Antibodies to tumor necrosis factor alfa attenuate hepatic necrosis and inflammation caused by chronic exposure to ethanol in the rat

Tumor necrosis factor (TNF)alpha, a pivotal cytokine involved in inflammation, is produced primarily by Kupffer cells in the liver. It has been shown that inactivation of Kupffer cells prevents alcohol-induced liver injury; therefore, the purpose of this study was to determine if neutralizing anti-TNF-alpha antibody is also effective. Male Wistar rats were exposed to ethanol (11 to 12 g x kg(-1) x d[-1]) continuously for up to 4 weeks via intragastric feeding using an enteral feeding model. Before ethanol exposure, polyclonal anti-mouse TNF-alpha rabbit serum was injected (2.0 mg/kg intravenously). There were no significant differences in body weight, mean ethanol concentration, or cyclic patterns of ethanol in urine when ethanol- and ethanol plus antibody-treated groups were compared. Expression of TNF-alpha and macrophage inflammatory protein 2 (MIP-2) messenger RNA (mRNA), determined using reverse transcription-polymerase chain reaction, was three- to four-fold higher in livers of ethanol-treated rats than in those of rats fed an ethanol-free, high-fat control diet. In addition, MIP-2 levels were also elevated when detected by Northern blot analysis. Anti-TNF-alpha antibody did not affect expression of mRNA for interleukin (IL) 1alpha, IL-6, transforming growth factor beta1, or TNF-alpha. However, MIP-2 mRNA expression, which is regulated by TNF-alpha, was decreased significantly by anti-TNF-alpha antibody treatment. Serum aspartate transaminase levels were elevated in ethanol-treated rats to 136 +/- 12 IU/L after 4 weeks but only reached 90 +/- 5 IU/L (P < .05) in rats treated with anti-TNF-alpha antibody. The hepatic inflammation and necrosis observed in ethanol-fed rats were attenuated significantly by antibody treatment, and steatosis was not. These results support the hypothesis that TNF-alpha plays an important role in inflammation and necrosis in alcohol-induced liver injury and that treatment with anti-TNF-alpha antibody may be therapeutically useful in this disease.

Molecular regulation of IL-6 activation by asbestos in lung epithelial cells: role of reactive oxygen species

IL-6 has been characterized as a pleiotropic cytokine with multiple biologic activities, but its induction and role in asbestos diseases have not been studied. Asbestos fibers were found to stimulate IL-6 expression and secretion in pulmonary type II-like epithelial A549 cells as well as in normal human bronchial epithelial cells. IL-6 induction was dependent on the intracellular redox-oxidative state, since intracellular hydroxyl scavengers and N-acetylcysteine, a precursor of glutathione, abrogated IL-6 secretion by asbestos or H2O2. IL-6 induction paralleled increased DNA binding activity to the nuclear factor-kappa B (NF-kappa B)- and NF-IL-6-recognized sites in the IL-6 promoter. The NF-kappa B and NF-IL-6 DNA binding proteins were immunochemically characterized as a heterodimer p65/p50 and a homodimer C/EBP beta, respectively. Stimulation of DNA binding activity to the NF-kappa B and NF-IL-6 binding sites of the IL-6 promoter by asbestos or H2O2 were inhibited by tetramethylthiourea, a hydroxyl radical scavenger. The role of local IL-6 production in the pathophysiologic processes of fiber-induced lung disorders was examined. Although less active than fibroblast growth factor, human rIL-6 also stimulated lung fibroblast growth, as evidenced by increased [3H]thymidine incorporation. Furthermore, elevated IL-6 levels were found in bronchoalveolar lavage fluids from patients diagnosed with lung fibrosis and work-related histories of long term asbestos exposure. Taken together, the results suggest that asbestos-induced oxidative stress is involved in the activation of NF-kappa B and NF-IL-6 transcription factors, which recognize the IL-6 promoter. The resulting increase in IL-6 expression may be involved in both inflammatory and fibrotic processes in the lung.

Molecular regulation of IL-6 activation by asbestos in lung epithelial cells: role of reactive oxygen species

IL-6 has been characterized as a pleiotropic cytokine with multiple biologic activities, but its induction and role in asbestos diseases have not been studied. Asbestos fibers were found to stimulate IL-6 expression and secretion in pulmonary type II-like epithelial A549 cells as well as in normal human bronchial epithelial cells. IL-6 induction was dependent on the intracellular redox-oxidative state, since intracellular hydroxyl scavengers and N-acetylcysteine, a precursor of glutathione, abrogated IL-6 secretion by asbestos or H2O2. IL-6 induction paralleled increased DNA binding activity to the nuclear factor-kappa B (NF-kappa B)- and NF-IL-6-recognized sites in the IL-6 promoter. The NF-kappa B and NF-IL-6 DNA binding proteins were immunochemically characterized as a heterodimer p65/p50 and a homodimer C/EBP beta, respectively. Stimulation of DNA binding activity to the NF-kappa B and NF-IL-6 binding sites of the IL-6 promoter by asbestos or H2O2 were inhibited by tetramethylthiourea, a hydroxyl radical scavenger. The role of local IL-6 production in the pathophysiologic processes of fiber-induced lung disorders was examined. Although less active than fibroblast growth factor, human rIL-6 also stimulated lung fibroblast growth, as evidenced by increased [3H]thymidine incorporation. Furthermore, elevated IL-6 levels were found in bronchoalveolar lavage fluids from patients diagnosed with lung fibrosis and work-related histories of long term asbestos exposure. Taken together, the results suggest that asbestos-induced oxidative stress is involved in the activation of NF-kappa B and NF-IL-6 transcription factors, which recognize the IL-6 promoter. The resulting increase in IL-6 expression may be involved in both inflammatory and fibrotic processes in the lung.

Pro-inflammatory cytokines and interleukin 6 in the renal response to bacterial endotoxin

Pro-inflammatory cytokines, including tumour necrosis factor alpha (TNF-alpha), interleukin (IL)-1 and IL-6 are thought to play important roles in the pathophysiology of chronic kidney disorders, including glomerulonephritis. In particular, IL-6 has received considerable attention as it appears at high concentrations to promote the progression of renal disease while at lower levels may be involved in regulating repair mechanisms. As such, cytokine profiles have been examined in the kidney by either examining secretion from isolated kidney cells or quantitating plasma and urinary levels in experimental models of glomerulonephritis. To examine the cytokine responses within the kidney, without the contribution of other organ systems, we used semi-quantitive polymerase chain reaction (RT-PCR) analysis and a recently developed kidney slice culture model from tissues of mice treated with combinations of endotoxin and neutralizing antibodies against TNF-alpha. The expression of IL-6, in addition to other pro-inflammatory cytokine genes, was increased by endotoxin treatment and reduced by pretreatment with neutralizing antibodies to TNF-alpha. Immunohistochemical staining revealed that IL-6 was expressed primarily in mesangial cells. Urinary IL-6 was also increased in endotoxin-treated mice and was inhibited by treatment with neutralizing TNF-alpha antibodies. Kinetics of the kidney-specific cytokine responses indicated that increase in TNF-alpha occurred initially, followed by IL-1 beta and finally IL-6. Furthermore, addition of TNF-alpha to glomerular mesangial cells induces IL-6 secretion. Taken together, these studies indicate that, like in the liver, a cytokine response occurs in the kidney from bacterial endotoxin and that TNF-alpha acts as a primary cytokine capable of stimulating additional cytokines, including IL-6.

Arsenic can mediate skin neoplasia by chronic stimulation of keratinocyte-derived growth factors

Although numerous epidemiological studies have shown that inorganic arsenicals are human skin carcinogens, there is currently no accepted mechanism for its action or an established animal model for its study. We observed increased mRNA transcripts and secretion of keratinocyte growth factors, including granulocyte macrophage-colony stimulating factor (GM-CSF) and transforming growth factor-alpha (TGF-alpha) and the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) in primary human epidermal keratinocytes cultured in the presence of low micromolar concentrations of sodium arsenite. Total cell numbers, as well as c-myc expression and incorporation of [3H]thymidine, both indicators of cell proliferation, were also elevated in keratinocyte cultures treated with sodium arsenite. As an in vivo model, the influence of arsenic on mouse skin tumor development was studied in transgenic TG.AC mice which carry the v-Ha-ras oncogene, and can serve as a genetically initiated model for skin carcinogenesis. Following low-dose application of 12-O-tetradecanoyl phorbol-13-acetate (TPA), a marked increase in the number of skin papillomas occurred in transgenic mice receiving arsenic in the drinking water as compared to control drinking water. Papillomas did not develop in arsenic-treated transgenic mice that had not received TPA or arsenic-treated wild-type FVB/N mice, suggesting that arsenic is neither a tumor initiator or promoter but rather an enhancer. Injection of anti-GM-CSF antibodies following application of TPA in transgenic mice reduced the number of papillomas. Consistent with that observed in human keratinocyte cultures, increases in GM-CSF and TGF-alpha mRNA transcripts were found within the epidermis of arsenic-treated mice when compared to controls within 6 weeks of treatment. These results suggest that arsenic enhances papilloma development via the chronic stimulation of keratinocyte-derived growth factors and represents the first example of a chemical carcinogen that acts in this manner. These studies suggest that in vitro studies with human keratinocyte cultures examined in conjunction with TG.AC transgenic mice can provide a useful model for examining the tumor enhancing properties of environmental chemicals.

Antibodies to tumor necrosis factor alpha prevent increases in cell replication in liver due to the potent peroxisome proliferator, WY-14,643

Several structurally dissimilar hypolipidemic drugs, plasticizers and halogenated hydrocarbons induce peroxisomes in hepatocytes, and cause hepatocellular adenoma and carcinoma in rats and mice. The mechanism by which these agents act is unknown, although recent studies have suggested a link between increased cell proliferation and hepatic cancer caused by peroxisome proliferators. Here, we demonstrate that neutralizing antibodies to tumor necrosis factor alpha (TNF alpha) block increases in protein kinase C and cell proliferation due to [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio]acetic acid (WY-14,643), a hypolipidemic drug and potent peroxisome proliferator that causes tumors. WY-14,643 moderately elevated the level of TNF alpha mRNA in the liver. TNF alpha was detected immunohistochemically exclusively in Kupffer cells. These results demonstrate that WY-14,643 acts as an indirect mitogen on hepatocytes via TNF alpha. We propose that the Kupffer cell, a major source of TNF alpha in the liver, is involved in the mechanism of the mitogenic effect of WY-14,643.

Induction of early-immediate genes by tumor necrosis factor alpha contribute to liver repair following chemical-induced hepatotoxicity

We and others have shown that tumor necrosis factor alpha (TNF-alpha) expression is increased in the livers of experimental animals following exposure to the chemical hepatotoxin, carbon tetrachloride (CCl4). Because TNF-alpha is involved in mediating inflammatory responses, its elevated expression is presumed to be associated with potentiating hepatotoxicity and/or aiding in liver repair processes. To study the role of TNF-alpha in chemical-induced hepatotoxicity, mice were administered neutralizing antibodies to TNF-alpha before administration of low, but hepatotoxic, doses of CCl4. Antibody treatment prevented CCl4-mediated increases in early-immediate gene expression associated with liver regeneration, including expression of c-jun and c-fos proto-oncogenes, as well as DNA binding of the activator protein-1 (AP-1) nuclear transcription factor. Hepatocyte proliferation following CCl4 treatment was also reduced in anti-TNF-alpha antibody-treated mice, as evidenced by a lack of proliferating cell nuclear antigen (PCNA) staining. Antibody treatment slightly delayed liver repair processes, as evidenced by extending the period in which plasma liver enzyme levels were increased and hepatocellular necrosis could be observed. Consistent with the above observations, injection of recombinant TNF-alpha into control mice induced rapid expression of c-jun and c-fos proto-oncogenes. Taken together, these results indicate that TNF-alpha positively modulates liver recovery following CCl4 exposure presumably by stimulating early-immediate genes involved in hepatic mitogenesis, a phenomenon also observed following partial hepatectomy.

Asbestos induction of nuclear transcription factors and interleukin 8 gene regulation

Proinflammatory cytokines and chemotactic peptides are strongly implicated as mediators of the pathophysiologic responses of asbestosis and other chronic inflammatory lung diseases. Recent studies in our laboratory have demonstrated that asbestos fibers stimulate lung epithelial cells to produce interleukin-8 (IL-8), the major neutrophil chemoattractant in the lung. The mechanisms by which asbestos regulates IL-8 expression were studied using the pulmonary type II-like epithelial cell line A549. Membrane permeable hydroxyl scavengers inhibited asbestos induced IL-8 expression. Using A549 cells transfected with the -546 IL-8 construct linked to a chloramphenicol acetyl transferase reporter gene, we have shown that these antioxidants directly inhibited asbestos-stimulated IL-8 promoter-dependent transcription. Asbestos fibers as well as reactive oxygen species generating systems hypoxanthine-xanthine oxidase and hydrogen peroxide stimulated DNA binding activity to the regulatory elements in the IL-8 promoter, binding sites of nuclear factor (NF)-kappaB- and NF-IL-6-like transcription factors. Asbestos-inducible DNA binding activity was partially inhibited by tetramethylthiourea, a hydroxyl radical scavenger. IL-8 secretion was also suppressed by staurosporine, an inhibitor of protein kinase C, and by inhibitors of tyrosine kinase such as herbimycin A and genistein. The suppression paralleled the effect of these inhibitors on asbestos-induced DNA binding to the NF-kappaB- and NF-IL-6-like binding sites of the IL-8 promoter. Taken together, the results suggest that asbestos-induced redox changes and phosphorylation events, mediated by staurosporine-sensitive and tyrosine kinase(s), activate nuclear proteins which recognize the NF-kappaB/NF-IL-6 binding sites of the IL-8 promoter and contribute to the regulation of IL-8 gene expression.

Arsenic induces overexpression of growth factors in human keratinocytes

Although epidemiological studies have shown that inorganic arsenicals are human skin carcinogens and induce hyperproliferation and hyperkeratosis, there is currently no known mechanism for their action or an established animal model for its study. We observed increased mRNA transcripts and secretion of keratinocyte growth factors, including granulocyte macrophage-colony stimulating factor (GM-CSF) and transforming growth factor-alpha (TGF alpha) and the proinflammatory cytokine tumor necrosis factor-alpha in primary human epidermal keratinocytes cultured in the presence of low micromolar concentrations of sodium arsenite. Treatment with sodium arsenite resulted in a significant increase in cell proliferation, as indicated by increases in cell numbers, c-myc gene expression, and incorporation of [3H]thymidine into cellular DNA. Studies of transcriptional regulation indicate that the rate of GM-CSF mRNA transcription is increased, while the elevated TGF alpha is likely the results of message stabilization. While a number of cytokine regulatory networks exist in the skin, studies utilizing neutralizing antibodies against the growth factors of interest indicate that inhibition of the arsenic-induced increase in TGF alpha results in a corresponding decrease in the gene expression and secretion of GM-CSF. The present studies demonstrate that growth-promoting cytokines and growth factors are induced in keratinocytes following treatment with arsenic and could play a significant role in arsenic-induced skin cancer.

Role of endotoxin in tumor necrosis factor alpha expression from alveolar macrophages treated with urban air particles

The effects of urban air and diesel particles on inflammatory cytokine gene expression, tumor necrosis factor alpha (TNF-alpha) in particular, were studied in rat alveolar macrophages. TNF-alpha, interleukin (IL)-1, IL-6, cytokine-induced neutrophil chemoattractant (CINC), and macrophage inflammatory protein (MIP)-2 gene expression and TNF-alpha secretion were increased in cells treated with 50 to 200 micrograms/mL of urban air particles in a concentration-related manner. There was no cytokine induction by diesel particles at any of the concentrations tested. Cytokine expression was not related to reactive oxygen species since antioxidants, such as catalase, TMTU, or DMSO, had no effect on TNF-alpha secretion. However, cytokine induction by urban air particles was completely prevented by polymyxin B, an antibiotic capable of neutralizing bacterial lipopolysaccharide (LPS) activities. Furthermore, LPS was detected on the urban air particles, but not on diesel particle. These results suggest that activation of cytokine gene expression and secretion in rat alveolar macrophages by urban air particles is due to the presence of endotoxin on the particles.

Alterations in fetal thymic and liver hematopoietic cells as indicators of exposure to developmental immunotoxicants

Recent studies indicate that immune development in humans and other species may be altered after perinatal exposure to immunotoxic environmental contaminants. However, limited information is available regarding appropriate tests that may adequately detect developmental immunotoxic compounds. Experiments in which pregnant laboratory rodents were exposed to a variety of immunotoxic environmental agents indicate that fetal thymus and liver immune cells may be quantitatively and qualitatively altered by immunotoxicant exposure and, thus, may serve as sensitive markers of developmental immunotoxicant exposure. In particular, depression of fetal thymic cell counts appears to be a common event following gestational exposure to immunotoxicants that produce this response in adult animals. Total hematopoietic cell counts in fetal liver, however, may be a poor indicator of immunotoxicant exposure. Altered marker expression in both fetal thymus and liver appears to be a highly sensitive indicator of gestational immunotoxicant exposure. Together, these reports suggest that immune tests with high predictability for immunosuppression in adults may also be appropriate for the detection of developmental immunotoxic agents.

Alterations in fetal thymic and liver hematopoietic cells as indicators of exposure to developmental immunotoxicants

Recent studies indicate that immune development in humans and other species may be altered after perinatal exposure to immunotoxic environmental contaminants. However, limited information is available regarding appropriate tests that may adequately detect developmental immunotoxic compounds. Experiments in which pregnant laboratory rodents were exposed to a variety of immunotoxic environmental agents indicate that fetal thymus and liver immune cells may be quantitatively and qualitatively altered by immunotoxicant exposure and, thus, may serve as sensitive markers of developmental immunotoxicant exposure. In particular, depression of fetal thymic cell counts appears to be a common event following gestational exposure to immunotoxicants that produce this response in adult animals. Total hematopoietic cell counts in fetal liver, however, may be a poor indicator of immunotoxicant exposure. Altered marker expression in both fetal thymus and liver appears to be a highly sensitive indicator of gestational immunotoxicant exposure. Together, these reports suggest that immune tests with high predictability for immunosuppression in adults may also be appropriate for the detection of developmental immunotoxic agents.

Dermatotoxic chemical stimulate of c-jun and c-fos transcription and AP-1 DNA binding in human keratinocytes

In many organ/tissues rapid and transient increases in early-immediate gene responses, such as those that encode for the AP-1 family of transcription factors, occur in response to exogenous stimuli. Activation of AP-1, in turn, helps regulate the expression of genes involved in cell growth, inflammatory responses, and repair processes. In the present studies, we demonstrate that increases in AP-1 DNA binding activity, as well as c-jun and c-fos mRNA levels, occur in human keratinocytes in response to diverse dermatotoxic chemicals, including phenol and arsenic as well as phorbol ester, the latter employed as a positive control. The AP-1 DNA binding complex has affinity for the consensus AP-1 sequence but not the CRE2 binding sequence of the proenkephalin promoter or the NF kappa B consensus sequence indicating that the response is relatively specific. The binding complex is composed of Jun:Fos heterodimers, including Jun B and Jun D. Evidence is provided suggesting that AP-1 binding is associated with an increase in IL-1 alpha expression, an early mediator of toxic response in the skin.

Acetaminophen-induced hepatotoxicity is associated with early changes in AP-1 DNA binding activity

The AP-1 transcription factor family, which is involved in early response genes, consists of two groups of proteins, Fos-related antigens (fra) and Jun proteins. AP-1 is usually expressed at low basal cellular levels, but can be up-regulated by a variety of exogenous stimuli which results in synthesis of Fos and Jun proteins and increased AP-1 DNA binding activity. Changes in early immediate gene responses are associated with liver necrosis, inflammation and repair, although investigations into their role in drug-induced hepatotoxicity have not been actively examined. In the present studies, we determined that exposure to necrogenic doses of acetaminophen (APAP) was associated with increased AP-1 DNA binding activity in mouse liver. The APAP-induced hepatic AP-1 DNA binding complex had affinity for both the consensus AP-1 and CRE sequences. Furthermore, c-jun, but not c-fos, mRNA transcripts were transiently increased following exposure to hepatotoxic doses of APAP. When endotoxin was administered to mice in order to elicit a hepatic inflammatory response without necrosis, increases in c-jun expression occurred without accompanying changes in AP-1 activity, indicating a different mechanism of action. When compared to conventional indicators of hepatotoxicity, such as plasma levels of liver-associated enzymes, changes in gene expression occurred much earlier and, at least with AP-1 activity, remained activated following normalization of liver enzyme levels. These studies suggest that the AP-1 transcription factor and associated genes are associated in the hepatotoxic response of liver to APAP and may serve as useful molecular biomarkers for chemical-induced hepatotoxicity.

Histopathology of acetaminophen-induced liver changes: role of interleukin 1 alpha and tumor necrosis factor alpha

Administration of 500 mg/kg acetaminophen (APAP) to female B6C3F1 mice resulted in well-documented pathophysiological changes in the liver manifested as increased serum concentration of liver enzymes (aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, and serum sorbitol dehydrogenase), centrilobular congestion, and hepatocellular degeneration and necrosis. The role of proinflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha) and interleukin 1 alpha (IL-1 alpha), on the hepatotoxicity of APAP was examined at 4, 8, 12, and 24 hr following APAP administration. Neutralization of TNF-alpha or IL-1 alpha with specific antibodies partially prevented the hepatotoxic effects of APAP at the 4- and 8-hr time points. In addition, prior administration of anti-TNF-alpha antibodies shortened the recovery time following APAP treatment. While IL-1 receptor antagonist (IL-1ra) had only a modest protective effect against APAP-induced liver damage, as determined by serum enzyme release, IL-1ra had no effect on the degree of hepatic congestion or necrosis at any of the time points examined. On the other hand, administration of antibodies against IL-1ra exacerbated APAP-induced liver toxicity. These results suggest that TNF-alpha and IL-1 alpha play an important role in the degree of damage and recovery that the liver undergoes following APAP intoxication.

Induction of CYP1A1 and ALDH-3 in lymphoid tissues from Fisher 344 rats exposed to 2,3,7,8-tetrachlorodibenzodioxin (TCDD)

The immune system is a primary target for toxic insult by a number of drugs and environmental chemicals, many of which require activation to toxic metabolites by drug-metabolizing enzymes. We compared the induction of drug-metabolizing enzymes, including cytochrome P450 1A1 (CYP1A1) and aldehyde dehydrogenase (ALDH), in lymphoid tissues of F344 rats following treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). ALDH was induced in both the spleen and the thymus after TCDD treatment, with maximal expression at 9 and 15 days, respectively. Thymic microsomal preparations from TCDD-treated animals expressed elevated levels of inducible CYP1A1 as compared to microsomes from the spleens of treated animals or tissues from control rats. TCDD treatment also resulted in increased ethoxyresorufin-O-deethylase (EROD) activity in the thymus. There were no detectable mRNA transcripts for CYP1A1 in peripheral blood or splenic lymphocytes from treated animals; however, CYP1A1 transcripts were induced in isolated thymocytes, whole spleen, and whole thymus. In vitro exposure to TCDD did not result in induction of immunoreactive CYP1A1 in thymocytes unless simultaneously activated with the mitogen, phytohemagglutinin (PHA). Immunohistochemical localization of CYP1A1 in immune tissues indicated that cells other than the lymphoid populations are responsible for the increased CYP1A1 expression. The pattern of CYP1A1 induction was related to the expression of the Ah receptor (AhR) in immune tissues. Western blot analyses demonstrated less AhR present in peripheral blood lymphoid cells and spleen, as compared to whole tissues. These studies indicate that while drug-metabolizing enzymes are present in immune tissues, the induction of enzymes is selective in different lymphoid cells.

Role of keratinocyte-derived cytokines in chemical toxicity

Following appropriate stimulation, such as with tumor promoters, ultraviolet light or various chemical agents, keratinocytes synthesize and secrete cytokines which can mediate or participate in dermatotoxic responses such as inflammation, hyperkeratosis, hypersensitivity and skin cancer. We have determined the qualitative and quantitative cytokine response in primary human keratinocyte cultures following exposure to several non-sensitizing contact irritants, sensitizers and ulcerative agents as well as a skin carcinogen. The chemicals were also administered to mice to assess whether the dermatotoxic response correlated with the in vitro production of keratinocyte-derived cytokines. Due to the complex cellular interactions that occur in the skin, it was not possible to identify specific cytokine profiles for most of the classes of dermatotoxic agents studied. However, the non-sensitizing contact irritants produced relative increases in the synthesis and secretion of the proinflammatory cytokines, interleukin-1 and tumor necrosis factor-alpha, as well as the neutrophil chemotactic cytokine, interleukin-8 compared to the other chemical agents. While ulcerative compounds as well as irritants elicited neutrophils to the site of chemical application when applied to the mouse skin, time-dependent and chemical-specific patterns of inflammation were detected. Treatment of human keratinocyte cultures with arsenic, a human skin carcinogen, resulted in a unique cytokine profile characterized by induction of growth factors, including transforming growth factor-alpha and granulocyte-macrophage colony stimulating factor. Treatment of v-Ha-ras transgenic mice, an animal model for skin cancer, with arsenic caused an increase in the number of papillomas as well as overexpression of these growth factors suggesting that they participate in arsenic-induced skin papilloma development. These studies indicate a diverse role exists for keratinocyte-derived cytokines in dermatotoxic actions.

Tumor necrosis factor-alpha and nitric oxide production in endotoxin-primed rats administered carbon tetrachloride

Tumor necrosis factor-alpha (TNF alpha) is elevated in the sera of rats administered non-lethal doses of carbon tetrachloride (CCl4) followed by endotoxin. Elevated TNF alpha levels are correlated with the increased release of hepatic enzymes indicating hepatic damage. Under these conditions, nitric oxide (NO) was also produced in the liver as evidenced by the formation of nitrosyl complexes which were measured by electron paramagnetic resonance (EPR) spectroscopy. Decreased nitrosyl complex formation occurred in livers following treatment with either an inhibitor or macrophage activation (gadolinium trichloride; GdCl3), an inhibitor of cytokine responses (dexamethasone) or a NO synthase inhibitor (NG-monomethyl-L-arginine; 1-NMA), GdCl3 or dexamethasone treatment decreased, while 1-NMA treatment increased, TNF alpha serum level. Taken together, these data suggest that TNF alpha and NO are induced following CCl4 and LPS exposure and may be important regulators in the hepatotoxicity of this liver injury model.

Comparative assessment of metabolic enzyme levels in macrophage populations of the F344 rat

The immune system is a direct target for toxic insult by a number of drugs and other chemicals, many of which require activation to toxic metabolites by drug-metabolizing enzymes. We compared the induction of drug-metabolizing enzymes, including cytochrome P450 1A1 (CYP1A1) and aldehyde dehydrogenase (ALDH), which are differentially expressed in various macrophage populations following treatment of F344 rats with the inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Kupffer cells, alveolar macrophages and splenic macrophages from TCDD-treated animals expressed elevated levels of inducible CYP1A1 as compared to other macrophage subpopulations or cells from control rats. TCDD treatment also resulted in increased ethoxyresorufin-O-deethylase (EROD) activity and total cytochrome P450 content in tissue-derived macrophages. Immunoreactive protein and mRNA transcripts for CYP1A1 were not detectable in resident peritoneal macrophages or peripheral blood monocytes. Examination of aromatic hydrocarbon receptor (AhR) levels in macrophage populations suggests that the ability of TCDD to induce metabolic enzymes in specific cell types correlates well with AhR expression. In vivo activation of macrophages, using either Bacillus of Calmette and Guérin, Mycobacterium tuberculosis (BCG) or polyinosinic:polycytidylic acid (Poly I:C), caused no significant alteration in the levels of induction of CYP1A1. ALDH-3 induction was similar in all macrophage populations examined. These studies indicate that macrophages, particularly those from portals of entry, may be induced to produce increased levels of specific enzymes, and the induction is dependent upon their maturational stage rather than their activation state. The metabolism of xenobiotics to toxic intermediates by immune cells and its role in immunosuppression are discussed.

Local versus systemic immunotoxicity of isobutyl nitrite following subchronic inhalation exposure of female B6C3F1 mice

Female B6C3F1 mice were exposed to isobutyl nitrite (IBN) by inhalation at 0, 37.5, 75, or 150 ppm for 6 hr per day, 5 days per week for 15 weeks. The potential of this compound to induce immunotoxicity was assessed during the 3rd, 13th, 14th, and 15th week of exposure and after 2 weeks of recovery following the 15 weeks of exposure. Both systemic and lung immune functions were examined, including body and lymphoid organs weights, pulmonary macrophage function and host defense, expression of splenic lymphocyte cell-surface markers, natural killer cell function, mixed lymphocyte reaction, and induction of specific antibody to a T-cell-dependent antigen. There was a dose-related suppression of T-cell-dependent antibody-forming cell responses in the spleen following IBN exposure; however, other measures of T-cell and nonspecific immunity were not significantly affected. A dose-related increase of H202 production by alveolar macrophages was present after 12 but not after 68 exposures to IBN. In contrast, pulmonary host defense mechanisms against Klebsiella pneumoniae were unaffected. These results suggest that in the absence of changes in host resistance, IBN may have selective and partially reversible effects on the immune system.

Cadmium-induced renal damage and proinflammatory cytokines: possible role of IL-6 in tubular epithelial cell regeneration

Cadmium exposure in humans and experimental animals produces renal damage characterized by degeneration and necrosis of tubular epithelial cells followed by interstitial inflammation and eventual regeneration of proximal tubular cells. Since chronic kidney diseases are often associated with the presence of inflammatory cytokines and cadmium has been reported to alter cytokine expression in monocytes and the Kupffer cells of the liver, we investigated the role of proinflammatory cytokines in cadmium-induced nephrotoxicity. Increases in TNF-alpha and IL-6 cytokine mRNA transcripts and secretion were observed in the kidney following exposure of LPS-primed mice to a total of 21 mg/kg body weight cadmium administered over a 14-week period. IL-6 was the predominant cytokine expressed and was found to be present in mesangial cells. Cadmium, in the presence of LPS, was able to induce IL-6 secretion in vitro from mouse glomerular mesangial cells. Proliferative cell nuclear antigen (PCNA) staining revealed increases in regeneration of tubular epithelial cells following cadmium exposure. Furthermore, renal tubular epithelial cells responded to IL-6 by marked proliferation. Taken together, these data suggest that cadmium-induced IL-6 secretion in the kidney may act to support the regeneration of renal tubular epithelial cells that occurs in the course of cadmium nephrotoxicity.