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J D Laskin

Publications and source records attributed to J D Laskin.

At least 37 records · Page 2Linked to original sources
PubMed1998

Role of nitric oxide in acetaminophen-induced hepatotoxicity in the rat.

Acetaminophen is a mild analgesic and antipyretic agent known to cause centrilobular hepatic necrosis at toxic doses. Although this may be due to a direct interaction of reactive acetaminophen metabolites with hepatocyte proteins, recent studies have suggested that cytotoxic mediators produced by parenchymal and nonparenchymal cells also contribute to the pathophysiological process. Nitric oxide is a highly reactive oxidant produced in the liver in response to inflammatory mediators. In the present studies we evaluated the role of nitric oxide in the pathophysiology of acetaminophen-induced liver injury. Treatment of male Long Evans Hooded rats with acetaminophen (1 g/kg) resulted in damage to centrilobular regions of the liver and increases in serum transaminase levels, which were evident within 6 hours of treatment of the animals and reached a maximum at 24 hours. This was correlated with expression of inducible nitric oxide synthase (iNOS) protein in these regions. Hepatocytes isolated from both control and acetaminophen-treated rats were found to readily synthesize nitric oxide in response to inflammatory stimuli. Cells isolated from acetaminophen-treated rats produced more nitric oxide than cells from control animals. Production of nitric oxide by cells from both control and acetaminophen-treated rats was blocked by aminoguanidine, a relatively specific inhibitor of iNOS. Arginine uptake and metabolism studies revealed that the inhibitory effects of aminoguanidine were due predominantly to inhibition of iNOS enzyme activity. Pretreatment of rats with aminoguanidine was found to prevent acetaminophen-induced hepatic necrosis and increases in serum transaminase levels. This was associated with reduced nitric oxide production by hepatocytes. Inhibition of toxicity was not due to alterations in acetaminophen metabolism since aminoguanidine had no effect on hepatocyte cytochrome P4502E1 protein expression or N-acetyl-p-benzoquinone-imine formation. Taken together, these data demonstrate that nitric oxide is an important mediator of acetaminophen-induced hepatotoxicity.

Acetaminophen↗
PubMed1998

Inhaled nitric oxide primes lung macrophages to produce reactive oxygen and nitrogen intermediates.

Inhaled nitric oxide is a selective pulmonary vasodilator used for the treatment of pulmonary hypertension. The potential adverse effects of inhaled nitric oxide are unknown and represent the focus of the present studies. Whereas inhalation of nitric oxide (10 to 100 ppm, 5 h) by Balb/c mice had no effect on the number or type of cells recovered from the lung, a dose-related increase in bronchoalveolar lavage protein was observed, suggesting that nitric oxide induces alveolar epithelial injury. To determine if this was associated with altered alveolar macrophage activity, we quantified production of reactive oxygen and nitrogen intermediates by these cells. Interferon-gamma, alone or in combination with lipopolysaccharide (LPS), induced expression of inducible nitric oxide synthase (iNOS) protein and nitric oxide production by alveolar macrophages. Cells from mice exposed to 20 to 100 ppm nitric oxide produced significantly more nitric oxide and expressed greater quantities of iNOS than cells from control animals. Superoxide anion production and peroxynitrite generation by alveolar macrophages were also increased after exposure of mice to nitric oxide. This was correlated with increased antinitrotyrosine antibody binding to macrophages in histologic sections. Taken together, these data demonstrate that inhaled nitric oxide primes lung macrophages to release reactive oxygen and nitrogen intermediates. Increased production of these mediators by macrophages following inhalation of nitric oxide may contribute to tissue injury.

Administration, Inhalation↗
PubMed1998

Increased nitric oxide synthase in the lung after ozone inhalation is associated with activation of NF-kappa B.

Acute inhalation of ozone is associated with a inflammatory response characterized by the accumulation of macrophages at sites of tissue injury. These cells, along with resident alveolar epithelial cells, become activated and release cytotoxic and proinflammatory mediators, such as nitric oxide (.NO), that we speculate contribute to toxicity. In these studies we analyzed mechanisms regulating increased .NO synthase activity in lung macrophages and type II cells after ozone inhalation. Brief exposure of rats to ozone (2 ppm for 3 hr) resulted in an increase in .NO production by alveolar macrophages as well as type II cells in response to the inflammatory mediators lipopolysaccharide and interferon gamma. These effects were apparently due to increased expression of inducible .NO synthase (iNOS) protein and mRNA, which were evident in vitro and in situ in histologic sections. .NO production and iNOS protein expression by both macrophages and epithelial cells were blocked by pyrrolidine dithiocarbamate (PDTC), an agent that inhibits activity of nuclear transcription factor kappa B (NF-kappa B). Cells from ozone-treated animals were less sensitive to the effects of PDTC than cells from control animals. Using electrophoretic mobility shift assays, we measured NF-kappa B binding activity in nuclear extracts of cells from control and ozone-exposed animals. Treatment of rats with ozone resulted in a time-dependent increase in NF-kappa B binding activity in both cell types, reaching a maximum in cells isolated 12 to 24 hr after ozone inhalation. Taken together, these data suggest that changes in the activity of NF-kappa B signaling are important in the response of lung macrophages and type II epithelial cells to cytokines after ozone inhalation.

Animals↗
PubMed1997

Arginine metabolism in keratinocytes and macrophages during nitric oxide biosynthesis: multiple modes of action of nitric oxide synthase inhibitors.

Nitric oxide is an important cellular mediator produced in keratinocytes and macrophages from arginine by the enzyme nitric oxide synthase during inflammatory reactions in the skin. We found that gamma-interferon stimulated nitric oxide production and the expression of inducible nitric oxide synthase in both cell types. However, macrophages produced more nitric oxide and nitric oxide synthase protein, and at earlier times than keratinocytes. Keratinocytes treated with gamma-interferon took up more arginine than macrophages; however, they were less efficient in metabolizing this amino acid and exhibited reduced nitric oxide synthase enzyme activity. In both cell types, the nitric oxide synthase inhibitors, N(G)-monomethyl-L-arginine (NMMA), L-N5-(iminoethyl)ornithine, L-canavanine, and N(omega)-nitro-L-arginine, as well as lysine, ornithine, and homoarginine markedly reduced arginine uptake. In contrast, N(omega)-nitro-L-arginine methyl ester and N(omega)-nitro-L-arginine benzyl ester were poor inhibitors of arginine uptake, while aminoguanidine had no effect on uptake of arginine by the cells. Moreover, NMMA was found to inhibit simultaneously arginine uptake and nitric oxide synthase enzyme activity in both cell types, whereas aminoguanidine only affected nitric oxide synthase activity. No major differences were observed between keratinocytes and macrophages. Taken together, these data demonstrate that, although keratinocytes and macrophages both synthesize nitric oxide, its production is regulated distinctly in these two cell types. Furthermore, in these cells, nitric oxide synthase inhibitors such as NMMA exhibit at least two sites of action: inhibition of nitric oxide synthase and cellular uptake of arginine.

Animals↗
PubMed1996

5-Fluorouracil suppresses nitric oxide biosynthesis in colon carcinoma cells.

Nitric oxide is an important cellular mediator that plays a role in regulating cellular proliferation of both normal and tumor cells. In the present study, we characterized nitric oxide production by the human colon adenocarcinoma cell line DLD-1 and examined the effects of 5-fluorouracil (5-FUra), an antimetabolite effective against colon tumors, on nitric oxide production. IFN-gamma was found to be a potent inducer of nitric oxide production in DLD-1 cells. This effect was dependent on L-arginine and blocked by the nitric oxide synthase inhibitors NG-monomethyl-L-arginine, nitroarginine, and aminoguanidine. Production of nitric oxide by DLD-1 cells was due to the expression of the inducible (type II) form of nitric oxide synthase. mRNA for the nitric oxide synthase was present in both untreated and IFN-gamma-stimulated cells, as determined by RT-PCR, suggesting that expression of enzyme is regulated posttranscriptionally. Treatment of DLD-1 cells with concentrations of 5-FUra that are not growth inhibitory or cytotoxic strongly inhibited their ability to express nitric oxide synthase and produce nitric oxide in response to IFN-gamma. This effect was not reversed with thymidine, indicating that inhibition of nitric oxide production was due to incorporation of 5-FUra into RNA. However, pretreatment of DLD-1 cells with 5-FUra before stimulation with IFN-gamma also suppressed nitric oxide production. Thus, inhibition of nitric oxide production was not due directly to incorporation of 5-FUra into the mRNA for nitric oxide synthase. Taken together, these data suggest that inhibition of nitric oxide biosynthesis in colon tumor cells by 5-FUra may underlie, at least in part, the efficacy of this antitumor agent.

Antimetabolites, Antineoplastic↗
PubMed1996

Inhibition of ozone-induced nitric oxide synthase expression in the lung by endotoxin.

Inhalation of the pulmonary irritant ozone is associated with an accumulation of macrophages in the lung. These cells, along with type II epithelial cells, are activated to release increased quantities of hydrogen peroxide and nitric oxide, two reactive mediators that have been implicated in tissue injury. In the present studies we determined whether pretreatment of rats with bacterially derived endotoxin, which modulates oxidant levels in tissues, could abrogate the effects of ozone on lung injury and nitric oxide production. Acute exposure of rats to ozone (2 parts per million, 3 h) resulted in nitric oxide production in the lung as measured by electron paramagnetic resonance spin trapping. This was correlated with expression of inducible nitric oxide synthase (iNOS) mRNA in the lung as determined by in situ hybridization. Particularly high levels of iNOS were evident in alveolar macrophages and type II cells. Alveolar macrophages isolated from ozone-treated rats also expressed increased iNOS mRNA and protein as measured by Northern and Western blotting, respectively, and produced more nitric oxide compared with cells from air-exposed animals. Treatment of rats with endotoxin (5 mg/kg, intravenously), 30 min prior to ozone, was found to abrogate ozone-induced increases in iNOS mRNA and protein expression, as well as nitric oxide production by alveolar macrophages. This was associated with a reduction in ozone-induced tissue injury as determined by levels of lung lavage fluid protein. Ozone inhalation also resulted in a reduction in intracellular glutathione in alveolar macrophages, an effect that was blocked by endotoxin administration. Taken together, these data provide evidence that the protective effects of endotoxin against ozone-induced injury are mediated, at least in part, by alterations in levels of lung oxidants and antioxidants.

Animals↗
PubMed1996

Role of nitric oxide in hematosuppression and benzene-induced toxicity.

It is becoming increasingly apparent that nitric oxide plays a multifunctional role in regulating inflammatory processes in the body. Although nitric oxide and its oxidation products are cytotoxic toward certain pathogens, they can also cause tissue injury and suppress proliferation. Cytokines and growth factors released at sites of inflammation or injury stimulate both immune and nonimmume cells to produce nitric oxide. Nowhere in the body is this more detrimental than in the bone marrow, for the continuous production of hematopoietic precursors is essential for normal blood cell maturation. Our laboratories have discovered that, in response to inflammatory mediators, bone marrow cells readily produce nitric oxide. Nitric oxide production is enhanced by hematopoietic growth factors including interleukin-3, macrophage colony stimulating factor, and granulocyte-macrophage colony-stimulating factor. When bone marrow cells produce nitric oxide, hematopoiesis is impaired, an effect that is potentiated by colony-stimulating factors. Treatment of mice with benzene, which suppresses bone marrow cell development, was found to markedly enhance the ability of bone marrow cells to produce nitric oxide in response to inflammatory mediators alone and in combination with hematopoietic growth factors. Taken together, these data suggest that nitric oxide may be an important mediator of benzene-induced bone marrow suppression.

Animals↗
PubMed1995

Lymphocyte-mediated nitric oxide production by rat endothelial cells.

Lymphocyte migration from the blood to sites of tissue injury is mediated, in part, through the interaction of these cells with endothelial cells lining the vessel walls. The ability of endothelial cells to produce nitric oxide may be important in this process. We found that the addition of the nonspecific lymphocyte activators lipopolysaccharide (LPS) or concanavalin A (Con A) to rat hepatic endothelial cell cultures from control or endotoxemic rats markedly enhanced the ability of these cells to produce nitric oxide. In contrast, wheat germ agglutinin (WGA) and phytohemagglutinin (PHA) had no effect on nitric oxide release. Coculture of endothelial cells with lymphocyte-rich preparations of rat thymocytes or splenocytes stimulated endothelial cell nitric oxide production. This response was enhanced by LPS or Con A and to a lesser extent by WGA or PHA. In contrast to endothelial cells, thymocytes and splenocytes did not produce nitric oxide either in the presence or absence of lymphocyte mitogens. Increased production of nitric oxide by endothelial cells in response to lymphocytes and lymphocyte mitogens was due, at least in part, to increased expression of protein for an inducible form of nitric oxide synthase, as measured by Western blotting. Stimulation of endothelial cell nitric oxide production by thymocytes and splenocytes was inhibitable by the specific nitric oxide synthase inhibitor NG-monomethyl-L-arginine and dependent on cell-cell contact. Thus, nitric oxide production by endothelial cells was reduced when the lymphocytes were physically separated from the endothelial cells using cell culture inserts. We hypothesize that nitric oxide released by endothelial cells increases vascular permeability, thereby allowing the extravasation of lymphocytes into the surrounding tissue, a process that may be important in inflammation, tissue injury, and/or wound healing.

Amino Acid Oxidoreductases↗
PubMed1995

Distinct biochemical responses of hepatic macrophages and endothelial cells to platelet-activating factor during endotoxemia.

Acute endotoxemia is associated with activation of hepatic macrophages and endothelial cells. These cells release a variety of inflammatory mediators that have been implicated in tissue injury. In the present studies, we analyzed the biochemical responses of these cells to platelet-activating factor (PAF), a lipid autacoid released during hepatic inflammatory responses. To induce acute endotoxemia, rats were injected intravenously with lipopolysaccharide (LPS). Using the calcium sensitive fluorescent indicator dye Indo-1, we found that PAF induced a rapid and transient increase in intracellular calcium in both hepatic macrophages and endothelial cells. Induction of acute endotoxemia resulted in an increase in the amount of calcium mobilized by both cell types. Although endothelial cells from control rats were less responsive to PAF than macrophages, these cells were more sensitive to in vivo endotoxin. PAF was also found to cause a rapid decrease in intracellular pH in hepatic macrophages that was quantified by fluorescence image analysis using the pH sensitive dye SNAFL-calcein. This decrease occurred more rapidly in macrophages from endotoxemic rats. In cells from both control and endotoxemic rats, the effects of PAF on intracellular pH were inhibited by the specific PAF antagonist triazolam. In contrast to hepatic macrophages, PAF had no effect on intracellular pH in endothelial cells from either control or endotoxemic rats. Ligand binding studies demonstrated that both hepatic macrophages and endothelial cells possess high affinity binding sites for PAF. Macrophages expressed 6- to 7-fold more binding sites/cell than endothelial cells and exhibited a higher Kd. Whereas treatment of rats with LPS had no effect on the Kd for PAF binding to macrophages or on the number of binding sites, a significant increase in both of these receptor characteristics was observed in endothelial cells. Taken together, the present data suggest that the biochemical responses of endothelial cells and macrophages to PAF are distinct. Furthermore, cellular activation induced by PAF in endothelial cells appears to be independent of changes in intracellular pH.

Acute Disease↗
PubMed1995

Distinct actions of benzene and its metabolites on nitric oxide production by bone marrow leukocytes.

Benzene is a widely used industrial solvent known to cause bone marrow depression. This is associated with increased production of reactive oxygen metabolites and nitric oxide by bone marrow phagocytes, which have been implicated in hematotoxicity. Benzene metabolism to phenolic intermediates appears to be an important factor in bone marrow toxicity. In the present studies, we compared the effects of benzene and several of its metabolites on nitric oxide production by murine bone marrow leukocytes. Bone marrow cells readily produced nitric oxide in response to the inflammatory mediators lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma). Treatment of mice with benzene (800 mg/kg), or its metabolites hydroquinone (100 mg/kg), 1,2,4-benzenetriol (25 mg/kg), or p-benzoquinone (2 mg/kg), at doses that impair hematopoiesis, sensitized bone marrow leukocytes to produce increased amounts of nitric oxide in response to LPS and IFN-gamma. Granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF) augmented bone marrow leukocyte production of nitric oxide induced by inflammatory mediators. Benzene, as well as its metabolites, markedly increased the sensitivity of the cells to both GM-CSF and M-CSF. Cells from hydroquinone- or 1,2,4-benzenetriol-treated mice were significantly more responsive to the inflammatory cytokines and growth factors than cells isolated from benzene- or p-benzoquinone-treated mice, suggesting that the phenolic metabolites of benzene are important biological reactive intermediates. Because nitric oxide suppresses cell growth and can be metabolized to mutagens and carcinogens, the ability of benzene and its metabolites to modulates its production in the bone marrow may be important in their mechanism of action.

Animals↗
PubMed1995

Inhibition of macrophages with gadolinium chloride abrogates ozone-induced pulmonary injury and inflammatory mediator production.

Acute inhalation of toxic doses of ozone (O3) induces macrophage accumulation in the lung and the release of cytotoxic and proinflammatory mediators. To evaluate the role of macrophages and their mediators in the pathophysiologic response of the lung to O3, we examined the effects of the macrophage inhibitor, gadolinium chloride (GdCl3), on O3-induced inflammation, mediator production, and lavage fluid protein levels. Rats were pretreated with GdCl3 (7 mg/kg, intravenously) or control 24 h prior to exposure to air or O3 (2 parts per million, 3 h). Animals were killed 48 h after exposure. GdCl3 pretreatment of rats was found to abrogate O3-induced increases in the number of cells, as well as the amount of protein recovered in bronchoalveolar lavage fluid. Following GdCl3 pretreatment of rats, lung lavage cells consisting of > 90% macrophages were found to produce significantly less nitric oxide and express less inducible nitric oxide synthase (iNOS) when compared to cells from rats exposed to O3. O3-induced alterations in superoxide anion production by alveolar macrophages, both in vitro and in situ, were also attenuated by GdCl3 pretreatment of rats. In addition, increases in tumor necrosis factor alpha (TNF-alpha) and fibronectin in lung tissue induced by O3 were reduced. Taken together, these data provide support for the hypothesis that macrophages contribute to the pathogenesis of O3-induced lung injury.

Amino Acid Oxidoreductases↗
PubMed1995

Hepatic nitric oxide production following acute endotoxemia in rats is mediated by increased inducible nitric oxide synthase gene expression.

In the present studies, we analyzed the effects of acute endotoxemia on hepatocyte nitric oxide production and functional activity. Treatment of rats with 5 mg/kg of lipopolysaccharide (LPS), which induces acute endotoxemia, caused an increase in nitric oxide production in the liver, as measured by electron paramagnetic spin trapping, which was evident within 6 hours. This was associated with expression of inducible nitric oxide synthase (iNOS) messenger (m) RNA in hepatocytes and in sinusoidal cells throughout the liver lobule. Acute endotoxemia also caused alterations in hepatic structure, including hypertrophy, vacuolization, and chromosomal emargination, however these changes were not apparent for 24 to 48 hours. Hepatocytes isolated from endotoxemic rats released increased amounts of nitric oxide, measured by nitrite production, in response to interferon gamma (gamma-IFN) alone or in combination with LPS, tumor necrosis factor alpha, macrophage-colony stimulating factor, granulocyte/macrophage-colony stimulating factor, or hepatocyte growth factor. These results show that hepatocytes are sensitized by acute endotoxemia to respond to inflammatory mediators and growth factors. Increased nitrite production by hepatocytes was due to increased expression of iNOS mRNA and protein and was correlated with the time following induction of acute endotoxemia. Thus, cells isolated 48 hours after induction of acute endotoxemia released significantly more nitrite than cells recovered after 6 hours, a response that was not due to alterations in hepatocyte viability. Hepatocytes isolated from endotoxemic rats also exhibited a marked increase in proliferative capacity when compared with cells from control rats. Nitric oxide production by hepatocytes in vitro was associated with inhibition of cell growth and protein synthesis, which was reversed by the nitric oxide synthase inhibitor, NG-monomethyl-l-arginine (L-NMMA). Agarose gel electrophoresis showed extensive cytoplasmic DNA fragmentation in hepatocytes treated with LPS and gamma-IFN, a characteristic of apoptosis, which was also reversed by L-NMMA. These results, together with our findings that treatment of rats with an inhibitor of nitric oxide synthase partially reversed the structural alterations in the liver associated with acute endotoxemia suggest that nitric oxide may contribute to the pathophysiologic response to this bacterially derived toxin.

Acute Disease↗
PubMed1995

Flow cytometry reveals subpopulations of murine epidermal cells that are refractory to induction of cytochrome P-4501A1 by beta-naphthoflavone.

Topical application of beta-naphthoflavone to CD-1 mice induced an 87-fold increase in epidermal 7-ethoxyresorufin O-dealkylation activity per cell and a many-fold increase in epidermal cytochrome P-4501A1 (CYP1A1) concentration. Flow cytometric analysis of individual epidermal cells from acetone-treated and beta-naphthoflavone-treated mice using a monoclonal antibody for CYP1A1 indicated that 50% to 60% of the isolated epidermal cells were refractory to beta-naphthoflavone induction of CYP1A1. Examination of the differences between responsive and nonresponsive epidermal cells from beta-naphthoflavone-treated mice revealed that 70% of the low CYP1A1-containing cells (noninduced) separated by flow cytometry were basal cells and only 12% were suprabasal differentiated cells. In contrast, about 50% of the high CYP1A1-containing induced cells separated by flow cytometry from the epidermis of mice treated with beta-naphthoflavone were suprabasal cells and 35% were basal cells. These results indicate that topical application of beta-naphthoflavone increased the level of CYP1A1 in about 80% of the separated suprabasal cells and in about 35% of the separated basal cells.

Animals↗
PubMed1995

Inhibition of epidermal growth factor-stimulated EGF receptor tyrosine kinase activity in A431 human epidermoid carcinoma cells by polyamines.

Polyamines--putrescine, spermidine, and spermine--are ubiquitous cellular components that play an important role in cell growth and differentiation. Using A431 cells, a cell line that overexpresses the epidermal growth factor (EGF) receptor, we found that polyamines modulate EGF-mediated growth inhibition. The natural polyamine, putrescine, was the most effective, followed by diamines containing lower and higher methylene bridging between the amino groups. To understand the mechanism, we examined the effects of polyamines on EGF-mediated signal transduction in A431 cells. All three polyamines partially inhibited EGF-receptor tyrosine kinase activity in a dose-dependent manner. The maximal inhibition was 75% with spermidine. Polyamine effects were exerted 12-16 h after treatment, although HPLC analysis revealed uptake of polyamines within 1 h. Homologues of putrescine had no significant effect on tyrosine kinase activity, indicating structural specificity of naturally occurring polyamines in this process. Amine oxidase inhibitors did not alter spermidine and spermine-mediated effects, suggesting that the inhibition of tyrosine kinase activity was not a consequence of the oxidative metabolism of polyamines. Difluoromethylornithine, a specific inhibitor of polyamine biosynthesis, did not affect EGF receptor tyrosine kinase activity. Polyamines also had no effect on EGF receptor levels or EGF-EGF receptor high-affinity binding, indicating that they are not competitive inhibitors of the EGF receptor tyrosine kinase. Our results suggest that polyamine action in A431 cells involves modulation of EGF receptor signal transduction pathways.

Biogenic Polyamines↗
PubMed1994

Role of nitric oxide in hepatic injury following acute endotoxemia.

Hepatocytes from control and endotoxemic rats were cultured for 40 hours in 96-well dishes in medium containing 0-5 micrograms/ml of lipopolysaccharide in the presence or absence of 50 U/ml IFN gamma. Nitric oxide production was quantified by the accumulation of nitrite in the culture medium by the Greiss reaction. Hepatocyte proliferation and protein synthesis were measured by (3H)thymidine (TdR) and (3H)leucine (Leu) incorporation, respectively. Results are the mean +/- standard error of triplicate wells from four experiments.

Acute Disease↗
PubMed1994

Enhanced production of nitric oxide by bone marrow cells and increased sensitivity to macrophage colony-stimulating factor (CSF) and granulocyte-macrophage CSF after benzene treatment of mice.

Nitric oxide is a short-lived reactive mediator that inhibits bone marrow (BM) cell proliferation induced by granulocyte-macrophage colony-stimulating factor (GM-CSF). The present studies show that nitric oxide also inhibits macrophage colony-stimulating factor (M-CSF)-induced growth of mouse BM cells, an effect that was dependent on the presence of an inflammatory mediator and blocked by the nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (L-NMA). Treatment of mice with the hematotoxicant benzene (800 mg/kg, intraperitoneally, two times per day, for 2 days) resulted in a significant increase in nitric oxide production by BM cells stimulated with lipopolysaccharide (LPS) and interferon gamma alone or in combination with M-CSF or GM-CSF. Cells from benzene-treated mice also displayed increased sensitivity to the growth-promoting effects of M-CSF and GM-CSF. These results suggest that benzene treatment of mice primes BM cells to inducers of nitric oxide. Northern blot analysis showed that this was, at least in part, caused by increased expression of mRNA for inducible nitric oxide synthase (iNOS). Surprisingly, treatment of mice with L-NMA was found to cause a depression in BM cell proliferation and to potentiate benzene-induced decreases in BM cellularity and increases in nitric oxide production. L-NMA administration also augmented nitric oxide production by BM cells. These data indicate that L-NMA is hematotoxic and suggest that it may have actions distinct from inhibition of nitric oxide synthase in the BM.

Animals↗