TCDD treatment produced moderate inflammation in Ahr+/+ controls and Ahr+/+ into Ahr+/+ chimeras. This response was mild in TCDD-treated Ahr-/-, Ahr-/- into Ahr-/-, Ahr+/+ into Ahr-/-, and Ahr-/- into Ahr+/+ animals and was not different from the corresponding vehicle-treated groups. Moderate necrosis was observed in all TCDD-treated controls or chimeras with AHR-positive parenchyma. No or mild necrosis was observed in TCDD- and vehicle-treated animals containing AHR-negative parenchyma. These data indicate that the presence of AHR in hepatic parenchyma alone is sufficient for TCDD induction of hepatic necrosis, and its presence in hematopoietic cells is necessary for the inflammatory response to TCDD-induced hepatic lesions.

Prenatal and lactational exposure to methylmercury affects select parameters of mouse cerebellar development

Animal studies of the neuropathological effects of prenatal methylmercury (MeHg) seldom use regimens that represent environmental exposures. While acute administration of high doses of MeHg to developing rodents can model some of the outcomes MeHg produces in the human cerebellum, their long-term relevance to cerebellar development is unknown. The present study was undertaken to determine the effect of chronic dietary exposure to MeHg. Pregnant mice were exposed throughout gestation to 0.0 or 4.0 ppm methylmercury in their drinking water. Postpartum exposure of pups and lactating dams continued to postnatal day (PND) 30. On PND7, 14, 21, and 30, several morphometric indices of cerebellar cortex development, as well as blood and brain levels of total Hg, were measured in pairs of male and female littermates. No signs of overt toxicity were observed in the dams or offspring. Blood and brain levels of total Hg were highest in the exposed PND7 offspring and fell throughout the sampling period despite continued exposure. In a region of molecular layer in the anterodorsal lobe, MeHg exposure reduced the density of migrating cells in PND7 offspring. Molecular layer widths were reduced in PND30 offspring. In a region of the inferior lobe of PND7 offspring, MeHg exposure reduced external granular layer widths and decreased the density of migrating cells in the molecular layer. However, MeHg did not affect cerebellar cortex development in the central lobe, suggesting a regional sensitivity to chronic, low-level MeHg exposure during development.

Fate and toxicity of 2-(fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (compound A)-derived mercapturates in male, Fischer 344 rats

BACKGROUND

2-(Fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (compound A) is formed in the anesthesia circuit by the degradation of sevoflurane. Compound A is nephrotoxic in rats and undergoes metabolism by the mercapturic acid pathway in rats and humans to yield the mercapturates S-[2-(fluoromethoxy)-1,1,3,3,3-pentafluoropropyl]-N-acetyl-L -cysteine (compound 3) and S-[2(fluoromethoxy)-1,3,3,3-tetrafluoro-1-propenyl]-N-acetyl-L-cys teine (compound 5). These experiments were designed to examine the fate and nephrotoxicity of compound A-derived mercapturates in rats.

METHODS

The deacetylation of compounds 3 and 5 by human and rat kidney cytosol and with purified acylases I and III was measured, and their nephrotoxicity was studied in male Fischer 344 rats. The metabolism of the deuterated analogs of compounds 3 and 5, [acetyl-2H3]S-[2-(fluoromethoxy)-1,1,3,3,3-pentafluoropropyl ]-N-acetyl-L-cysteine (compound 3-d3) and [acetyl-2H3]S-[2-(fluoromethoxy)-1,3,3,3-tetrafluoro-1-propenyl]-N -acetyl-L-cysteine (compound 5-d3), respectively, was measured.

RESULTS

Compound 5, but not compound 3, was hydrolyzed by human and rat kidney cytosols and by acylases I and III. 19F nuclear magnetic resonance spectroscopic analysis showed no urinary metabolites of compound 3, but unchanged compound 5 and its metabolites 2-(fluoromethoxy)-3,3,3-trifluoropropanoic acid and 2-[1-(fluoromethoxy)-2,2,2-trifluoroethyl]-4,5-dihydro-1,3-thiazol e-4-carboxylic acid were detected in urine. Compound 5 (250 microM/kg) produced clinical chemical and morphologic evidence of renal injury in two of three animals studied.

CONCLUSIONS

Compounds 3 and 5 underwent little metabolism. Compound 5, but not compound 3, was mildly nephrotoxic. These results indicate that compound A-derived mercapturate formation constitutes a detoxication pathway for compound A.

Aryl hydrocarbon receptor activation in genital tubercle, palate, and other embryonic tissues in 2,3,7, 8-tetrachlorodibenzo-p-dioxin-responsive lacZ mice

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates the toxicity of 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) and related halogenated aromatic hydrocarbons. Although the normal function and endogenous ligand for this receptor are not known, it is thought to have a role in growth regulation processes. The AhR has been found in both adult and certain developing tissues, and AhR agonists like the environmental contaminant TCDD cause a number of developmental anomalies. We sought to determine whether the AhR is directly activated to a transcriptionally functional form in tissues known to be adversely affected by AhR agonist exposure. To this end, a transgenic mouse model was developed that could be used to indicate the temporal and spatial context of transcriptionally active AhR following agonist exposure in vivo. A synthetic promoter containing two dioxin-responsive elements (DREs) and a minimal TATA box was strongly induced by TCDD in transfected cells when linked to the lacZ or luciferase reporter gene. Transgenic mice harboring the lacZ construct had TCDD-inducible beta-galactosidase activity in tissues following adult and in utero exposure. Embryonic lacZ expression was induced in hard and soft palates, genital tubercle, certain facial regions, shoulder, as well as other tissues by in utero exposure to 30 microg TCDD/kg at Gestational Day 13. The most intense reporter response was observed in the genital tubercle. Histopathology of the palate and tubercle demonstrated the reporter gene activity to be both cell- and region-specific. This is the first publication to correlate reported TCDD-elicited toxicity (e.g., cleft palate in mice) with TCDD-dependent AhR activation. These data indicate the ability of TCDD to initiate a signal transduction process leading to a transcriptionally active AhR in these tissues, thereby identifying potential targets of dioxin-induced toxicity during development. Weak activation of the reporter gene was consistently observed only in the genital tubercle in the absence of exogenous inducer. This indicates minimal or no endogenous AhR activators at the developmental stage examined. This mouse model will prove useful for both the examination of the endogenous role of the AhR in proliferation or differentiation and of the developmental targets of dioxin-like compounds.

NF-kappa B-dependent inhibition of apoptosis is essential for host cellsurvival during Rickettsia rickettsii infection

The possibility that bacteria may have evolved strategies to overcome host cell apoptosis was explored by using Rickettsia rickettsii, an obligate intracellular Gram-negative bacteria that is the etiologic agent of Rocky Mountain spotted fever. The vascular endothelial cell, the primary target cell during in vivo infection, exhibits no evidence of apoptosis during natural infection and is maintained for a sufficient time to allow replication and cell-to-cell spread prior to eventual death due to necrotic damage. Prior work in our laboratory demonstrated that R. rickettsii infection activates the transcription factor NF-kappa B and alters expression of several genes under its control. However, when R. rickettsii-induced activation of NF-kappa B was inhibited, apoptosis of infected but not uninfected endothelial cells rapidly ensued. In addition, human embryonic fibroblasts stably transfected with a superrepressor mutant inhibitory subunit Ikappa B that rendered NF-kappa B inactivatable also underwent apoptosis when infected, whereas infected wild-type human embryonic fibroblasts survived. R. rickettsii, therefore, appeared to inhibit host cell apoptosis via a mechanism dependent on NF-kappa B activation. Apoptotic nuclear changes correlated with presence of intracellular organisms and thus this previously unrecognized proapoptotic signal, masked by concomitant NF-kappa B activation, likely required intracellular infection. Our studies demonstrate that a bacterial organism can exert an antiapoptotic effect, thus modulating the host cell's apoptotic response to its own advantage by potentially allowing the host cell to remain as a site of infection.

Nephrotoxicity of the glutathione and cysteine S-conjugates of the sevoflurane degradation product 2-(fluoromethoxy)-1,1,3,3, 3-pentafluoro-1-propene (Compound A) in male Fischer 344 rats

2-(Fluoromethoxy)-1,1,3,3,3-pentafluoro-1-propene (Compound A) is a halogenated alkene that is nephrotoxic in rats when administered by inhalation or intraperitoneally. Compound A undergoes glutathione-dependent metabolism: Compound A-derived glutathione S-conjugates and mercapturates are excreted in the bile and urine, respectively, of rats given Compound A. The present experiments were designed to study the nephrotoxicity of the Compound A-derived glutathione and cysteine S-conjugates, S-[2-(fluoromethoxy)-1,1,3,3, 3-pentafluoropropyl]glutathione , S-[2-(fluoromethoxy)-1,3,3, 3-tetrafluoro-1-propenyl]glutathione , S-[2-(fluoromethoxy)-1,1,3,3, 3-pentafluoropropyl]-L-cysteine and S-[2-(fluoromethoxy)-1,3,3, 3-tetrafluoro-1-propenyl]-L-cysteine . Conjugates , and given intraperitoneally produced dose-dependent nephrotoxicity that was characterized by diuresis, increased excretion of glucose and protein, elevated blood urea nitrogen concentrations and severe morphological changes in the kidneys, particularly in the proximal tubules. Glutathione S-conjugate , at a dose of 500 micromol/kg, was hepatotoxic. Cysteine S-conjugate was not nephrotoxic, apparently because of its facile cyclization to the thiazoline 2-[1-(fluoromethoxy)-2,2,2-trifluoroethyl]-4,5-dihydro-1, 3-thiazole-4-carboxylic acid, which is not a beta-lyase substrate. Also, the alpha-methyl analog of cysteine S-conjugate S-[2-(fluoromethoxy)-1,1,3,3, 3-pentafluoropropyl]-DL-alpha-methylcysteine, which cannot undergo beta-lyase-dependent bioactivation, was not nephrotoxic. These in vivo data show that Compound A-derived S-conjugates are nephrotoxic and that the toxicity is associated with beta-lyase-dependent bioactivation.

Regression of pulmonary lesions produced by inhaled titanium dioxide in rats

Inhaled ultrafine particles of TiO2 (TiO2-D, 20 nm particle size) lead to a greater pulmonary inflammatory response than larger pigment-grade particles (TiO2-F, 250 nm). Male Fisher 344 rats were exposed for 6 hours a day, 5 days a week, for 3 months to 1) filtered air (control); 2) TiO2-F, 22.3 mg/m3; 3) TiO2-D, 23.5 mg/m3; or 4) crystalline SiO2, a positive control particle (approximately 800 nm particle size, 1.3 mg/m3). Groups of 3-4 animals were sacrificed at 6 and 12 months following the completion of exposure. Pulmonary effects of exposure were evaluated using standard hematoxylin and eosin-stain sections, histochemical stains for collagen, and immunohistochemical assays for cell turnover. Six months after animals were exposed to SiO2, they had moderate focal interstitial fibrosis and moderately severe focal alveolitis. Animals exposed to TiO2-D had slightly less fibrosis. The least fibrosis was seen in the TiO2-F group. At 1 year after exposure, fibrosis was still present but decreased in the SiO2 group. The amount of interstitial fibrosis in the TiO2-D- and TiO2-F-treated animals had largely returned to untreated control levels, although an increased number of alveolar macrophages persisted, usually with retained particles. There was discordance between bromodeoxyuridine and proliferating cell nuclear antigen indices, most probably due to cytokine elaboration in the areas of inflammation, which may have altered the expression of proliferating cell nuclear antigens. There was no detectable fibroblast labeling at the 6-month observation and only very low levels at 12 months. Thus, although initially irritant, TiO2-induced lesions regressed during a 1-year period following cessation of exposure.

Intratracheal instillation versus intratracheal inhalation: influence of cytokines on inflammatory response

Our laboratory has developed a method of particle exposure whereby anesthetized rats intratracheally inhale, at a regulated breathing rate and pressure, an aerosolized test material. This method is capable of delivering considerable doses in a short time period and, unlike the commonly used method of intratracheal instillation, does so with an even particle distribution throughout the lung. Early studies comparing the response of male Fischer 344 rats exposed to TiO2 particles of two differing primary particle sizes showed that at similar particle doses animals exposed by the two methods showed differences in response, as measured by bronchoalveolar lavage (BAL) parameters. Building on this, we sought to study the roles that macrophage inflammatory protein-2 (MIP-2) and tumor necrosis factor alpha (TNF-alpha), two cytokines thought to have proinflammatory roles in the lung, may play in the differences observed. Increases in MIP-2 protein levels in the lavaged cells, but not the supernatant, were observed in those groups where increased polymorphonuclear cells (PMN) in the lung lavage were found, but not in those where no increase in PMN levels was observed. BAL TNF-alpha levels, measured by enzyme-linked immunosorbent assay, showed no apparent correlation with cellular or biochemical BAL parameters for either particle size or dosing method. Increases in immunocytochemical staining for TNF-alpha, compared to unexposed controls, were observed in several particle-exposed groups. Thus, it appears that increased BAL MIP-2 protein levels, but not TNF-alpha, correlate well with the inflammatory response, as measured by PMN numbers in lavaged cells, for both exposure systems.

Teratogenicity of methanol following a single oral dose in Long-Evans rats

The teratogenicity of methanol was investigated following a single oral exposure preceded by an equal volume of mineral oil to guard against local gastric irritation. Four groups of pregnant Long-Evans rats were gavaged on day 10 of gestation with the following solutions: 0.0 (n = 13), 1.3 (n = 12), 2.6 (n = 11), and 5.2 (n = 10) mL MeOH/kg. Wilson sectioning (head only), gross necropsy, and Alizarin red skeletal examinations were performed on day 20 of gestation. At 5.2 mL/kg, the dams demonstrated > 20% decrease in weight gain in comparison to the control, which was the only clinical toxic manifestation or histopathologic change noted for the dams. Methanol at all doses failed to produce any significant change in standard reproductive indices (e.g., postimplantation loss). A significant decrease in fetal body weight (11 to 19.5%), however, was associated with prenatal oral ingestion of methanol. Both internal and external examination of the fetuses demonstrated a dose-dependent increase in anomalies [0 = 0.6%, 1.3 mL/kg = 3.7%, 2.6 mL/kg = 7%, 5.2 mL/kg = 16.5% (litter percents)]. The dose-related anomalies were undescended testes, exophthalmia, and anophthalmia. Thus, acute methanol given orally produces anomalies, even when there is no apparent maternal toxic response.

Changes in surfactant protein gene expression in a neonatal rabbit model of hyperoxia-induced fibrosis

Lung injuries, including bronchopulmonary dysplasia, alter the surfactant system. We developed a newborn rabbit model of acute, followed by chronic, hyperoxic injury to study surfactant protein (SP) gene expression. Initial litters were exposed to >95% O2 until 50% died (LD50; 7-11 days old). Subsequent litters were exposed to >95% O2 for 8 days, followed by 60% O2 until 22-36 days. Controls were exposed to room air. LD50 animals displayed acute pulmonary inflammation, edema, protein leak, and surfactant dysfunction. These changes resolved, and fibrosis developed by 22 days. Whole lung SP-A mRNA expression (measured by membrane hybridization) was twice control levels at 4 days of >95% O2, with specific elevations in terminal bronchioles and type II cells at 4 days and the LD50 by in situ hybridization. Whole lung SP-B and SP-C mRNA were unchanged from control throughout exposure. However, in situ hybridization showed elevations in SP-B and SP-C mRNA in type II cells in inflamed areas at the LD50. SP mRNA alterations resolved by 22-36 days. The surfactant system recovers from acute hyperoxic injury, despite continued 60% O2 exposure.

Immunolocalization of microsomal glutathione S-transferase in rat tissues

Distribution of microsomal glutathione transferase (mGST) protein in rat tissues was investigated by immunohistochemistry. Studies on the localization of mGST are of interest because of its involvement in the detoxication and bioactivation of xenobiotics. mGST antigen was detected in the cytoplasm of some hepatocytes and in bile ducts. In kidney, focal staining of mGST was observed in distal tubules and collecting ducts. Cerebral cortical and cerebellar Purkinje neurons showed good immunoreactivity, and nuclear staining was observed in the choroid plexus. The antigen was detected in epithelial cells of respiratory bronchioles and in the crypt cells of the duodenum. Exocrine cells of the pancreas stained for mGST. Nuclear immunostaining for this protein was observed in primary spermatocytes. mGST antigen was detected in the cytoplasm of the adrenal medulla as a granular stain. Leydig and Sertoli cells in testis also stained for the antigen. Distribution of mGST protein differs from that observed with cytosolic transferases and may be important in determining cell-selective susceptibility to xenobiotics.

Pulmonary inflammatory, chemokine, and mutagenic responses in rats after subchronic inhalation of carbon black

Chronic inhalation of carbon black can produce carcinomas in rat lungs. At present the mechanisms underlying the rat lung tumor response to carbon black are unknown, although a significant role for inflammation and cell proliferation has been postulated. To investigate the processes which may contribute to development of rat lung tumors after carbon black exposure, we characterized the effects of subchronic inhalation of carbon black by rats on mutagenesis in alveolar epithelial cells, pulmonary inflammation, inflammatory cytokine/growth factor expression, and lung histopathology. Briefly, rats were exposed for 6 hr/day, 5 days/week for up to 13 weeks to 1.1, 7.1, and 52.8 mg/m3 carbon black and the effects on the lung were characterized after 6.5 and 13 weeks of exposure and 3 and 8 months of recovery. Endpoints characterized after carbon black exposure included mutation in the hprt gene of alveolar epithelial cells, changes in bronchoalveolar lavage fluid markers of lung injury and inflammation, expression of mRNA for the chemokines, MIP-2 and MCP-1, and lung histopathology. Lung burdens of carbon black were also determined. After 13 weeks of exposure to 1.1, 7.1, and 52.8 mg/m3 carbon black, lung burdens were 354, 1826, and 7861 micrograms carbon black, respectively. The lung clearance of carbon black appeared impaired after exposure to 7.1 and 52.8 mg/m3 carbon black, with the effects being more pronounced at the higher exposure level. Subchronic inhalation of 1.1 mg/m3 carbon black did not elicit any detectable adverse lung effects. A significant increase in hprt mutation frequency in alveolar epithelial cells was detected immediately after 13 weeks of exposure to 7.1 and 52.8 mg/m3 carbon black as well as after 3- and 8-month recovery periods for the group exposed to 52.8 mg/m3. No increase in hprt mutation frequency was observed for epithelial cells obtained from rats exposed to 1.1 mg/m3 carbon black. The observation that genotoxic effects (i.e., mutations) on alveolar epithelial cells occurred only after carbon black exposures which resulted in significant inflammation and epithelial hyperplasia supports the hypothesis that inflammatory cell-derives oxidants and increased cell proliferation play a role in the pathogenesis of rat lung tumors in response to carbon black.

Formulation of the purified fusion protein of respiratory syncytial virus with the saponin QS-21 induces protective immune responses in Balb/c mice that are similar to those generated by experimental infection

The feasibility of employing a vaccine composed of the purified fraction 21 of Quillaja saponaria (QS-21) and the fusion (F) protein of respiratory syncytial virus (RSV) to induce protective immune responses in the lower respiratory tract of Balb/c mice was examined. Our goal was to compare local and systemic immune responses with those induced following immunization with the protein adsorbed to aluminium hydroxide (F/ALOH) adjuvant or by experimental infection. Sera from mice vaccinated with the QS-21 formulation (F/QS-21) contained elevated anti-F protein IgG antibody titres that were dependent on the dose of QS-21 employed. Similar to the immune responses generated by experimental infection, the sera from mice vaccinated with F/QS-21 possessed greater capacity to neutralize virus infectivity that was associated with the generation of heightened complement-fixing IgG2a antibody titres. In contrast, vaccination with F/ALOH elicited systemic immune responses that were characterized by a predominance of protein-specific antibodies of the IgG1 subclass and lower neutralizing antibody titres. The capacity of F/QS-21 to facilitate local pulmonary immune responses was also examined and found to be similar to those induced by experimental infection. After virus challenge, a 90-fold increase in the number of F protein-specific antibody-secreting cells was observed and associated with the clearance of virus from the infected lungs. Moreover, elevated levels of antigen-dependent killer cell activity were detected and appeared to be mediated by class I major histocompatibility complex restricted CD8+ T cells. Additional characterization of the pulmonary immune response was performed on the cellular infiltrates obtained after bronchoalveolar lavage and on formalin-fixed lung tissue. The local protective immune responses induced after challenge of the groups immunized with F/QS-21 or infectious virus were significantly different from those elicited in naive control mice injected with adjuvant alone, or in mice immunized with F/ALOH. The cellularity of the lavage fluids from the former groups was characterized by a significantly greater percentage of lymphocytes and less neutrophils. In similar fashion histological evaluation of the lungs from mice immunized with F/QS-21 or infectious virus revealed significantly elevated local immune responses after challenge. In conclusion, the results suggest that formulation with F/QS-21 alters the qualitative and quantitative nature of the immune response to the F glycoprotein when compared with the traditional aluminium-based adjuvants.

Nephrotoxicity and hepatotoxicity of 5,6-dichloro-4-thia-5-hexenoic acid: evidence for fatty acid beta-oxidation-dependent bioactivation

5,6-Dichloro-4-thia-5-hexenoic acid (DCTH) is toxic to rat liver and kidney mitochondria and is cytotoxic to isolated rat hepatocytes. The object of this investigation was to test the hypothesis that DCTH is bioactivated in vivo by the enzymes of mitochondrial fatty acid beta oxidation and that the observed mitochondrial dysfunction is a consequence of this bioactivation. DCTH was a potent nephrotoxin and hepatotoxin in Long-Evans rats, whereas the odd-chain-length analog 6,7-dichloro-5-thia-6-heptenoic acid was not toxic. DCTH produced morphological changes in renal proximal convoluted tubules and the liver. The increases in urinary protein, glucose and blood urea nitrogen concentrations were consistent with the renal lesions. Hepatic lesions were associated with an increase in plasma glutamate-pyruvate transaminase activity, a marked infiltration of lipid and depletion of glycogen concentrations. A pronounced decrease in plasma glucose concentrations was also observed. DCTH decreased fatty acid beta oxidation by 75% and 40% in liver and kidney mitochondria, respectively, isolated from DCTH-treated rats. In addition, medium-chain acyl-coenzyme A dehydrogenase activity was reduced by 25% in rat liver mitochondria incubated with DCTH. The data presented are consistent with the hypothesis that DCTH is bioactivated by the mitochondrial fatty acid beta-oxidation system and that mitochondria are a critical cellular target in DCTH-induced toxicity.

Correlation between cadmium-induced pulmonary carcinogenicity, metallothionein expression, and inflammatory processes: a species comparison

There is sufficient evidence for pulmonary carcinogenicity of inhaled Cd compounds in rats whereas no such evidence was found in mice and hamsters; the evidence in humans has been termed limited, indicating significant species differences in pulmonary response to inhaled Cd. We hypothesized that expression of metallothionein (MT) protein in the lung after inhalation of Cd differs between species thereby providing different degrees of sequestration of Cd and protection from its effects. Rats and mice were exposed to 100 micrograms CdCl2 aerosols/m3 for 4 weeks, and the presence of MT was determined in lung and free lung cell homogenates as well as by immunocytochemistry in lung sections up to 28 days postexposure. In addition, pulmonary inflammatory, and cell proliferative responses were determined. Cd exposure significantly increased MT in homogenates of total lung in both species; however, no significant increase of MT in rat lung tissue after removal of free lung cells by lavage was found whereas MT was still significantly increased in lavaged mouse lung tissue throughout the postexposure time. In contrast, exposed rats showed significant increases in MT in the lavageable lung cells and mice did not. Histochemical analysis of lung sections revealed that mainly the epithelial cells of the bronchi, bronchioli, and alveoli of Cd-exposed mice expressed MT. Mice also exhibited a marked and sustained pulmonary inflammatory and cell proliferative response upon CdCl2 exposure which was not observed in rats. The retained Cd dose per gram lung was about 2-fold greater in mice, which is consistent with a greater deposition efficiency of inhaled Cd-aerosols in mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Importance of species differences in experimental pulmonary carcinogenicity of inhaled cadmium for extrapolation to humans

There is sufficient evidence for pulmonary carcinogenicity of inhaled cadmium (Cd) compounds in rats whereas no such evidence was found in mice and hamsters, indicating significant species differences in the pulmonary response to inhaled Cd. We hypothesized that expression of metallothionein (MT) protein in the lung after inhalation of Cd differs between species thereby providing different degrees of sequestration of Cd and protection from its effects. Rats and mice were exposed to 100 micrograms CdCl2 aerosols/m3 for 4 weeks, and the presence of MT was determined in lung and free lung cell homogenates as well as by immunocytochemistry in lung sections up to 28 days post-exposure. Cd exposure significantly increased MT in homogenates of total lung in both species; however, no significant increase of MT in rat lung tissue after removal of free lung cells by lavage was found whereas MT was still significantly increased in lavaged mouse lung tissue throughout the post-exposure time. Histochemical analysis of lung sections revealed that mainly the epithelial cells of the bronchi, bronchioli and alveoli of Cd-exposed mice expressed MT. Baseline MT levels were also greater in the lungs of mice compared to rats. The retained Cd dose per g lung was about 2-fold greater in mice. The greater MT induction upon exposure to the same inhaled Cd concentration and the greater baseline MT levels may offer an explanation for the resistance of mice towards the pulmonary carcinogenic effect of inhaled Cd.

Effects of insulin-like growth factor receptor inhibition on human melanomas in culture and in athymic mice

The role of the insulin-like growth factor (IGF) receptor in regulating the growth of melanoma cells was evaluated by examining the effect of antibody-mediated IGF receptor inhibition on the growth of four human melanoma cell lines in culture and as xenotransplants in athymic mice. All four cell lines expressed typical type I IGF receptors and an antibody to this receptor (alpha IR-3) inhibited [125I]IGF-I binding. However, the cell lines varied widely in their in vitro responsiveness to IGF-I and alpha IR-3: in the WM 373 and WM 852 cell lines, IGF-I stimulated cell replication and alpha IR-3 inhibited this response, whereas in the WM 239-A and WM 266-4 cell lines neither the growth factor nor the antibody affected growth. A wide variation was also observed in the effect of the antibody on the growth of the different cell lines as xenotransplants but this qualitatively correlated with the responses observed in vitro: alpha IR-3 treatment significantly inhibited the growth of the WM 373 and WM 852 xenotransplants but did not inhibit the growth of the WM 239-A or WM 266-4 xenotransplants and may even have had a slight stimulatory effect. These results indicate that the IGF receptor pathway is a functional regulator of the in vivo growth of some melanomas and that this is reflected in the activity of this pathway as determined in vitro. These findings suggest that therapies aimed at inhibiting the IGF pathway may be beneficial in treating some melanomas.

Selective vulnerability and early progression of hippocampal CA1 pyramidal cell degeneration and GFAP-positive astrocyte reactivity in the rat four-vessel occlusion model of transient global ischemia

Selective, delayed-onset vulnerability of hippocampal CA1 pyramidal cells has been reported as a unique phenomenon in man and the rat four-vessel occlusion (4-VO) model of global ischemia. This has become of great interest for clarification of CA1 pathophysiology and pharmacological intervention after global ischemia. Studies of pathophysiology and pharmacotherapy appear to be impeded by variability in specific criteria and duration of 4-VO ischemia for producing selective CA1 and differential CA1-CA3 damage. The goals of this study were to: (1) develop specific criteria for 4-VO ischemia to ensure selective, bilaterally symmetrical CA1 pyramidal cell damage, (2) examine the effects of 15 min of ischemia on concomitant CA1 cell necrosis and presence of remaining and/or "viable" neurons postischemia, (3) compare 15 and 30 min of ischemia on differential vulnerability of CA1-CA3 subfields, and (4) evaluate the effects of 15 min of ischemia on CA1 pyramidal cell necrosis and glial fibrillary acidic protein (GFAP)-positive astrocyte reactivity in CA1. After 15 min of ischemia, hippocampal pyramidal cell damage was well delineated, with CA1 severely damaged, but leaving CA3 virtually intact. In contrast, 30 min of ischemia produced severe CA1 and less severe CA3 necrosis. Histological evaluations across Days 1, 3, 6, and 14 indicated a significant delayed onset of CA1-CA3 cell necrosis by Day 3. Counting of remaining cells indicated a detectable loss of some large pyramidal neurons even 1 day after ischemia. Compared to controls, there was a differential increase in GFAP-positive astrocytes in CA1-CA3 after ischemia. The results provided quantitative data on the effects of specific 4-VO criteria and durations on: (1) selective CA1 cell necrosis, (2) differential CA1-CA3 cell vulnerability, (3) presence of postischemic remaining and/or viable neurons, and (4) prospect of a "therapeutic window" for pharmacological treatment of CA1 neuronal injury.

Effect of IL-1 on experimental bone/bone-marrow metastases

Bone metastasis is a common event and a major cause of morbidity in cancer patients. The hematopoietic marrow of the bones, rather than the bone tissue per se, is the target organ in bone metastasis. In the bone marrow, IL-1 induces the release of hematopoietic growth factors that may affect tumor-cell growth. We treated groups of mice with rhuIL-1 alpha to examine its role in the establishment of experimental bone/bone-marrow metastasis. We found that injection of 2 micrograms of rhuIL-1 alpha 24 hr prior to, simultaneously with or 24 hr after the injection of 10(4) B16 melanoma cells into the left cardiac ventricle of mice resulted in a 2-fold increase in the average number of colonized bones per mouse. GM-CSF is produced by bone-marrow stromal cells in response to IL-1, and its receptor has been found on tumor cells, including melanoma cells. However, the administration of rmuGM-CSF to mice by either multiple injections or continuous infusion did not affect the number of colonized bones. Many of the biologic effects of IL-1 are mediated by prostaglandins. Treatment of mice with 100 micrograms of indomethacin, a potent inhibitor of prostaglandin synthesis, prior to the injection of rhuIL-1 alpha, prevented the increase in number of bone metastases. To determine whether constitutive productions of IL-1 and/or prostaglandins are involved in the pathogenesis of bone/bone marrow metastasis, we treated mice with antimouse IL-1 alpha neutralizing antibodies, rhuIRAP (an inhibitor of IL-1 activity) or indomethacin. We found no difference in the average number of colonized bones per mouse between treated and control mice. We conclude that exogenous administration of IL-1 enhances experimental bone/bone-marrow metastases, and that this phenomenon is mediated through prostaglandins. However, neither the constitutive production of IL-1 nor that of prostaglandins appear to play a role in the pathogenesis of bone/bone-marrow metastasis in our murine model system.

Nephrotoxicity of the glutathione and cysteine conjugates of 2-bromo-2-chloro-1,1-difluoroethene

The mercapturate S-(2-bromo-2-chloro-1,1-difluoroethyl)-N-acetyl-L-cysteine, which is apparently derived from the halothane degradation product 2-bromo-2-chloro-1,1-difluoroethene, is excreted in urine. S-(2-Bromo-2-chloro-1,1-difluoroethyl)glutathione (BCDFG) and S-(2-bromo-2-chloro-1,1-difluoroethyl)-L-cysteine (BCDFC) are putative intermediates in the metabolism of 2-bromo-2-chloro- 1,1-difluoroethene and are analogs of nephrotoxic and cytotoxic S-haloalkyl glutathione and cysteine conjugates. The objective of the research was to study the nephrotoxicity and cytotoxicity of 2-bromo-2-chloro-1,1-difluoroethene-derived S-conjugates. BCDFG and BCDFC were nephrotoxic in Fischer 344 rats and caused diuresis, increases in urine glucose and protein concentrations, in blood urea nitrogen concentrations, in kidney/body weight percentages and in serum glutamate-pyruvate transaminase activities. Both S-conjugates also produced severe morphological changes in the kidneys, especially in the proximal tubules. Morphological changes indicative of hepatotoxicity were seen in some animals given BCDFG and BCDFC. Both BCDFG and BCDFC were cytotoxic to LLC-PK1 cells, as shown by lactate dehydrogenase release into the medium. The cytotoxicity of BCDFG was blocked by the gamma-glutamyltransferase inhibitor acivicin, and the cytotoxicity of both BCDFG and BCDFC was blocked by the cysteine conjugate beta-lyase inhibitor aminooxyacetic acid. Also, S-(2-bromo-2-chloro-1,1-difluoroethyl)-DL-alpha-methylcysteine, which can not be metabolized by beta-lyase, was not toxic to LLC-PK1 cells. These in vivo and in vitro data provide evidence that BCDFG and BCDFC are nephrotoxic and that their toxicity is dependent on renal bioactivation by cysteine conjugate beta-lyase.

Incidence and distribution of experimental metastases in mutant mice with defective organ microenvironments (genotypes Sl/Sld and W/Wv)

Mice carrying mutations at the Sl (steel) and W (dominant white spotting) loci develop abnormalities on 3 migratory embryonic stem cell populations: hematopoietic stem cells, neural crest-derived melanocytes, and primordial germ cells. Transplantation experiments have indicated that the Sl locus affects the microenvironment where stem cells migrate, proliferate, and differentiate, while the W locus affects the migratory cells themselves. The Sl locus encodes for a multipotent growth factor known as stem cell factor. The W locus encodes the c-kit protein tyrosine kinase receptor whose ligand is the stem cell factor. We have investigated the incidence and organ distribution of experimental metastases after systemic intra-arterial injection of B16-G3.26 melanoma cells into mutant Sl/Sld and W/Wv mice. Both mutant mouse strains had a markedly lower incidence of ovarian metastases when compared with their congenic +/+ mice. In contrast to the rare colonization of the ovaries, Sl/Sld and W/Wv mice developed metastases in the myocardium, kidney, and stomach--anatomic sites that were infrequently or never affected in their congenic nonmutant mice. The only organs in which the average number of metastatic colonies differed between Sl/Sld and W/Wv mice were the bone marrow and kidneys. The average number of colonized bones per mouse in the Sl/Sld group was 5.0 +/- 3.1 (SD), compared with 12.7 +/- 5.3 in the W/Wv group. The average number of metastatic nodules in the kidneys of Sl/Sld mice was 24.6 +/- 9, while W/Wv mice had 15.5 +/- 2.5. Mutant mice with multiple metastatic nodules in the kidneys, heart, and stomach were also found to have forestomach papillomas, an enlarged duodenum, kidney abnormalities, and small body size. The results of this study provide useful information on potential mechanisms of interaction of metastatic cells with their target organs, and suggest that there are additional organ defects associated with the mutations in the Sl and W loci. They also document the importance of mutant mice in metastasis research.

The effects of exposure to dietary nickel and zinc upon humoral and cellular immunity in SJL mice

We are interested in potential interactions between environmental trace metal exposures and immune function. In particular, we have wondered whether dietary exposure to nickel and zinc cations can influence T and B cell proliferation and function. To study this question, we fed SJL female mice supplemental nickel and zinc sulfate from 4-8 weeks of age, and immunized the animals intraperitoneally (i.p.) with keyhole limpet hemocyanin (KLH) at 8 weeks. Eight days later, we measured antibody responses to KLH. Both IgG and IgM antibody responses to KLH were significantly depressed in vivo in the nickel fed animals (p less than 0.005). In vitro antigenic responsiveness to KLH of splenocytes from nickel fed animals was also depressed compared with control and zinc supplemented animals (p less than 0.002). This altered antigenic responsiveness persisted even after cells had been cultured for 5 days in standard media. The zinc supplemented diets did not seem to affect antibody responsiveness and proliferation. The proliferative responses of B cells to the mitogen lipopolysaccharide (LPS) were significantly depressed in Ni fed mice, but were not affected in the zinc fed animals. T cell mitogenic responses to concanavalin A were not affected in the nickel fed animals, and were enhanced in zinc fed animals. We conclude that dietary exposure to certain trace metals may induce persisting alterations in immunity in this animal model.

Vascular anatomy and organ-specific tumor growth as critical factors in the development of metastases and their distribution among organs

We have examined with 19 tumor cell lines the discrete roles that vascular anatomy and tumor-cell-organ-affinity play in the development of metastases and their distribution among organs. Spontaneous metastases of B16-G3.26 melanoma cells from a primary tumor growing in the foot pad of mice, or experimental metastases 21 days after intravenous tumor-cell injection resulted in tumor colonies only in the lungs. In contrast, when the lung microvasculature was bypassed, and the same cells given by systemic intra-arterial (s.i.a.) injection, large tumor colonies developed selectively in the ovaries, adrenal glands and bones, but rarely in the lungs. When animals injected i.v. were allowed to live with lung metastases for a long period of time, small tumor colonies began to develop in extra-pulmonary organs with a distribution identical to that seen after s.i.a. injection. Seven murine tumor cell lines (previously characterized by their ability to colonize primarily the lungs after i.v. injection) and 7 of the 8 studied human tumor cell lines colonized different specific extra-pulmonary organs after s.i.a. injection, frequently producing metastatic syndromes commonly described in patients with cancer, but rarely seen in animal models of metastasis. These results suggest that metastatic cells, even those capable of colonizing specific organs, do not freely circulate in the blood stream and lodge in specific tissues. In contrast, the cells must establish a vascular route of access to the target organ, e.g., through the systemic circulation from metastatic tumors in the lungs. Two cell lines considered to be tumorigenic but non-metastatic failed to colonize the lungs or extra-pulmonary organs after i.v. injection, but readily colonized specific organs after s.i.a. injection. Thus, tumor cells considered to be non-metastatic may be indeed metastatic if they are provided with vascular access to an organ more congenial to their growth requirements.

Carcinogenicity of diethylstilbestrol in the Wistar rat: effect of postnatal oral contraceptive steroids

Diethylstilbestrol (DES) has been associated with vaginal neoplasia and malformations in humans. We have studied a test population of 504 female Wistar rats given diethylstilbestrol at from 0.0 to 0.5 mg/kg maternal body weight on days 18, 19, and 20 of gestation. Animals were euthanized in extremis, or at 2 years of age. The incidence of vaginal epithelial tumors was dose related. The types of epithelial tumors of the vagina were adenocarcinoma, squamous cell carcinoma, and mixed carcinoma, containing discrete adenomatous and squamous components. The incidence of vaginal epithelial tumors was determined to be dose related: rats exposed to 0 mg DES/kg maternal weight had an incidence of 0.6% (1 of 167 rats); 0.1 mg/kg, 4.1%; and 0.5 mg/kg, 4.3% (6 of 140); 25 mg/kg, 1.6% (1 of 63); and 50 mg/kg, 11.5% (3 of 26). Tumors of other reproductive tissues (mammary gland, ovary, oviduct, cervix, or uterus) demonstrated no discernible DES dose-response relationship. There was no oncogenic effect of postnatal administration of oral contraceptives (0 oral contraceptives, 31.25 micrograms/kg diet ethynylestradiol, and 31.25 micrograms/kg diet norethindrone or 104 micrograms/kg diet ethynylestradiol and 31.25 micrograms/kg diet norethindrone). Thus, vaginal tumors can be induced in a dose-related manner in the rat following in utero DES exposure. Oral contraceptive treatment did not increase the risk of neoplasia.

Gross and microscopic changes in the viscera induced by photodynamic therapy applied to the lower abdomen of intact rats

Photodynamic therapy (PDT) is a promising approach to the treatment of cancer. Preferential retention of the photosensitizer by malignant tissue has been considered a hallmark of this treatment modality. However, photosensitivity can be observed in normal, non-neoplastic tissues, and the present study investigated the effects of PDT treatment on the abdomen of intact rats. A circular region (1 cm diameter) on the shaved abdomen of Fischer rats, pretreated 24 h prior with Photofrin II, was irradiated for 30 min at 632 nm. Control animals received either photoradiation or Photofrin II administration. Subsequent lesions were observed in the irradiated skin, its associated abdominal wall, and the underlying gut in rats receiving Photofrin II and laser irradiation. All tissues were not equally sensitive to PDT treatment. Gut lesions were consistently more severe than were skin and abdominal wall injuries. By 24 hr after treatment, the gut manifested a transmural hemorrhagic necrosis, while the irradiated skin and abdominal wall were edematous, with an inflammatory infiltrate in the dermis and around occasional swollen myocytes. These results indicate that superficial lesions induced by PDT may not be reliable indicators of the extent of deeper PDT tissue damage. Further, it may be possible to take advantage of this discrepancy in tissue sensitivity and treat deep tissues through less sensitive superficial tissues.

Immune modulation in the guinea pig using cortisone acetate

Cortisone acetate was administered to a group of guinea pigs (Cavia porcellus) at 0 (control), 20 (low) or 200 (high) mg/kg. Steroid was given daily for two individual 7 day periods, separated by 7 days of no treatment. The effects of this steroid on body weight gain, thymic weight, total and differential leukocyte counts, serum antibody titer against a bacterin, dermal hypersensitivity response to a sensitizing agent and histological evaluation of lymphoid and other tissues were evaluated. Significant differences in body weight gain (p less than 0.05) and thymic weight (p less than .01) were noted. For total leukocyte count, no significant difference among treatment groups at individual time points was noted (p greater than .10), while significant differences were seen in lymphocyte and neutrophil counts (p less than .01). A significant difference in antibody titer among the treatment groups was observed (p less than .01). For the dermal hypersensitivity response, there was no consistent pattern among the treatment groups in gross (macroscopic) skin reactions. Microscopically, differences were seen in the inflammatory response among the treatment groups. Histologically, steroid related changes were seen in thymus, spleen, lymph node and liver. At necropsy, 24 of 40 animals had lesions of focal necrotizing hepatitis. Three affected animals died and remaining animals showed no clinical illness. The cause of the necrotizing hepatitis could not be determined by culture, special stains, electron microscopy, serology or by attempts at transmission with affected liver samples.

Ultrasound contrast for hepatic tumors using IDE particles

Iodipimide ethyl ester (IDE) can be formulated as dense spherical particles with narrow diameter distribution. When IDE particles are injected intravenously, the Kupffer cells of the hepatic sinusoids accumulate particles within 10 to 20 minutes, after which the clearance and excretion of IDE takes place. During the uptake phase, the dense particles act as scattering sites, increasing the echogenicity of normal liver tissue. In comparison, tumors and other lesions remain at pre-injection echogenicity, as they lack Kupffer cells and therefore do not retain particles. This report provides initial studies of contrast enhancement in rabbit livers with implanted VX2 tumors, scanned in vivo and evaluated ex vivo using pulse-echo techniques. The distribution of particles within hepatic lobules may explain why the observed echogenicity is greater than that predicted by single-particle backscatter theory. Directions for future improvements are discussed.

Central nervous system lesions in the Wistar rat fetus following direct fetal injections of cadmium

During embryogenesis, maternal administration of cadmium (Cd) produces teratogenic effects, including hydrocephalus (HC), whereas later in gestation (during the fetal period), such effects have not been reported. Since there is little placental transfer of Cd late in gestation, such differences in response could be due to a lower Cd concentration in the fetus compared with the embryo after maternal Cd exposure, or could be due to a decreased sensitivity of the fetal central nervous system (CNS) to Cd. To test the susceptibility of the late gestational CNS to Cd, day 19 (sperm plug = day 0) rat fetuses were directly injected i.p. with CdCl2 (165, 100, 50 nmoles/fetus in 5 microliters saline). All fetuses in one horn were treated with Cd, while fetuses in the other horn were treated with saline. Fetuses were collected on day 21, grossly examined, weighed, fixed in Bouin's fixative, and later razor sectioned. Cd did not affect fetal viability or body weight. However, Cd caused a dose-dependent increase in hydrocephalus, with the total number of fetuses showing moderate to severe HC being 0/45, 0/11, 6/10, and 18/20 for controls, low, medium, and high doses, respectively. Mild HC was noted in one control and two low Cd fetuses. Brain necrosis was correlated with hydrocephalus, being observed in 0/45, 0/11, 5/10, and 16/20 fetuses, respectively. In medium-dose fetuses without HC or brain necrosis, extravasation of erythrocytes was noted histologically within the cortical parenchyma, suggesting that hemorrhaging may lead to brain necrosis and hydrocephalus in Cd-exposed fetuses. Thus, the fetal CNS is susceptible to the toxic effects of Cd.

Use of Vicryl (polyglactin 910) mesh to limit epidural scar formation after laminectomy

A variety of substances have been used at laminectomy sites to prevent postoperative epidural scarring. Free grafts of autologous subcutaneous fat are commonly used both clinically and experimentally. The free fat grafts usually survive, but decrease in size by about 50%. Postoperatively, subcutaneous seroma has been observed with the use of fat grafts, as well as recurrent symptoms of neural compression by the graft that required additional operations. When compared to the use of free grafts after laminectomy in dogs, Vicryl mesh produced slightly more scarring, but consistently less than that observed in control animals. The Vicryl mesh was resorbed by a minimal chronic inflammatory response over about 45 days. Seven of 11 fat-grafted zones showed signs of necrosis, at times with a greater collection of inflammatory cells than that associated with the Vicryl mesh. Of the 4 fat-grafted zones that showed good survival, 2 had gross evidence of neural compression. No surgical zone treated with Vicryl mesh exhibited evidence of neural compression. In view of these results, the use of Vicryl mesh at laminectomy sites may be a safer method of limiting postoperative epidural scar formation.

Lymphocytic infiltration and cytotoxicity under hypoxic conditions in the EMT6 mouse mammary tumor

Infiltration of lymphocytes, neutrophils and macrophages was evaluated in hypoxic and well-oxygenated areas of the EMT6 mouse mammary adenocarcinoma, by in vivo staining with the fluorescent dye Hoechst 33342 followed by cell sorting on the basis of fluorescence intensity. Tumors were grouped by days post-injection (days 11-14, 15-17 and 20-27). As lymphocytes are the only host cell population in this tumor model to possess lytic activity against EMT6 tumor cells, the ability of sensitized T lymphocytes to lyse syngeneic EMT6 cells was examined under conditions of varying oxygen concentrations. Infiltrating lymphocytes were detected to the same extent in cell fractions from both areas in all tumors. In contrast, neutrophils were found in significantly higher percentages in the hypoxic population than in the well-oxygenated cell fraction of all but the largest tumors. Macrophages were present in significantly higher percentages in the well-oxygenated fraction than in the hypoxic fraction of day-11 to -14 tumors. Extreme radiobiological hypoxia (0% O2) resulted in a significant decrease in T-cell-mediated lysis of EMT6 tumor cells, compared to lysis in room air (20% O2), but lysis was not impaired under conditions of mild radiobiological hypoxia (1% O2). Our study indicates that host-cell infiltration into areas of differing oxygenation may be quantitated via in situ Hoechst staining followed by cell sorting; in the EMT6 tumor, lymphocytes appear to infiltrate hypoxic areas to the same extent as well-oxygenated areas, and T-lymphocyte killing of syngeneic tumor cells is significantly reduced, although still present, under these hypoxic conditions.

Pathogenesis of vertebral metastasis and epidural spinal cord compression

The authors have studied the sequential events in the process of vertebral metastasis that result in spinal cord compression. Different tumor cell lines were injected into the systemic arterial circulation of syngeneic or nude mice, and they were killed at timed intervals after injection or when they became paraplegic. The following observations were made. The tumor cells lodged and grew in the hematopoietic bone marrow of the vertebrae. Cancer cells in the vertebral marrow cavity invaded into the spinal canal through the foramina of the vertebral veins rather than destroying the cortical bone. Tumor cell lines that grew in an infiltrative fashion migrated toward a posterior location in the spinal canal, and compressed the spinal cord from a posterior direction. Tumor cell lines that grew as compact tumors formed a tumor mass at the same location from which the cells emerged from the vertebra, and compressed the cord predominantly from an anterior direction. Radiographic evidence of vertebral metastasis was a late event, and commonly associated with significant compression of the cord and extraosseous tumor. These experimental findings may help to establish better diagnostic and treatment strategies for patients with metastatic disease of the spine.

Immunization of cotton rats with the fusion (F) and large (G) glycoproteins of respiratory syncytial virus (RSV) protects against RSV challenge without potentiating RSV disease

A formalin-inactivated respiratory syncytial virus (RSV) vaccine tested 22 years ago failed to protect infant vaccinees against RSV infection or disease. Instead, lower respiratory tract disease was enhanced during subsequent infection by RSV. Enhancement of pulmonary pathology is also observed when cotton rats are immunized with formalin-inactivated RSV and subsequently infected with this virus. A major question that must be addressed for each new paramyxovirus vaccine is whether the immunogen possesses the capacity to potentiate disease. In the present study, we evaluated a newly developed purified F and G glycoprotein vaccine over a wide dosage range for immunogenicity, efficacy and capacity to potentiate pulmonary pathology in cotton rats. In addition, a formalin-inactivated RSV vaccine, which served as a positive control for enhancement of pulmonary pathology, was evaluated simultaneously. The results of these comparisons indicate that the purified F and G glycoprotein vaccine was highly immunogenic and was efficacious even in animals that developed low levels of serum-neutralizing antibodies. Furthermore, the F and G vaccine did not induce potentiation of pulmonary pathology. In contrast, formalin-inactivated RSV potentiated RSV pulmonary histopathology, but there was a sparing of potentiation at high and low doses. Both the formalin-inactivated RSV and purified F and G preparations induced a high level of serum antibodies capable of binding to purified F and G glycoproteins but both sets of antibodies had significantly reduced neutralizing activity. These results are encouraging because they suggest that purified paramyxovirus glycoproteins might be used safely as a vaccine.(ABSTRACT TRUNCATED AT 250 WORDS)

Reversible uranyl fluoride nephrotoxicity in the Long Evans rat

Severity and duration of renal injury produced by low levels of uranyl fluoride (UO2F2) were examined in the rat. Rats received multiple ip injections of UO2F2 (cumulative dose: 0.66 or 1.32 mg U/kg body wt). Renal injury was characterized histologically by cellular and tubular necrosis of pars recta of proximal tubule (S2 and S3), with less severe cellular injury to thick ascending limb of loop of Henle and collecting tubule. Injury was evident when renal uranium levels were between 0.7 and 1.4 micrograms U/g wet kidney and was most severe when renal uranium burden was between 3.4 and 5.6 micrograms U/g. Repair of injury was rapid, with complete restoration within 35 days after exposure. Associated with injury were abnormalities in renal function, including impaired tubular reabsorption, proteinuria, and enzymuria, which appeared temporally related, to variable degrees, to progression of renal injury. Thus, reversible renal injury occurs in the rat at levels of uranium in kidney below the present Nuclear Regulatory Commission standard of 3 micrograms U/g kidney for renal injury in humans.

A murine model of experimental metastasis to bone and bone marrow

Bone is a common site of metastasis in human cancer. A major impediment to understanding the pathogenesis of bone metastasis has been the lack of an appropriate animal model. In this paper, we describe an animal model in which B16 melanoma cells injected in the left cardiac ventricle reproducibly colonize specific sites of the skeletal system of mice. Injection of 10(5) cells resulted in melanotic tumor colonies in most organs, including the skeletal system. Injection of 10(4) or fewer cells resulted in experimental metastasis almost entirely restricted to the skeletal system and ovary. In contrast, i.v. injection of 10(5) cells resulted in tumor colonies in the lung only. Left cardiac injection of 10(2) cells caused bone colonization, but the same number of cells injected i.v. did not colonize the lung. The number of bones with tumor colonies increased with increasing number of cells injected. Melanotic tumor colonies in the bone were characteristically distributed in the metaphysis of long bones and in the periphery of flat bones. Most animals developed paraplegia due to spinal cord compression by bony metastasis to the spine. Tumor colonization of bone occurred only in regions of bone containing hematopoietic bone marrow. This suggests that the injected tumor cells lodge, survive in the hematopoietic bone marrow environment, and grow to destroy adjacent bone. This experimental model of metastasis to bone will facilitate future studies of the pathophysiology and treatment of bone and bone marrow metastasis.

Myelin basic protein and magnetic resonance imaging for diagnosing radiation myelopathy

The identification of radiation myelopathy using biochemical assays and imaging techniques has not previously been accomplished but has clear clinical application. Measurement of myelin basic protein (MBP) in the cerebrospinal fluid (CSF) and visualization of the spinal cord using magnetic resonance imaging (MRI) gives a potentially accurate diagnosis of radiation myelopathy. Female New Zealand white rabbits were irradiated to the thoracic spinal cord with single doses of 15-45 Gy. Animals receiving higher doses (greater than or equal to 22 Gy) generally demonstrated an early paresis (4-8 weeks) that temporarily improved, and then progressed to complete paralysis by 14-18 weeks. MBP levels in the CSF became strikingly elevated to 100-1000 times the normal value. Subsequent, experiments in which rabbits were serially assessed for MBP levels demonstrated a transient elevation, which corresponded to the transient paresis, followed by dramatic elevations concurrent with the onset of paralysis. Magnetic resonance imaging (MRI) of the irradiated spinal cord showed a geographically distinct region of abnormality that corresponded to the radiation field. Histopathology demonstrated demyelination, focal astrocytosis, erythrodiapedesis, and perineuronal edema in the irradiated sections. It appears that MBP levels in the CSF reflect not only radiation-induced myelopathy but also transient demyelination, and that MRI may have the potential to indicate the region of damage.

Anesthetic-induced corneal lesions in developmentally sensitive rats

Developmental critical periods for the induction of abnormalities by exposure to exogenous substances need not be confined to the early embryonic stage of organogenesis. The combination of ketamine hydrochloride and xylazine, two commonly used anesthetic agents, resulted in a corneal epithelial calcium deposition in 84% of rat pups whose exposure was limited to a single injection during the third postnatal week only. Concurrent exposure to ketamine hydrochloride, xylazine, and yohimbine, an alpha 2 adrenergic receptor antagonist, resulted in corneal lesions in only 6% of rat pups so exposed. The etiology is presently not understood but may involve interference with neurally directed corneal development. Corneal desiccation may also play a role. Altered drug metabolism, and toxic interactions resulting from a changing oxygen or light milieu are less likely etiologic mechanisms. Aspects of corneal development and mechanisms by which drugs can interact with and disturb normal maturational sequences can now be approached.

Operant behavior in transition reflects neonatal exposure to cadmium

Male Long-Evans rats were injected with 0, 1, 3, or 6 mg/kg of cadmium chloride on the first day of life. Animals free of morphological stigmata at weaning were selected for study. Tissue concentrations of cadmium and operant behavior under various fixed-ratio (FR) schedules of reinforcement were evaluated when these rats were adults. Dose-related increases in cadmium were present in the brains, livers, and kidneys. Dose-related differences in behavior were most evident during the transition from fixed ratio 25 (FR 25 or 25 responses/reinforcer) to FR 75. An inverted U describes the relationship between response output during the transition to FR 75 and cadmium chloride dose response output increased at 3 mg/kg and decreased at 6 mg/kg. The rate decreases were not correlated with weight loss that appeared after some of the animals exposed to 6 mg/kg reached 60 days of age. Challenge doses of d-amphetamine revealed no interaction between neonatal exposure to cadmium and d-amphetamine. The occurrence of alterations in operant behavior in animals that appeared normal on a number of preweaning evaluations suggests that operant behavior in transition was sensitive to subtle effects not observed with other commonly used tests. The data provide evidence for delayed effects in the adult that are due to neonatal exposure to cadmium.

Changes in hamster hepatic cytochrome P-450, ethoxycoumarin O-deethylase, and reduced NAD(P): menadione oxidoreductase following treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin. Partial dissociation of temporal and dose-response relationships from elicited toxicity

The temporal and dose-related characteristics of hepatic enzymes induced in the hamster by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) were examined. Male Syrian golden hamsters received a single intraperitoneal injection of TCDD at a dose of 0-500 micrograms/kg. At various times up to 35 days, a number of variables were determined and compared: whole body, liver, and thymus weights; hepatic concentrations of cytochrome P-450 (P-450); and activities of 7-ethoxycoumarin O-deethylase (ECOD) and reduced NAD(P): menadione oxidoreductase (NMOR). Increased liver weights and decreased thymus weights were observed to be dose related. At day 7 following treatment, the approximate ED50 values for these responses were 15 and 100 micrograms/kg respectively. The ED50 values for the increase in hepatic P-450 concentrations and activities of ECOD and NMOR ranged from 0.5 to 2.0 micrograms/kg. At 10 and 500 micrograms/kg, NMOR activity remained maximally induced for up to 35 days. This was also the case for P-450 and ECOD activity at a dose of 10 micrograms/kg. At 500 micrograms/kg, both P-450 and ECOD demonstrated an induction up to day 4 followed by a decrease to near control levels by day 14. This decrease appeared to correlate with changes in hepatic morphology. These results demonstrate a dissociation of the induction of these hepatic enzymes from TCDD-induced lethality, in this species.