Etanercept attenuates immune-mediated hepatitis induced by concanavalin A via differential regulation of the key effector cytokines of CD4+ T cells

AIMS

The current study aims to investigate the role of the key effector cytokines produced by CD4+T cells in the pathogenesis of Con A-induced liver injury in mice and testing whether etanercept can be repurposed to differentially regulate these cytokines.

MAIN METHODS

Four groups of mice were used: group I: control group, group II: mice received 15 mg/kg Con A i.v, group III: mice received 15 mg/kg etanercept i.p, group IV: mice received both Con A and etanercept as described. Hepatic injury and necroinflammation were assessed. Infiltration of CD4+ T cells and neutrophils were evaluated. Hepatic levels of TNF-α, IL-4, IL-10, and MDA were assigned and expression of NF-κB as well.

KEY FINDINGS

A significant decrease in ALT, AST, and LDH levels occurred when etanercept was injected before Con A. Hepatic necrosis and infiltration of CD4+ T cells and neutrophils were reduced by etanercept. Levels of TNF-α, IL-4, and MDA were significantly decreased in group IV compared to group II while that of IL-10 was increased. Also, number of NF-κB positive cells was significantly low in group IV.

SIGNIFICANCE

The study elucidates an interplay between the two effector cytokines of CD4+ T cells, TNF-α and IL-4, and their key role in Con A-induced liver injury. Additionally, our results showed that etanercept could be repurposed to differentially regulate effector cytokines produced by CD4+ T cells. Not only TNF-α, but also IL-4 signaling pathways, through which it exerts immunomodulatory, anti-inflammatory, and anti-oxidant effects leading to attenuation of Con A-induced liver injury.

Differential modulation of immune response and cytokine profiles of Sargassum horneri ethanol extract in murine spleen with or without Concanavalin A stimulation

The health benefit of brown seaweeds has been proclaimed for centuries, particularly in Asian countries. A brown seaweed Sargassum horneri has been suggested to have immune-boosting and anti-inflammatory/immune-regulatory effects, but their mechanism is still elusive. This study researches the immunological effect of 70% ethanol extract of S. horneri (SHE) on unstimulated and Con A-stimulated murine splenocytes. When treated alone, SHE had an immune stimulatory effect on CD3e+ CD4+ T-helper cells, CD3e+ CD8+ cytotoxic T cells, CD45+ CD11b+ macrophages, Ly-6C+ Ly-6 G+ granulocytes, and Ly6 G- Ly6Clow eosinophils. Furthermore, SHE enhanced wide spectrum of Th cytokines such as TNF-α, IFN-γ (Th1), IL-4, IL-5, IL-13 (Th2), and IL-6 (Th17), which also stimulated the macrophage polarizing cytokines and enhanced macrophage derived cytokine secretion. SHE in Con A (5 μg/mL) stimulated cells decreased T-helper, cytotoxic T cells, granulocytes, eosinophils, and monocytes. These results signify the potential immuno-modulatory effect of SHE which can be developed as a therapeutic agent in immuno-compromised individuals.

The protective role of myeloid-derived suppressor cells in concanavalin A-induced hepatic injury

The mechanism underlying T cell-mediated fulminant hepatitis is not fully understood. In this study, we investigated whether myeloid derived suppressor cells (MDSCs) could prevent the concanavalin A (ConA)-induced hepatitis through suppressing T cell proliferation. We observed an increase in the frequencies of MDSCs in mouse spleen and liver at early stage of ConA treatment, implicating that the MDSCs might be involved in the initial resistance of mice against ConA-mediated inflammation. Subpopulation analysis showed that the MDSCs in liver of ConA-induced mice were mainly granulocytic MDSCs. Adoptive transfer of the bone marrow-derived MDSCs into ConA-treated mice showed that the MDSCs migrated into the liver and spleen where they suppressed T cell proliferation through ROS pathway. In addition, the frequencies of MDSCs in mice were also significantly increased by the treatment with immune suppressor glucocorticoids. Transfer of MDSCs into the regulatory T cell (Treg)-depleted mice showed that the protective effect of MDSCs on ConA-induced hepatitis is Treg-independent. In conclusion, our results demonstrate that MDSCs possess a direct protective role in T cell-mediated hepatitis, and increasing the frequency of MDSCs by either adoptive transfer or glucocorticoid treatment represents a potential cell-based therapeutic strategy for the acute inflammatory disease.

Ethyl pyruvate pretreatment attenuates concanavalin a-induced autoimmune hepatitis in mice

Pharmacological Relevance

Ethyl pyruvate (EP), a potent reactive oxygen species scavenger, has been reported to contribute to the inflammatory process. However, the protective effect of ethyl pyruvate on Concanavalin A (Con A)-induced autoimmune hepatitis have not been explored. Thus, the aims of this study are to investigate both the effects of ethyl pyruvate and its mechanism of protection on Con A-induced autoimmune hepatitis in mice.

Materials and Methods

Acute autoimmune hepatitis was induced by Con A (20 mg/kg) in Balb/C mice; ethyl pyruvate (40 mg/kg and 80 mg/kg) was administrated 1h prior to the Con A injection. At 3h, 6h and 24h post Con A injection, histological grading, proinflammatory cytokine levels and nuclear factor kappa B (NF-κB) activity were determined.

Results

Following Con A challenge, cytokines TNF-α, IL-2, IL-1β and IL-6 were expressed at 3h and 6h, and the level of HMGB1 significantly increased by 24h. Pretreatment with ethyl pyruvate ameliorated the pathological effects of Con A-induced autoimmune hepatitis and significantly decreased the levels of TNF-α, IL-2, IL-6 and IL-1β at 3h and 6h and the level of HMGB1 at 6h and 24h post injection. Ethyl pyruvate blocked the degradation of IκB α and IκB β and decreased the expression of NF-κB at 24h.

Conclusion

Taken together, these results indicated that ethyl pyruvate protected against Con A-induced autoimmune hepatitis by decreasing both early (TNF-α, IL-2, IL-1β and IL-6) and late (HMGB1) cytokine expression in mice. The reduction of HMGB1 may correlate with the amelioration of NF-κB activity.

Mechanism of entomotoxicity of the Concanavalin A in Rhopalosiphum padi (Hemiptera: Aphididae)

The toxicity effect of Concanavalin A (Canavalia ensiformis lectin, ConA) to bird cherry-oat aphid, Rhopalosiphum padi L. (Hemiptera: Aphididae), was investigated in the laboratory by using artificial diets containing ConA concentrations. Bird cherry-oat aphid performance was affected by the presence of Con A in artificial diets. The lectin added into the liquid diet increased the prereproductive period, mortality, and the average time of generation development (T) and decreased fecundity and the intrinsic rate of natural increase (rm). In attempt to unravel the mode of action of ConA, the interaction of the lectin with insect gut and the effect of ConA on feeding behavior were investigated. Extract of gut of treated grain aphid demonstrated DNA fragmentation, and this was accompanied with an increase in caspase 3 activity. Moreover, addition of ConA to the sucrose-agarose gels reduced salivation and passive ingestion of fluids from the gel. The results indicate that the insecticidal activity of ConA on R. padi may involve effects on death of the gut epithelial cells and effects on feeding behavior. This can be employed to create plants that are resistant to aphids.

Inhibition of natural killer cells protects the liver against acute injury in the absence of glycine N-methyltransferase

Glycine N-methyltransferase (GNMT) catabolizes S-adenosylmethionine (SAMe), the main methyl donor of the body. Patients with cirrhosis show attenuated GNMT expression, which is absent in hepatocellular carcinoma (HCC) samples. GNMT(-/-) mice develop spontaneous steatosis that progresses to steatohepatitis, cirrhosis, and HCC. The liver is highly enriched with innate immune cells and plays a key role in the body's host defense and in the regulation of inflammation. Chronic inflammation is the major hallmark of nonalcoholic steatohepatitis (NASH) progression. The aim of our study was to uncover the molecular mechanisms leading to liver chronic inflammation in the absence of GNMT, focusing on the implication of natural killer (NK) / natural killer T (NKT) cells. We found increased expression of T helper (Th)1- over Th2-related cytokines, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-R2/DR5, and several ligands of NK cells in GNMT(-/-) livers. Interestingly, NK cells from GNMT(-/-) mice were spontaneously activated, expressed more TRAIL, and had strong cytotoxic activity, suggesting their contribution to the proinflammatory environment in the liver. Accordingly, NK cells mediated hypersensitivity to concanavalin A (ConA)-mediated hepatitis in GNMT(-/-) mice. Moreover, GNMT(-/-) mice were hypersensitive to endotoxin-mediated liver injury. NK cell depletion and adoptive transfer of TRAIL(-/-) liver-NK cells protected the liver against lipopolysaccharide (LPS) liver damage.

CONCLUSION

Our data allow us to conclude that TRAIL-producing NK cells actively contribute to promote a proinflammatory environment at early stages of fatty liver disease, suggesting that this cell compartment may contribute to the progression of NASH.

Mitogenic potency of insulin glargine

The goal of diabetes mellitus treatment is to maintain long-term near-normoglycaemia to prevent the onset or progression of long-term complications. In order to achieve tight glycaemic control and improve the quality of life for diabetic patients, a number of novel insulin preparations, insulin analogues, have been constructed thanks to recombinant DNA technologies and advanced protein chemistry. Because structurally modified insulins may differ from human insulin not only in metabolic but also in mitogenic potencies there were concerns raised about the possibility of increased insulin analogue proliferative action or tumourigenesis. In vitro and in vivo studies on insulin analogues in comparison to endogenous insulin have been performed to closely monitor the insulin analogue action profiles. Insulin glargine was the only one presenting a significant increase in affinity to insulin-like growth factor type 1 (IGF-1) receptor. However, there was controversy regarding the safety of insulin glargine use because of its potential risk of mitogenicity but it proved to be true only for human osteosarcoma cells Saos/B10. Outcomes of the studies performed on lines other than cancer cells and on animals did not present any increased mitogenic activity nor mitogenic potency of insulin glargine in comparison to human insulin.

Increased circulating pro-inflammatory cytokines and imbalanced regulatory T-cell cytokines production in chronic idiopathic urticaria

The immunologic characterization of chronic idiopathic urticaria (CIU), mainly regarding cytokine profile needs more investigation. We examined circulating inflammatory cytokine levels, T-cell induced secretion, and cytokine mRNA expression in patients with CIU subjected to the intradermal autologous serum skin test (ASST). Increased levels of circulating pro-inflammatory cytokines, such as TNF-alpha, IL-1beta, IL-12p70, and IL-6 have been observed in most of patients with CIU, together with an enhancement of IL-2 secretion following T-cell stimulation. Highlighting the inflammatory profile in CIU found in ASST positive, is the enhanced B-cell proliferative responsiveness and increased IL-17 secretion levels. ASST-positive patients also exhibited impaired IL-4 secretion associated with increased IL-10 production. Altered cytokine expression in patients with ASST-negative, was the down-modulation of spontaneous IL-10 mRNA expression levels in peripheral blood mononuclear cells. Our findings support the concept of immunologic dysregulation in CIU, revealing a systemic inflammatory profile associated with disturbed cytokine production by T cells, mainly related to IL-17 and IL-10 production.

Inhalation of tobacco smoke induces increased proliferation of urinary bladder epithelium and endothelium in female C57BL/6 mice

Cigarette smoking is the major environmental risk factor for bladder cancer in humans. Aromatic amines, potent DNA-reactive bladder carcinogens present in cigarette smoke, contribute significantly. However, increased cell proliferation, caused by direct mitogenesis or in response to cytotoxicity, may also play a role since urothelial hyperplasia has been observed in human cigarette smokers. We examined the urothelial effects of cigarette smoke (whole body inhalation exposure (Teague) system) in female C57BL/6 mice at various times in two studies, including reversibility evaluations. In both studies, no urothelial hyperplasia was observed by light microscopy in any group. However, in study 1, the Ki-67 labeling index (LI) of the urothelium was significantly increased in the smoke exposed group compared to controls through 3 months, but was not present at 6, 9 or 12 months even with continued exposures. In the groups that discontinued smoke exposure, it returned to the same levels as controls or lower. In study 2, the bromodeoxyuridine LI was similar to controls on day 1 but significantly increased at 5 days in the smoke exposed group. In the group that discontinued smoke exposure for 2 days, the LI was increased compared to controls but not significantly. Superficial urothelial cell cytotoxicity and necrosis were detectable by scanning electron microscopy at 5 days. Changes in LI of submucosal endothelial cells generally followed those of the urothelium and effects were reversible upon cessation of exposure. The increased urothelial proliferation appeared to be due to superficial cell cytotoxicity with consequent regeneration.

A mode of action for induction of liver tumors by Pyrethrins in the rat

High doses of Pyrethrins produce liver tumors in female rats. To elucidate the mode of action for tumor formation, the hepatic effects of Pyrethrins have been investigated. Male Sprague-Dawley CD rats were fed diets containing 0 (control) and 8000 ppm Pyrethrins and female rats' diets containing 0, 100, 3000 and 8000 ppm Pyrethrins for periods of 7, 14 and 42 days and 42 days followed by 42 days of reversal. As a positive control, rats were also fed diets containing 1200-1558 ppm sodium Phenobarbital (NaPB) for 7 and 14 days. The treatment of male rats with 8000 ppm Pyrethrins, female rats with 3000 and 8000 ppm Pyrethrins and both sexes with NaPB resulted in increased liver weights, which were associated with hepatocyte hypertrophy. Hepatocyte replicative DNA synthesis was also increased by treatment with Pyrethrins and NaPB. The treatment of male and female rats with Pyrethrins and NaPB produced significant increases in hepatic microsomal cytochrome P450 (CYP) content and a marked induction of CYP2B-dependent 7-pentoxyresorufin O-depentylase and testosterone 16beta-hydroxylase activities. Significant increases were also observed in CYP3A-dependent testosterone 6beta-hydroxylase activity. The hepatic effects of Pyrethrins were dose-dependent in female rats with 100 ppm being a no effect level and on cessation of treatment were reversible in both sexes. This study demonstrates that Pyrethrins are mitogenic CYP2B form inducers in rat liver. The mode of action for Pyrethrins-induced rat liver tumor formation appears to be similar to that of NaPB and some other non-genotoxic CYP2B inducers of hepatic xenobiotic metabolism.

Nicotine as a mitogenic stimulus for pancreatic acinar cell proliferation

Cell proliferation is an important process in life for growth of normal and cancer cells. The signal transduction pathways activated during this process are strictly regulated. This editorial focuses on the role of nicotine, a mitogen, in the induction of signaling pathways resulting in proliferation of pancreatic tumor cells and compares these events with those in normal acinar cells isolated from the rat pancreas. The data shows striking similarities between these two cellular systems. In addition, the editorial reviews very recent literature of the contribution of MAPK signaling in cell lines associated with human diseases. A prospective cellular model of nicotine induced activation of MAPK cascade is presented.

Mitogenic signal transduction caused by monomethylarsonous acid in human bladder cells: role in arsenic-induced carcinogenesis

Previous studies have shown that human bladder cells (UROtsa), a target of arsenic-induced cancer, can biotransform arsenite to monomethylarsonous acid (MMA(III)), which is more cytotoxic and capable of transforming the UROtsa cells following long-term, low-level exposure. Cyclooxygenase-2 (COX-2) causes hyperplasia in bladder cells and is considered a key biomarker in bladder cancer. To investigate the role of mitogenic pathway stimulation in MMA(III)-induced transformation, UROtsa cells were treated with 50nM MMA(III) for 12, 24, or 52 weeks and analyzed by Western blot for COX-2 expression. Elevations in COX-2 expression were noted following chronic MMA(III) exposure, and this induction increased with duration of exposure, suggesting that COX-2 or the signal transduction pathways responsible for COX-2 protein expression may play a role in MMA(III)-induced transformation. Acute exposure studies found MMA(III) treatment (10, 50, and 100nM, 4 h) induced COX-2 in UROtsa cells with the lowest doses (10 and 50nM) causing the strongest induction. Using pharmacological inhibitors of various pathways, it was shown that epidermal growth factor receptor (EGFR), extracellular signal-regulated kinase (ERK-1/-2), phosphoinositide 3-kinase (PI3K), and src were important in the induction of COX-2 by MMA(III). ERK-2 phosphorylation was verified by Western blot analysis with a peak at 15 min, and c-jun was translocated to the nucleus following 50nM MMA(III) treatment. To determine MMA(III) targets, receptors of the erythroblastosis oncogene family (ErbB) family were further investigated. Chronic MMA(III) exposure led to upregulation of the EGFR or ErbB1. Short-term MMA(III) treatment caused the phosphorylation of ErbB2 in its autophosphorylation site. To verify the importance of these signaling pathways to the growth of the MMA(III)-transformed UROtsa cells in soft agar, various inhibitors were used to block pathways and monitor cells growth. Pathways of importance in anchorage-independent growth of UROtsa cells chronically exposed to MMA(III) are src, PI3K, and COX-1 and -2. As COX-2 is an important mediator that contributes to carcinogenesis via promotion of cell proliferation, inhibition of cell death, induction of angiogenesis, and facilitation of invasion, and it is highly upregulated both acutely and chronically in the MMA(III)-transformed cells, it is likely that activation of the mitogen-activated protein kinase pathway and increased COX-2 expression is a plausible mechanism for MMA(III) bladder carcinogenesis.

Lead-induced genotoxicity in lymphocytes from peripheral blood samples of humans: in vitro studies

Lead is a known toxicant that has been implicated in encephalopathy in children and may affect the gastrointestinal and hematopoietic and other systems in adults. In fact, lead has been shown to compete with calcium for entry into the synaptosome and induce toxic effects. The aim of the current study was to evaluate the cytotoxic and genotoxic effects of lead by using lymphocytes from human peripheral blood in vitro. The LC50 for lead nitrate as determined by Trypan blue dye exclusion technique was found to be 3.14 mM. Chromosomal aberration frequency at sublethal doses (1/10 of LC50) as determined by examining the metaphase chromosomes (karyotyping) did not show significant aberrations except for some aneuploidy and about 2-4% gaps, breaks (3-4%), and about 5% satellite associations. However, significant DNA damage was determined by SCGE (Comet assay). The comet tail length proportionately increased with increasing lead nitrate concentration. Thus, Pb can induce single-strand DNA breaks, possibly by competing with metal binding sites.

The use of micronucleus test for detection of genotoxic damage to the thyroid gland

We studied the possibility of using the micronucleus test in in vivo experiments on the model of rat follicular thyrocytes prestimulated to cell division (hemithyroidectomy). Single administration of N-nitroso-N-methylurea produced a significant dose-dependent effect on micronucleus formation in thyrocytes and polychromatophilic erythrocytes of the bone marrow. The test system allowed us to reveal a cumulative effect of 2-fold and 4-fold treatment with the mitogen in low or subthreshold doses on the thyroid gland. Our results indicate that the micronucleus test is an informative method for the analysis of the effect of genotoxic agents on the thyroid parenchyma.

Mitogenic estrogen metabolites alter the expression of 17beta-estradiol-regulated proteins including heat shock proteins in human MCF-7 breast cancer cells

Estrogen metabolites are carcinogenic. The comparative mitogenic activities of 17b-estradiol (E2) and four metabolites, 2-hydroxyestradiol (2-OHE2), 4-hydroxyestradiol (4-OHE2), 16a-hydroxyestrone (16a-OHE1) and 2-methoxyestradiol (2-ME), were determined in estrogen receptor(ER)-positive MCF-7 human breast cancer cells. Each of the E2 metabolites caused proliferation of the MCF-7 cells, but only E2 and 16a-OHE1 induced a greater than 20-fold increases in transcripts of the progesterone receptor (PR) gene, a classical ER-mediated gene. This suggests that the mitogenic action of E2 and 16a-OHE1 could result from their effects on gene expression via the ER. E2 metabolites altered the expression of E2-regulated proteins including heat shock proteins (Hsps). 16a-OHE1 and 2-ME as well as E2 increased levels of Hsp56, Hsp60, Hsp90a and Hsp110 transcripts, and the patterns of these inductions resembled that of PR. Hsp56 and Hsp60 protein levels were increased by all the E2 metabolites. Levels of the transcripts of 3 E2-upregulated proteins (XTP3-transactivated protein A, protein disulfide isomerase-associated 4 protein and stathmin 1) and an E2-downregulated protein (aminoacylase 1) were also affected by the E2 metabolites. These results suggest that the altered expression of Hsps (especially Hsp56 and Hsp60) by E2 metabolites such as E2, 16a-OHE1 and 2-ME could be closely linked to their mitogenic action.

Leukotoxin diols from ground corncob bedding disrupt estrous cyclicity in rats and stimulate MCF-7 breast cancer cell proliferation

Previous studies in our laboratory demonstrated that high-performance liquid chromatography (HPLC) analysis of ground corncob bedding extracts characterized two components (peak I and peak II) that disrupted endocrine function in male and female rats and stimulated breast and prostate cancer cell proliferation in vitro and in vivo. The active substances in peak I were identified as an isomeric mixture of 9,12-oxy-10,13-dihydroxyoctadecanoic acid and 10,13-oxy-9,12-dihydroxyoctadecanoic acid, collectively designated tetrahydrofurandiols (THF-diols). Studies presented here describe the purification and identification of the HPLC peak II component as 9,10-dihydroxy-12-octadecenoic acid (leukotoxin diol; LTX-diol), a well-known leukotoxin. A synthetic mixture of LTX-diol and 12,13-dihydroxy-9-octadecenoic acid (iso-leukotoxin diol; i-LTX-diol) isomers was separated by HPLC, and each isomer stimulated (p < 0.001) MCF-7 cell proliferation in an equivalent fashion. The LTX-diol isomers failed to compete for [3H]estradiol binding to the estrogen receptor or nuclear type II sites, even though oral administration of very low doses of these compounds (>> 0.8 mg/kg body weight/day) disrupted estrous cyclicity in female rats. The LTX-diols did not disrupt male sexual behavior, suggesting that sex differences exist in response to these endocrine-disruptive agents.

Lack of direct mitogenic activity of dichloroacetate and trichloroacetate in cultured rat hepatocytes

Dichloroacetate (DCA) and trichloroacetate (TCA) are hepatocarcinogenic metabolites of the common groundwater contaminant, 1,1,2-trichloroethylene. DCA and TCA have been shown to induce hepatocyte proliferation in vivo, but it is not known if this response is the result of direct mitogenic activity or whether cell replication occurs indirectly in response to tissue injury or inflammation. In this study we used primary cultures of rat hepatocytes, a species susceptible to DCA- but not TCA-induced hepatocarcinogenesis, to determine whether DCA and TCA are direct hepatocyte mitogens. Rat hepatocytes, cultured in growth factor-free medium, were treated with 0.01-1.0 mM DCA or TCA for 10-40 h; cell replication was then assessed by measuring incorporation of 3H-thymidine into DNA and by cell counts. DCA or TCA treatment did not alter 3H-thymidine incorporation in the cultured hepatocytes. Although an increase in cell number was not observed, DCA treatment significantly abrogated the normal background cell loss, suggesting an ability to inhibit apoptotic cell death in primary hepatocyte cultures. Furthermore, treatment with DCA synergistically enhanced the mitogenic response to epidermal growth factor. The data indicate that DCA and TCA are not direct mitogens in hepatocyte cultures, which is of interest in view of their ability to stimulate hepatocyte replication in vivo. Nevertheless, the synergistic enhancement of epidermal growth factor-induced hepatocyte replication by DCA is of particular interest and warrants further study.

Pentachlorophenol-Induced Cytotoxic, Mitogenic, and Endocrine-Disrupting Activities in Channel Catfish, Ictalurus punctatus

Pentachlorophenol (PCP) is an organochlorine compound that has been widely used as a biocide in several industrial, agricultural, and domestic applications. Although it has been shown to induce systemic toxicity and carcinogenesis in several experimental studies, the literature is scarce regarding its toxic mechanisms of action at the cellular and molecular levels. Recent investigations in our laboratory have shown that PCP induces cytotoxicity and transcriptionally activates stress genes in human liver carcinoma (HepG2) cells [1]. In this research, we hypothesize that environmental exposure to PCP may trigger cytotoxic, mitogenic, and endocrine-disrupting activities in aquatic organisms including fish. To test this hypothesis, we carried out in vitro cultures of male channel catfish hepatocytes, and performed the fluorescein diacetate assay (FDA) to assess for cell viability, and the Western Blot analysis to assess for vitellogenin expression following exposure to PCP. Data obtained from FDA experiments indicated a strong dose-response relationship with respect to PCP cytotoxicity. Upon 48 hrs of exposure, the chemical dose required to cause 50% reduction in cell viability (LD50) was computed to be 1,987.0 +/- 9.6 microg PCP/mL. The NOAEL and LOAEL were 62.5 +/- 10.3 microg PCP/mL and 125.0+/-15.2 microg PCP/mL, respectively. At lower levels of exposure, PCP was found to be mitogenic, showing a strong dose- and time-dependent response with regard to cell proliferation. Western Blot analysis demonstrated the potential of PCP to cause endocrine-disrupting activity, as evidenced by the up regulation of the 125-kDa vitellogenin protein the hepatocytes of male channel catfish.

Mitogenic and Cytotoxic Effects of Pentachlorophenol to AML 12 Mouse Hepatocytes

Pentachlorophenol (PCP), an organochlorine fungicide, is extensively used in the United States for the protection of wood products. Moreover, widespread agricultural, domestic, and industrial applications have caused PCP-contaminants to enter the food chain from the environment. There is accumulating evidence indicating that PCP is highly toxic to humans, and causes injury to major organs including the lung, liver, kidneys, heart, and brain. While PCP has been shown to induce systemic toxicity and carcinogenesis in several experimental studies, the literature is scarce regarding its toxic mechanisms of action. Recent investigations in our laboratory have shown that PCP exerts both cytotoxic and mitogenic effects in human liver carcinoma (HepG2) cells [1], and in primary culture of catfish hepatocytes [2]. In the present study, we hypothesized that PCP exposure will trigger similar cytotoxic and mitogenic responses in AML 12 Mouse hepatocytes. To test this hypothesis, we performed the MTT assay for cell viability in PCP-treated and control cells. Data obtained from this experiment indicated a biphasic response with respect to PCP toxicity; showing a hormosis effect characterized by mitogenicity at lower levels of exposure, and cytotoxicity at higher doses. Upon 48 hrs of exposure, PCP chemical doses required to cause 50% reduction in the viability (LC50) of AML 12 mouse hepatocytes was computed to be 16.0 + 2.0 microg/mL. These results indicate that, although the sensitivity to PCP toxicity varies from one cell line to another, its toxic mechanisms are similar across cell lines.

Possible mechanisms underlying the mitogenic actionof heptachlor in rat hepatocytes

The worldwide use of the organochlorine pesticide heptachlor has led to widespread contamination in the environment. Like many other organochlorine pesticides, heptachlor is considered to pose a threat to human health. It has been shown that heptachlor is a tumor-promoting agent, but the mechanisms involved still remain unclear. The negative response of heptachlor in in vitro genotoxicity test suggests that this pesticide displays its carcinogenicity through epigenetic pathways. With the growing evidence that proliferation accounts for the tumor-promoting effects of many agents, the purpose of this work was to investigate the mechanisms involved in the mitogenic activity of heptachlor in quiescent rat hepatocytes and to understand the properties of this compound as a tumor promoter in the liver. Heptachlor triggered significant proliferation in quiescent rat hepatocytes. Two mechanisms were delineated to support the mitogenic effect in the hepatocyte: activation of key kinases in signaling pathways and inhibition of apoptosis. Exposure to heptachlor led to activation of protein kinase C mitogenactivated protein kinases. Moreover, these results indicate that like many tumor promoters, heptachlor strongly inhibited TGFbeta-induced apoptosis and cytochrome c release into the cytosol. The levels of the anti-apoptotic protein Bcl-2 were also increased in the presence of heptachlor. In conclusion, these results indicate that heptachlor alters basic cell function by interfering with key cellular signaling pathways.

Trocarin, a blood coagulation factor Xa homologue from snake venom, causes inflammation and mitogenesis

Trocarin, a Group D prothrombin activator from Tropidechis carinatus snake venom, has high sequence similarity to blood coagulation factor Xa (FXa). Both trocarin and FXa activate prothrombin to mature thrombin and have similar requirements for cofactors, such as factor Va, Ca2+ ions and phospholipids. In addition to its hemostatic functions, human FXa causes inflammation and induces mitogenesis in several cell types due to its interaction with effector protease receptor-1 (EPR-1). The inter-EGF domain region (L83FTKRL88) of FXa implicated in EPR-1-binding is distinctly different in trocarin (K83VLYQS88). Here we show that, interestingly, trocarin also causes edema in the mouse footpad; the inflammation, accompanied by a large purplish clot, is more persistent than the transient edema caused by FXa. Histological examination indicates significant differences between edema induced by FXa and trocarin. Moreover, trocarin-induced edema is not inhibited by a synthetic peptide based on the FXa-binding region of EPR-1, indicating that the inflammation is probably mediated by a mechanism independent of EPR-1-binding. Trocarin, like FXa, also has a mitogenic effect on bronchial smooth muscle cells mediated by an EPR-1-independent mechanism. Hence trocarin, being closely related to FXa, has similar non-hemostatic functions in mediating inflammation and mitogenesis, yet appears to act by distinctly different mechanisms.

Differentiating between local cytotoxicity, mitogenesis, and genotoxicity in carcinogen risk assessments: the case of vinyl acetate

Understanding the mode of action of carcinogens is critical to scientifically assessing exposure-related risk. Regulatory hazard classification schemes and dose-response assessment paradigms generally require basic knowledge of genotoxic potential to guide decisions on which scheme or paradigm is most appropriate. Although convention suggests that classification and dose-response assessment of genotoxic chemicals should be assessed using conservative assumptions of no threshold, several examples, such as vinyl acetate, exist that challenge this assumption. Vinyl acetate is carcinogenic at portals of entry (nasal cavity and upper gastrointestinal tract). Local metabolism of vinyl acetate produces DNA-reactive acetaldehyde but also produces acetic acid and protons, which contribute to intracellular acidification, cytotoxicity and cell proliferation. This paper reviews their relative contributions to the overall mode of action. Elevated cellular proliferation, well understood to be a risk factor for carcinogenesis, is observed at concentrations associated with tumor formation. Cytotoxicity and compensatory tissue regeneration is one pathway for stimulating cellular proliferation while intracellular acidification is a mitogenic stimulus. Both of these pathways may be operative in nasal tissues while mitogenic proliferation alone appears to be induced in the upper gastrointestinal tract. Using a physiologically-based pharmacokinetic model, quantitative relationships between critical tissue dosimeters and tissue responses are developed to assess the relative importance of genotoxicity and cell proliferation in the overall mode of action of vinyl acetate. This approach supports the concept that intracellular acidification is the sentinel response that precedes cytotoxicity and cellular proliferation. Secondarily, the carcinogenic potential of vinyl acetate is expressed only when tissue exposure to acetaldehyde is high and when cellular proliferation is simultaneously elevated. This mode of action suggests that exposure levels that do not increase intracellular acidification beyond homeostatic bounds will be adequately protective of adverse downstream responses including cancer. These mechanistic insights provide the scientific basis for a cancer classification that incorporates thresholds for cytotoxic and/or mitogenic cell proliferation secondary to intracellular acidification.

Mitogenic effects of Brazilian arthropod venom on isolated islet beta cells: in vitro morphologic ultrastructural and functional studies

BACKGROUND

One of the major pitfalls associated with use of isolated adult islets of Langerhans' cells is their minimal mitotic capacity. Consequently, maintenance of a steady viable islet cell mass is very difficult. To explore how to enhance beta-cell mitogenesis, we have examined the effects of venom fractions extracted from a Brazilian scorpion on morphologic and functional beta-cell patterns. The venom was previously known to induce nesidioblastosis-like effects with chronic hypoglycemia and pancreatitis in animal models.

METHODS

Venom fractions purified from Tityus bahiensis were incubated with batches of isolated rat islets, while a morphologic examination, glucose-stimulated insulin release, insulin content, and insulin messenger ribonucleic acid (mRNA) were carried out early during incubation. On fixation and double fluorescence immunolabeling (rhodamine for anti-insulin monoclonal antibodies; fluorescein for anti-5-bromodeoxyuridine), the preparations were imaged by confocal laser microscopy (CLM) for morphometric quantification of the mitoses. Insulin recovery and mRNA were also assessed at 21 days of culture.

RESULTS

Under CLM examination, the beta-cell mitotic rate significantly rose from 1 to 12.8% for the venom-exposed islets. At day 7, insulin release and content were significantly lower for the venom-exposed than the control islets. However, at day 21 of culture, insulin release in response to static incubation with glucose and insulin mRNA from the venom-exposed islets was higher than controls (p < .05).

CONCLUSIONS

Incubation with the scorpion venom induced a rapid and significant increase in the beta-cell proliferation not associated with a short-term increase in insulin secretion. The latter fully resumed and overcame controls later in culture, possibly after completion of the beta-cell expansion process.

Interleukins 5 and 13 characterize immune responses to respiratory sensitizing acid anhydrides

There is some debate regarding whether occupational asthma induced by respiratory sensitizing acid anhydrides is mediated by the induction of T helper (Th) 2-type responses and the production of IgE, with failure to detect specific IgE antibody in some symptomatic patients. In the current investigations, cytokine secretion profiles induced in draining lymph node cells (LNC) by topical application to BALB/c strain mice of trimellitic anhydride (TMA), phthalic anhydride (PA) and maleic anhydride (MA) have been examined. Responses were compared with those induced by exposure to 2,4-dinitrochlorobenzene (DNCB), a contact allergen that lacks respiratory sensitizing potential. Exposure to all three acid anhydrides stimulated vigorous expression of interleukin (IL)-5, IL-10 and IL-13 but relatively low levels of the type 1 cytokines interferon-gamma (IFN-gamma) and IL-12. In addition, TMA-activated LNC expressed high levels of mitogen-inducible IL-4 whereas MA and PA displayed a lesser potential to elaborate this cytokine. The DNCB-stimulated LNC exhibited the converse type 1 phenotype of cytokine expression. The CD4(+) Th2 cells were the primary source of type 2 cytokines. Respiratory sensitizing acid anhydrides induce a predominantly Th2 cytokine phenotype, including the expression of IL-5 and IL-13, cytokines which in the presence of only very low levels of IL-4 may provide for an IgE-independent mechanism for the development of chemical respiratory allergy. These data provide additional support for the use of cytokine secretion profiling for the prospective identification of chemical respiratory allergens.

Mitogenic potential inducible by He:Ne laser in human lymphocytes in vitro

The objective of the study was to investigate the mitogenic and genotoxic effects of He:Ne laser irradiation (632.8 nm) on human peripheral lymphocytes in vitro. We used the cytokinesis-block micronucleus assay, which incorporates cytochalasin B to inhibit cytokinesis while karyokinesis proceeds normally leading to the appearance of proliferating lymphocytes as binucleated cells. Also micronuclei will appear in cases of genotoxicologically-affected cells. Buffy coat leukocytes were exposed to 10 mW He:Ne laser at energy densities of 1, 2, 3 and 5 J/cm(2). Cells were then cultured in media 199 without any supplementation for 24, 48, 72 and 96 h adding cytochalasin B 24 h before harvesting of cells. Our results showed that laser-induced lymphocytes proliferate throughout the four consecutive days post-laser irradiation. The difference in the frequency of micronuclei between pre- and post-laser irradiation indicates that a He:Ne laser at such energy densities 1, 2, 3 and 5 J/cm(2) does not induce micronucleus formation. These results shed some light on the mechanism encountered by lymphocytes in the process of He:Ne laser-induced biostimulation.

Immunological and physiological effects of chronic exposure of Peromyscus leucopus to Aroclor 1254 at a concentration similar to that found at contaminated sites

Polychlorinated biphenyls (PCBs) are environmental contaminants known to cause adverse health effects to biological systems. Limited data are available on their effects on the immune system of wildlife species. Previously, we found that 4 and 6-week-old white-footed mice (Peromyscus leucopus) born from dams injected with a single dose (300 mg/kg) of Aroclor 1254, had altered immunological, hematological, and biochemical responses. Here, we examined the effect of transplacental, lactational and postnatal exposure to Aroclor 1254, at a concentration similar to that found at contaminated sites, on various physiological parameters of 22-week-old white-footed mice. Liver weight and liver somatic index of PCB treated animals were significantly higher, the combined weights of the adrenal glands were significantly lower and EROD and BROD enzyme activity was significantly higher compared to control values. The number of thymocytes of the treated mice was significantly lower than that of the controls; however, thymocytes of treated mice had a higher proliferative response to the mitogen Con A. These alterations were correlated with the PCBs body burdens. Some toxic effects of chronic exposure to PCBs, at levels comparable to exposure found in contaminated sites in the USA, are still evident in adult P. leucopus.

Immunoregulatory and antioxidant performance of alpha-tocopherol and selenium on human lymphocytes

The role of alpha-tocopherol (alpha-toco) and selenium (Se) on human lymphocyte oxidative stress and T-cells proliferation were studied by flow cytometry. We measured the hydrogen peroxide and glutathione levels in cultured human T-lymphocytes and the proliferation of their subsets: T-helper/inducer, T-suppressor/cytotoxic, and natural killer and interleukin-2 receptors upon stimulation by the mitogens phytohemaglutinin (PHA) and lipopolysaccharide (LPS). The results indicate that early stimulation by mitogens is affected by the glutathione and hydrogen peroxide status of the T-lymphocytes. The addition of 100 microM or 500 microM alpha-toco or 0.5 microM Se alone shows weak antioxidant and immunostimulant properties. When combined, an enhanced antioxidant and immunoregulatory effect was observed. The present findings indicate that alpha-toco and Se have interactive effects as oxygen radical scavengers, thus promoting human lymphocyte response to antigens. This suggests that micronutrient status is an important factor in considering when interpreting the results of in vitro assays of lymphocyte function.

Growth and development in rats given recombinant human epidermal growth factor(1-48) as neonates

To assess effects of supraphysiologic doses of human recombinant epidermal growth factor(1-48) (rhEGF(1-48)) on neonatal rats, 10 litters of Wistar rats/treatment group were given 0 (formulated vehicle), 10, 100, or 1000 microg/kg daily by subcutaneous injection on postnatal days (PND) 1 through 6. Clinical signs, body weight, acquisition of developmental landmarks and reflexes, and behavior were monitored during treatment and for 5 weeks thereafter (to PND 42). A subset of animals was euthanized weekly from PND 7-28 and necropsied. Selected tissues were examined microscopically. Body weight gain at 1000 microg/kg during treatment was significantly less than control. Precocious incisor eruption, eye opening, vaginal opening, and preputial separation occurred at 100 and/or 1000 microg/kg. Acquisition of reflexes (negative geotaxis, wire maneuver, acoustic startle reflex, and visual placing) was delayed at 1000 microg/kg. Acquisition of adult locomotion was also delayed at 1000 microg/kg. These effects were transient, as locomotor activity at PND 28 and 42 did not differ from control. Effects on acoustic-startle responding persisted in females to final assessment on PND 42. Habituation to repeated acoustic stimuli was impaired, as well as response inhibition following a prepulse acoustic stimulus. rhEGF(1-48) induced structural changes in the skin, retina, kidney, oral and nasal mucosa, lung, and liver. Many of these changes were consistent with the expected mitogenic activity of rhEGF(1-48) and were transient in nature, as severity and incidence diminished with time. An exception was changes observed in the retina at 1000 microg/kg (rosettes/folds and focal defects in the outer nuclear/photoreceptor layers) that were still present 3 weeks after termination of treatment. Acceleration of developmental landmarks; suppression of reflexes, behavior, and somatic growth; and mitogenic responses in epidermal tissues have been reported in rodents treated with epidermal growth factor (EGF) derived from various mammalian species. These results demonstrate that a 48-amino acid fragment of human EGF produced by recombinant technology also induces such effects.

Systemic proliferative changes and clinical signs in cynomolgus monkeys administered a recombinant derivative of human epidermal growth factor

Epidermal growth factor (EGF) effects have been explored extensively in vivo in rodents, but little is known about trophic responses in nonhuman primates. A previous publication reports the hyperplastic epithelial/parenchymal changes noted in the digestive tract (tongue, esophagus, stomach, intestine, liver, gallbladder, pancreas, and salivary glands) of adult cynomolgus monkeys treated with recombinant human EGF(1-48) (rhEGF(1-48)). This report documents clinical findings and structural effects in the remaining epithelium-containing tissues of these animals. Two monkeys/sex/dose received rhEGF(1-48) by intravenous bolus at 0 (vehicle), 10, 100, 500 (females only), or 1,000 microg/kg/day (males only) daily for up to 2 weeks. Treatment- and dose-related clinical findings included emesis, fecal alterations (soft feces and diarrhea), lacrimation, nasal discharge, hypoactivity, transient hypotension, and salivation after dosing. Male monkeys administered 1,000 microg/kg became moribund after 5 days of treatment and were necropsied. All other monkeys completed the 2-week treatment period. Necropsy findings in nongastrointestinal tissues were: enlarged, pale kidneys at 100 microg/kg and greater; small thymuses seen sporadically at all doses; and enlarged adrenals and small thyroids in males at 1,000 microqg/kg. Respective organ-to-brain weight ratios at 500 and 1,000 microg/kg for kidneys were 1.5- and 2.6-fold greater and for heart were 1.7- and 1.3-fold greater than controls. Microscopically, pronounced dose-related epithelial hypertrophy and hyperplasia were evident in kidney, urinary bladder, skin (epidermis and adnexa), mammary gland, prostate, seminal vesicles, epididymis, uterus, cervix, vagina, thyroid, thymus, tonsillar crypts, cornea, trachea, and pulmonary airways. Epitheliotrophic effects were conspicuous in many tissues at 100 to 1,000 microg/kg. Changes to renal collecting ducts were present at 10 microg/kg, suggesting that kidneys were a relatively sensitive target. Proliferative alterations were not apparent in testes, intraocular structures, brain ependyma and choroid plexus at any dose. Aside from the noted exceptions, rhEGF(1-48) was a pantrophic epithelial mitogen in cynomolgus monkeys when used intravenously at suprapharmacologic doses.

Mechanisms of cell transformation in the Syrian hamster embryo (SHE) cell transformation system

The Syrian hamster embryo (SHE) cell transformation system has been used for investigational studies of basic mechanisms of neoplastic transformation, as well as determining the carcinogenic potential of chemical, physical, and biological agents. Many of these investigations utilize an intermediate step in the SHE cell neoplastic transformation process, known as morphological transformation, as an indicator that the cells have acquired an increased potential to progress to malignancy. While the nature of the morphologically transformed phenotype is not completely understood, it is believed to result from a block in the cellular differentiation of stem cells present within the SHE cell population. In terms of determination of the transforming potential of biological/chemical/physical agents, more than 500 agents have been tested in the SHE cell transformation assay with an 80-90% correlation between MT and carcinogenic potential. As such, the SHE cell transformation assay has utility as a test to provide short-term information on the carcinogenic potential of chemicals. One class of agents of current interest with regard to SHE cell transformation assay utilization consists of growth and differentiation factors (GDFs). Analysis of the SHE cell transformation potential of the GDFs, epidermal growth factor (EGF), fibroblast growth factor 4 (FGF-4), platelet-derived growth factor AA (PDGF AA), PDGF AB, PDGF BB, and the antimitogenic GDF, transforming growth factor beta one (TGF-beta1), was performed. All GDFs, with the exception of TGF-beta1, induced SHE cell transformation. However, an interesting difference between the GDFs was observed--PDGF A/B and PDGF B/B, but not PDGF A/A, EGF, or FGF-4, induced transformation after both a transient 1-day exposure and a continuous 7-day exposure, while continuous 7-day exposure was required for transformation by PDGF A/A, EGF, and FGF-4. Interestingly, both transient 1-day and continuous 7-day TGF-beta1 exposure resulted in suppression of transformation induced by a variety of transforming agents including growth factors, Ames assay-positive carcinogens, Ames assay-negative carcinogens, and spontaneous transformation. Interestingly TGF-beta1 was not able to suppress transformation by the tumor promoter, TPA. Together, these data demonstrate the utility of the Syrian hamster embryo cell transformation system for analyzing the transforming potential of GDFs and for characterizing differences in transforming mechanisms between different GDFs.

Synergistic teratogenic effects induced by retinoids in mice by coadministration of a RARalpha- or RARgamma-selective agonist with a RXR-selective agonist

To study the interaction of retinoid-induced limb defects and cleft palate on day 11 of gestation, a RXR-selective agonist (AGN191701, an arylpropenyl-thiophene-carboxylic acid derivative, 20 mg/kg orally) was coadministered with a RARalpha-agonist (Am580, an arylcarboxamidobenzoic acid derivative, 5 mg/kg orally) to NMRI mice. AGN191701 was neither fetotoxic nor teratogenic at the dose used but potentiated Am580-induced limb defects and cleft palate and prevented Am580-induced fetal weight retardation. These results suggest that Am580-induced limb defects and probably cleft palate on day 11 of gestation may be mediated via RARalpha-RXR heterodimerization, particularly in the absence of toxicokinetic interactions. AGN191701 was also coadministered with a RARgamma-agonist (CD437, an adamantyl-hydroxyphenyl naphthoic acid derivative, 15 mg/kg orally) on days 8 and 11 of gestation to investigate which CD437-induced defects are mediated via RARgamma-RXR heterodimerization. On day 8 of gestation, AGN191701 potentiated CD437-induced embryolethality, exencephaly, spina bifida aperta, cleft palate, and tail defects, as well as visceral and skeletal defects, but not micrognathia. On day 11 of gestation, the incidence of CD437-induced cleft palate and limb defects was also potentiated when coadministered with the RXR agonist. These results suggest that synergistic teratogenic effects can be induced by coadministration of two receptor-selective retinoids, indicating the importance of RARalpha-RXR and RARgamma-RXR heterodimers in producing structural defects during organogenesis.

Iron, alpha-tocopherol, oxidative damage and micronucleus formation in rat splenocytes

The influence of low and high alpha-tocopherol diets in concert with a high polyunsaturated fat content and a modest increase in dietary iron has been studied. Iron supplementation at five times the recommended dietary level was not associated with any increased sensitivity of the splenocytes to any of the oxidative challenges. Despite the significantly higher alpha-tocopherol concentrations in the plasma and liver of animals supplemented with this vitamin, there was no apparent protection against oxidative genotoxicity, as judged by the formation of micronuclei in splenocytes subjected to oxidative stress ex vivo. These results add to the evidence that vitamin E supplementation has little effect against oxidative genomic damage, at least as demonstrated by an increase in micronucleus frequency.

The superantigenic toxin of Yersinia pseudotuberculosis: a novel virulence factor?

Recently, a superantigenic toxin designated YPM (Yersinia pseudotuberculosis-derived mitogen) was characterized in the supernatant of Y. pseudotuberculosis, a Gram-negative bacterium involved in human enteric infection. To assess the role of YPM in pathophysiology of Y. pseudotuberculosis, a superantigen-deficient mutant was constructed and its virulence was tested in a murine model of infection and compared with the virulence of the wild-type strain (wt). Determination of the survival rate after intravenous inoculation of mice clearly demonstrated a higher survival rate when animals were infected with the superantigen-deficient strain. This decreased virulence of the mutant strain could not be explained by a lower bacterial growth rate in spleen, liver or lung of infected animals. Therefore, production of IFNgamma, TNFalpha, IL-2, IL-6 and IL-10 was followed during the course of infection by cytokine assay in the blood and mRNA detection in the spleen. IL-6 and IFNgamma were the two major cytokines detected whereas TNFalpha production was never observed.

Cell death and cell proliferation in the control of normal and neoplastic tissue growth

The development of reliable methodology for the assessment of rates of cell replication and cell death has enabled the study of how these 2 fundamentally opposed processes work to form and maintain tissue and to remodel tissue following diseases resulting in cell loss. The balance between these 2 processes and the consequences of an imbalance are fundamental to a clearer understanding of how hyperplasia and neoplasia develop in tissues under the influence of chemicals and drugs. An understanding of the changes that occur in target organs and tissues following chemical or drug exposure has enabled a better understanding of the mechanism by which these chemicals are able to induce cancer after prolonged exposure. Studies of the control of cell replication and the changes that occur following drug exposure have defined 2 types of response, 1 in which the cell replicative response is sustained and the other in which the cell replicative response is transient and occurs during the first few days of exposure. Although regulatory and scientific opinion appears ready to accept sustained cell replicative processes as an increased risk factor in the development of cancer, the role played by transient increases in cell replication remains unclear. Concurrent events in target organs following treatment with chemicals that induce transient increases in cell replication have revealed that the rates of apoptosis are suppressed at the same time as the cell replication levels are induced. Additional evidence suggests that growth and antigrowth factors are central in controlling these responses. Escape from the regulatory action of these factors is postulated to be one of the ways in which nongenotoxic carcinogenic chemicals, such as the peroxisome proliferators and sodium phenobarbitone, may induce cancer, with apoptosis playing a key role in the process.

Gabapentin-induced mitogenic activity in rat pancreatic acinar cells

Gabapentin induces pancreatic acinar cell tumors in rats through unknown, yet apparently nongenotoxic mechanisms. The primary objective of this study was to determine whether gabapentin acts as a tumor promoter by stimulating acinar cell proliferation in rat pancreas. To this end, indices of pancreatic growth, including increased pancreatic weight, stimulation of acinar cell proliferation, and/or enhanced expression of immediate-early oncogenes were monitored in rats given gabapentin in the diet at 2 g/kg/day for up to 12 months. Rats fed raw soy flour (RSF), a known inducer of pancreatic acinar cell tumors through cholecystokinin-mediated mitogenic stimulation, were used throughout as positive controls. In addition, recent data suggests that gabapentin binds to the alpha(2)delta subunit of a voltage-gated, L-type calcium channel. Because signaling pathways for proliferative processes in pancreatic acinar cells involve intracellular calcium mobilization, the effects of gabapentin on intracellular calcium mobilization ([Ca(2+)](i)) and (3)H-thymidine incorporation were investigated in pancreatic acinar cells isolated from normal rat pancreas and in the AR42J rat pancreatic tumor cell line. As indicated by BrdU labeling indices, acinar cell proliferation increased 3-fold by Day 3 of RSF treatment and remained slightly greater than controls throughout the experiment. Pancreatic weights of RSF-fed rats were 32 to 56% greater than controls throughout the experiment. In contrast, gabapentin had no effect on pancreatic weight or acinar cell labeling index, and therefore had no apparent effect on pancreatic growth. In isolated pancreatic acinar cells, however, gabapentin induced mobilization of intracellular calcium and caused a slight increase in (3)H-thymidine incorporation. The data suggest that gabapentin may possess low level mitogenic activity, which is not easily detectable in in vivo assays.

Heregulin enhances regenerative proliferation in postnatal rat utricular sensory epithelium after ototoxic damage

Hair cell loss due to acoustic and ototoxic damage often leads to hearing and balance impairments. Although a spontaneous event in chicks and lower vertebrates, hair cell replacement occurs at a much lower frequency in mammals presumably due to a very low rate of supporting cell proliferation following injury. We report here that heregulin, a member of the neuregulin family, dramatically enhances proliferation of supporting cells in postnatal rat utricular epithelial sheet cultures after gentamicin treatment, as revealed by bromo-deoxyuridine (BrdU) immunocytochemistry. A dose-dependent study shows that the maximal effects of heregulin are achieved at 3 nM. The mitogenic effects of heregulin are confirmed in utricular whole mount cultures. Autoradiography of the utricular whole mount cultures shows that heregulin also enhances the number of tritiated thymidine-labeled cells within the hair cell layer. TaqMan quantitative RT-PCR analysis and immunocytochemistry reveal that heregulin and its binding receptors (ErbB-2, ErbB-3 and ErbB-4) are expressed in the inner ear sensory epithelium. Of several ligands activating various ErbB receptors, including heregulin, neuregulin-3, beta-cellulin, heparin binding-epidermal growth factor (HB-EGF), transforming growth factor-alpha (TGF-alpha) and EGF, heregulin shows the most potent mitogenic effects on supporting cells. Because neuregulin-3 that signals only through ErbB-4 does not show an effect, these data suggest that activation of the ErbB-2-ErbB-3 heterodimeric complexes, rather than ErbB-4, is critical for the proliferative response in the utricular sensory epithelium. In addition, gentamicin treatment induces an upregulation of heregulin mRNA. Considered together, heregulin may play an important role in hair cell regeneration following ototoxic damage.

The extracellular signal-regulated kinase pathway contributes to mitogenic and antiapoptotic effects of peroxisome proliferators in vitro

Peroxisome proliferators are a class of nongenotoxic rodent hepatocarcinogens thought to induce tumors by altering the balance between mitosis and apoptosis. Previous studies suggest mitogenic growth factors that act through the extracellular signal-regulated kinase (ERK) pathway, including insulin and epidermal growth factor (EGF), modulate peroxisome proliferator-activated receptor alpha activation as well as the mitogenic activity of peroxisome proliferators. We have investigated whether the ERK pathway plays a role in regulating the growth and survival altering properties of peroxisome proliferators in primary mouse hepatocytes. Exposure of hepatocytes to Wy-14,643 and trichloroacetate resulted in a dose-dependent phosphorylation and activation of ERK. Peroxisome proliferator-induced ERK phosphorylation was blocked when cells were pretreated with the MEK (ERK kinase) inhibitor, PD098059, or the phosphatidyl-inositol 3-kinase (PI3K) inhibitors, LY294002 and apigenin, suggesting that both MEK and PI3K are involved in the initial response. The pathway leading to peroxisome proliferator-induced ERK activation is different than that induced by phorbol ester or EGF, since the PI3K inhibitors had no effect on ERK phosphorylation induced by these agents. Under defined culture conditions, Wy-14,643 increased the level of BrdU incorporation in primary hepatocytes and suppressed the incidence of apoptosis induced by transforming growth factor beta 1. In contrast, concentrations of PD098059 that block Wy-14,643-induced ERK phosphorylation also blocked the stimulation of DNA replicative synthesis and suppression of apoptosis by Wy-14,643. These studies indicate that activation of the ERK pathway through a PI3K-dependent mechanism may play a significant role in the tumor-promoting properties of peroxisome proliferators.

FGF7/KGF triggers cell transformation and invasion on immortalised human prostatic epithelial PNT1A cells

Fibroblast growth factor 7 (FGF7/KGF) is synthesized exclusively by fibroblasts in normal tissues; it acts as a potent mitogen on epithelial cells, through interaction with the FGF7-specific receptor FGFR2/IIIb. To examine the importance of this growth factor both to prostate physiology and to prostate-cancer progression, we have tested the exogenous effect of FGF7. Thus, by mimicking the paracrine pathway (on proliferation, growth in soft agar and invasion) on the human prostatic epithelial cell line PNT1A positively checked for FGFR2/IIIb expression, FGF7 significantly enhanced cell proliferation at an optimal concentration of 7.5 x 10(-11) M, but no significant invasion or growth in soft agar were observed. To confirm FGF7 properties on human prostatic epithelial cells, we constitutively expressed FGF7 by transfecting PNT1A cells with FGF7-cDNA. The FGF7-transfected clones, PNT1A/ FGF7-T5 and PNT1A/FGF7-T6, were stable and expressed FGF7. Analysis of the FGF7-autocrine loop on the non-tumorigenic epithelial cells PNT1A showed acquired invasive potential in in vitro extracellular-matrix migration assays, specifically inhibited by an FGF7-neutralizing antibody, and over-expressed factors implicated in the migration process: the metalloproteinase MMP-1 and the plasminogen activator uPA. Taken together, these results demonstrate a role for FGF7 in triggering invasion of human prostatic epithelial cells. Furthermore, these FGF7-transfected clones exhibited functional and physiological differences from the original PNT1A cell line: anchorage-independent growth, growth in serum-free media and increased proliferation. These data confirm the oncogenic function of FGF7 in prostate progression potentially acting through paracrine and/or autocrine regulatory pathways.

Application of oligo-(14-amino-3,6,9,12-tetraoxatetradecanoic acid) lipid conjugates as steric barrier molecules in liposomal formulations

Lipid conjugates of oligo-(14-amino-3,6,9,12-tetraoxatetradecanoic acid) (ATTAn) were synthesized as monodisperse analogues of poly(ethylene glycol) (PEG) derivatives used in liposomal drug delivery systems. The new lipids were shown to be at least equivalent to MePEGA-2000-DSPE in assays designed to evaluate the effectiveness of polymers as steric barrier molecules in liposomes. Liposomes containing 1-5% of ATTA8-DSPE (octamer) showed comparable long circulation behavior relative to PEG-2000-DSPE analogues. Surprisingly, the shorter ATTA4-DSPE (tetramer) appeared to be quite effective in reducing clearance. Liver enzyme levels and systemic single dose tolerability of ATTA8-DSPE liposomes were comparable to controls, suggesting that the new materials are nontoxic. Prolonged exposure of ATTA8-DSPE liposomes to splenocytes in vitro showed no evidence of mitogenicity relative to controls or MePEGA-2000-DSPE liposomes. ATTA8-DSPE was as effective as MePEGC-2000-DSPE in preventing complement activation by cationic liposome systems. Repeat dosage in vivo regimes in ICR mice using DSPC/cholesterol liposomes, with and without 5% ATTA8-DSPE and MePEGC-2000-DSPE, showed no evidence of enhanced clearance on successive doses. Splenocytes recovered after repeat doses showed no significant evidence of mitogenicity on restimulation with liposomes. Cellular differentiation and activation marker levels in splenocytes recovered after the fourth in vivo administration were at normal levels. These results suggest that ATTAn oligomers do not induce an immune response in isolation. It was demonstrated that ATTA8-DSPE could be used to replace PEG-lipids in the formulation of doxorubicin, plasmid DNA and oligonucleotides using a variety of formulation techniques. The study demonstrates that ATTAn oligomers can be safely and effectively used in place of poly(ethylene glycol) as well-defined biomaterials in liposomal applications where reproducible behavior is critical.

Differential effects of B- and T-lymphocyte mitogens on cytochrome P450 in mice

Lipopolysaccharide (LPS) is widely used as a B-lymphocyte mitogen and is known to depress expression of the cytochrome P450 (P450). However, there have been no studies regarding to the effects of the other mitogens on the expression of P450. This study investigated the effects of mitogens on the constitutive and inducible expression of mouse hepatic P450. Following treatment with B-lymphocyte mitogens, such as LPS and pokeweed mitogen (PWM), hepatic P450 content was reduced. LPS and PWM also suppressed activities of microsomal ethoxyresorufin O-deethylase, pentoxyresorufin O-dealkylase and aniline hydroxylase, a representative activity of P4501A1/2, P4502B1/2 and P4502E1, respectively, in both constitutive and P450 induced mice. However, there was no effect when treated with T-lymphocyte mitogens, such as concanavalin A and phytohemagglutinin. Suppression of P450 expression in the LPS- or PWM-treated mice occurred and was shown to involve a decrease in P450 protein and mRNA levels in liver. These results suggest that suppressive effects of mitogens on the expression of P450 might be different and that B-lymphocyte mitogens selectively depress the expression of P450.

Peroxisome proliferator-activated receptors (PPARS) and carcinogenesis

Peroxisome proliferators (PPs) are an important group of chemicals that include certain hypolipidemic drugs, plasticizers and pollutants. Many of these agents are known rodent liver tumor promoters and debate exists as to whether humans are at increased cancer risk following exposure to PPs. Research over the last decade has focused on determining the biochemical and molecular mechanisms by which peroxisome proliferators exert their effects, in the hope that this controversy will be settled. PPs regulate gene expression via a steroid hormone receptor, the peroxisome proliferator-activated receptor (PPAR). At least three subtypes of PPAR (alpha, beta and gamma) have been cloned from several species, including humans. These receptors have been implicated in tumor promotion, cellular differentiation, and apoptosis. In the present article, the current understanding of how PPARs are involved in tumorigenesis, and what this may mean to human risk assessment, will be discussed.

Specific binding and growth-promoting activity of insulin in endometrial cancer cells in culture

OBJECTIVE

Insulin is known to be mitogenic to a variety of cells in culture. The purpose of this study was to investigate the possible role of insulin in the growth and development of endometrial cancers.

STUDY DESIGN

Specific binding and growth effects of insulin were studied in 5 different human endometrial cancer cell lines derived from cancers with different degrees of differentiation: HEC-1-A and HEC-1-B (from a moderately well-differentiated adenocarcinoma), RL95-2 (from a moderately well-differentiated adenosquamous carcinoma), KLE (from poorly differentiated carcinoma), and AN3 CA (from a metastatic undifferentiated endometrial carcinoma). The receptors were further characterized by competitive binding and chemical cross-linking studies.

RESULTS

Binding studies with 125I-insulin revealed the presence of high-affinity binding sites for insulin on all the 5 cell lines. Binding of insulin was found to be highly specific. Competitive binding studies with 125I-insulin revealed that insulin was most effective in displacing the labeled hormone, whereas insulin-like growth factor-I and insulin-like growth factor-II competed for binding only at very high concentrations. Scatchard analysis of the binding data revealed that the association constant for the high-affinity binding sites ranged from 0.72 to 1.91 x 10(9) L/mol. Estrogen-receptor-negative cell lines HEC-1-A and HEC-1-B had the highest number of insulin receptors, whereas the estrogen-receptor-positive cell line RL95-2 had the least number of receptors. The effect of insulin on cell proliferation was studied by monitoring cell number and incorporating [3H]thymidine into deoxyribonucleic acid of the cells. Insulin stimulated cell growth of all the cell lines.

CONCLUSIONS

The results of this study indicate the potential role of hyperinsulinemia in the growth and development of endometrial cancer.

Repair of wounded monolayers of cultured vascular endothelial cells after simultaneous exposure to lead and zinc

We investigated the interaction between lead and zinc on the repair of wounded monolayers of cultured bovine aortic endothelial cells. A half area of the monolayers was wounded and then incubated in the presence of lead (5.0 and 10 microM) and/or zinc (10 microM). It was morphologically observed that the appearance of the cells in the wounded area was strongly decreased by lead alone but considerably increased by zinc alone. The repair of wounded area after simultaneous exposure to lead and zinc showed that lead inhibits not only spontaneous but also zinc-promoted repair of endothelial cell layers without a change of the leakage of lactate dehydrogenase. Interaction between lead and zinc on the DNA synthesis of growing endothelial cells was similar to that on the repair, suggesting that the repair reflected the proliferation. In growing endothelial cells, the intracellular accumulation of lead was significantly increased by zinc; that of zinc was unaffected by lead; and that of metallothionein was slightly increased by zinc and lead but the effect of zinc was suppressed in the presence of lead. Although zinc significantly decreased the intracellular accumulation of radioactive calcium, lead increased it in the presence or absence of zinc. It was therefore concluded that lead inhibits not only spontaneous but also zinc-promoted repair of the damaged endothelial cell layers through an inhibition of the proliferation mediated by the calcium-mediated signalling pathways and/or a disturbance of intracellular calcium homeostasis.

Cytotoxicity and mitogenicity of adenosine triphosphate in the cochlea

Evidence is accumulating to indicate that extracellular adenosine 5'-triphosphate (ATP) may function as a neurotransmitter, neuromodulator, cytotoxin and mitogen. Many of the cells in the cochlea have ATP receptors, however, their function is unknown. The purpose of the present study was to test whether ATP may act as a cytotoxin in the cochlea. ATP was applied to acutely isolated outer hair cells (OHCs) and their shape changes monitored. In addition, ATP was applied into the cochlea by perfusion of the perilymph compartment for 2 h and the animals allowed to survive 3-4 weeks post drug application. At this time, sound-evoked cochlear potentials and distortion product otoacoustic emissions (DPOAEs) were monitored and the cochleas evaluated histologically. Results indicate that when applied to isolated OHCs, ATP (3-30 mM) induced a bleb formation in the infracuticular region of the cell that burst within a few minutes. Short OHCs were more sensitive to this effect of ATP than long OHCs. 3-4 weeks after the perilymph perfusion of ATP (60 mM; 2 h) cochlear potentials and DPOAEs were abolished, and histologically, cells in the organ of Corti and the stria vascularis were found to have been destroyed. In addition, there was loss of spiral ganglion cells and proliferating connective tissue filled varying proportions of the scala tympani and vestibuli. Application of sodium gluconate, a control, at the same concentrations had no effect either on the isolated OHCs or when applied in vivo. Results suggest that extracellular ATP or a metabolic product may act as a cytotoxin to some epithelial and neural elements in the cochlea and possibly as a mitogen to mesenchymal cells or fibrocytes.

Expression of the immediate-early genes, c-fos, c-jun, and c-myc: a comparison in rats of nongenotoxic hepatocarcinogens with noncarcinogenic liver mitogens

The involvement of the immediate-early (IE) genes c-fos, c-jun, and c-myc in regenerative liver hyperplasia is accepted, but their involvement in direct hyperplasia is uncertain. We have examined the hypothesis that the ability to induce IE genes may reflect the hepatocarcinogenic potential of a chemical. The ability of 1,4-dichlorobenzene (DCB) (300 mg/kg) (a noncarcinogenic rat liver mitogen), diethylhexyl phthalate (DEHP) (950 mg/kg), and chlorendic acid (120 mg/kg) (both nongenotoxic hepatocarcinogens) to induce c-fos, c-jun, and c-myc expression in rat liver was determined by Northern blot analysis and by in situ hybridization. Results were correlated to hepatic labeling index (LI) as determined by incorporation of BrdU in each of three lobes for each of three male F344 rats per group. Carbon tetrachloride (CCl4) (2 ml/kg) was used as a positive control. Increased LI was preceded by elevated expression of all three IE genes after CCl4, but also after DCB and DEHP, although induction by these was less marked. In all cases, there was considerable interanimal variation within groups, but little interlobe variation. Interestingly, there was a good correlation (r2 > or = 0.85) between c-myc expression and LI, but not between LI and c-fos or c-jun. Despite the disparate carcinogenic potential of DEHP and DCB, both chemicals induced similar patterns of IE gene expression, suggesting that this cannot distinguish hepatocarcinogenic liver mitogens from noncarcinogenic liver mitogens. These data assist in the evaluation of IE gene expression both as a marker of direct versus regenerative hyperplasia and as an indicator of the hepatocarcinogenic potential of liver mitogens.

Hepatic ploidy, nuclearity, and distribution of DNA synthesis: a comparison of nongenotoxic hepatocarcinogens with noncarcinogenic liver mitogens

Most nongenotoxic hepatocarcinogens such as diethylhexyl phthalate (DEHP) and chlorendic acid (CEA) induce hepatocyte replicative DNA synthesis. However, not all mitogens are carcinogenic; in National Toxicology Program (NTP) studies 1,4-dichlorobenzene (DCB) was not hepatocarcinogenic in the rat despite the induction of substantial hepatic DNA synthesis. We have examined the hypothesis that the profile of hepatocyte labeling index (LI) may dictate hepatocarcinogenic potential. Using flow cytometry, we investigated the effects of DEHP, CEA, and DCB on hepatocyte ploidy, nuclearity, and LI distribution among the ploidy/nuclearity classes in male Fischer 344 rats. Dosing was for 7 days at the dose and route employed previously in the NTP cancer bioassays. Unlike DEHP and CEA, DCB reduced the proportion of tetraploid cells (4N plus 2 x 2N) and increased the proportion of mononucleated octoploid (8N) cells. DCB and DEHP increased the mean hepatic LI (17 +/- 2 and 23 +/- 3%, respectively, compared with 1.4 +/- 0.4% in controls), whereas, as expected for a chronic inducer of S-phase, CEA did not. LI was increased in all hepatocyte ploidy/nuclearity classes except the binucleated tetraploid cells (2 x 2N) and was elevated most in the mononucleated octoploid population (8N) (LI = 44 +/- 11, 49 +/- 14, and 1.3 +/- 0.4% of 8N hepatocytes for DCB, DEHP, and control, respectively). In general, the effects of DCB on LI could not be distinguished from those of DEHP. However, DEHP tended to induce DNA synthesis in a greater proportion of 2N and 2 x 4N cells; future studies will analyze whether the induction of DNA synthesis in these small populations may be more relevant to hepatocarcinogenesis.

Xwnt-8 and lithium can act upon either dorsal mesodermal or neurectodermal cells to cause a loss of forebrain in Xenopus embryos

When Xenopus gastrulae are made to misexpress Xwnt-8, or are exposed to lithium ions, they develop with a loss of anterior structures. In the current study, we have characterized the neural defects produced by either Xwnt-8 or lithium and have examined potential cellular mechanisms underlying this anterior truncation. We find that the primary defect in embryos exposed to lithium at successively earlier stages during gastrulation is a progressive rostral to caudal deletion of the forebrain, while hindbrain and spinal regions of the CNS remain intact. Misexpression of Xwnt-8 during gastrulation produces an identical loss of forebrain. Our results demonstrate that lithium and Wnts can act upon either prospective neural ectodermal cells, or upon dorsal mesodermal cells, to cause a loss of anterior pattern. Specifically, ectodermal cells isolated from lithium- or Wnt-exposed embryos are unable to form anterior neural tissue in response to inductive signals from normal dorsal mesoderm. In addition, although dorsal mesodermal cells from lithium- or Wnt-exposed embryos are specified properly, and produce normal levels of the anterior neural inducing molecules noggin and chordin, they show a greatly reduced capacity to induce anterior neural tissue in conjugated ectoderm. Taken together, our results are consistent with a model in which Wnt- or lithium-mediated signals can induce either mesodermal or ectodermal cells to produce a dominant posteriorizing morphogen which respecifies anterior neural tissue as posterior.

Liver cell proliferation induced by nafenopin and cyproterone acetate is not associated with increases in activation of transcription factors NF-kappaB and AP-1 or with expression of tumor necrosis factor alpha

Our previous studies have shown a different pattern of immediate early gene and growth factor gene expression between compensatory liver regeneration occurring after cell loss/death and direct hyperplasia induced by primary mitogens. In the present study, modifications in the activation of two transcription factors, NF-kappaB and AP-1; steady-state levels of tumor necrosis factor alpha (TNF-alpha) messenger RNA (mRNA); and induction of the inducible nitric oxide synthase (iNOS) were examined in rat liver during different types of cell proliferation. Compensatory regeneration was induced in male Wistar rats by partial hepatectomy of two thirds (PH) or a necrogenic dose of CCl4 (2 mL/kg), whereas direct hyperplasia was induced by a single administration of the primary mitogens lead nitrate (LN, 100 micromol/kg), cyproterone acetate (CPA, 60 mg/kg), or nafenopin (NAF, 200 mg/kg). Liver regeneration after treatment with CCl4 was associated with an increase in steady-state levels of TNF-alpha mRNA, activation of NF-kappaB and AP-1, and induction of iNOS. A strong and prolonged activation of NF-kappaB but not of AP-1 was observed in LN-induced hyperplasia. LN also induced an increase in hepatic levels of TNF-alpha and iNOS mRNA. On the other hand, direct hyperplasia induced by two other primary mitogens, NAF and CPA, occurred in the complete absence of modifications in the hepatic levels of TNF-alpha mRNA, activation of NF-kappaB and AP-1, or induction of iNOS, although the number of hepatocytes entering S phase 18 to 24 hours after NAF was similar to that seen after PH. These results add further support to the hypothesis that cell proliferation occurring in the absence of cell loss/death may be triggered by unknown signaling pathways different from those responsible for the transition of hepatocytes from G0 to G1 after PH or cell necrosis.