Tumour necrosis factor-alpha enhances cAMP-induced programmed cell death in mouse thymocytes

Inhibition of the GTPase Rac1 mediates the antimigratory effects of metformin in prostate cancer cells

Cell migration is a critical step in the progression of prostate cancer to the metastatic state, the lethal form of the disease. The antidiabetic drug metformin has been shown to display antitumoral properties in prostate cancer cell and animal models; however, its role in the formation of metastases remains poorly documented. Here, we show that metformin reduces the formation of metastases to fewer solid organs in an orthotopic metastatic prostate cancer cell model established in nude mice. As predicted, metformin hampers cell motility in PC3 and DU145 prostate cancer cells and triggers a radical reorganization of the cell cytoskeleton. The small GTPase Rac1 is a master regulator of cytoskeleton organization and cell migration. We report that metformin leads to a major inhibition of Rac1 GTPase activity by interfering with some of its multiple upstream signaling pathways, namely P-Rex1 (a Guanine nucleotide exchange factor and activator of Rac1), cAMP, and CXCL12/CXCR4, resulting in decreased migration of prostate cancer cells. Importantly, overexpression of a constitutively active form of Rac1, or P-Rex, as well as the inhibition of the adenylate cyclase, was able to reverse the antimigratory effects of metformin. These results establish a novel mechanism of action for metformin and highlight its potential antimetastatic properties in prostate cancer.

Apoptosis and inflammation

During the last few decades it has been recognized that cell death is not the consequence of accidental injury, but is the expression of a cell suicide programme. Kerr et al. (1972) introduced the term apoptosis. This form of cell death is under the influence of hormones, growth factors and cytokines, which depending upon the receptors present on the target cells, may activate a genetically controlled cell elimination process. During apoptosis the cell membrane remains intact and the cell breaks into apoptotic bodies, which are phagocytosed. Apoptosis, in contrast to necrosis, is not harmful to the host and does not induce any inflammatory reaction. The principal event that leads to inflammatory disease is cell damage, induced by chemical/physical injury, anoxia or starvation. Cell damage means leakage of cell contents into the adjacent tissues, resulting in the capillary transmigration of granulocytes to the injured tissue. The accumulation of neutrophils and release of enzymes and oxygen radicals enhances the inflammatory reaction. Until now there has been little research into the factors controlling the accumulation and the tissue load of granulocytes and their histotoxic products in inflammatory processes. Neutrophil apoptosis may represent an important event in the control of intlamtnation. It has been assumed that granulocytes disintegrate to apoptotic bodies before their fragments are removed by local macrophages. Removal of neutrophils from the inflammatory site without release of granule contents is of paramount importance for cessation of inflammation. In conclusion, apoptotic cell death plays an important role in inflammatory processes and in the resolution of inflammatory reactions. The facts known at present should stimulate further research into the role of neutrophil, eosinophil and macrophage apoptosis in inflammatory diseases.

Modulating effects of nonselective and selective phosphodiesterase inhibitors on lymphocyte subsets and humoral immune response in mice

Phosphodiesterase (PDE) inhibitors can regulate the activity of immune cells by increasing intracellular levels of cyclic nucleotides. The aim of this study was to determine the effects of milrinone, a selective PDE3 inhibitor, sildenafil, a selective PDE5 inhibitor, and aminophylline, a nonselective PDE inhibitor, on lymphocyte subsets and humoral immune response in mice when administered in vivo. Aminophylline (20 mg/kg, i.m.), milrinone (1 mg/kg, i.m.) or sildenafil (1 mg/kg, p.o.) were administered to mice either once or five times at 24 h intervals. Some mice were immunized with a sheep red blood cell (SRBC) suspension administered i.p. either 2 h after the single dose or 2 h after the second of the five doses. In non-immunized mice treated five times with PDE inhibitors, the subsets of T lymphocytes in the thymus and T and B lymphocytes in the spleen and mesenteric lymph nodes were determined 12, 24 or 72 h after the last dose. The humoral immune response was determined on days 4, 7 and 14 after SRBC injection in SRBC-immunized mice treated with PDE inhibitors. A modulating effect of the drugs on lymphocyte subpopulations was observed. The greatest impact was observed in splenocyte subpopulations, and resulted in decreased percentages of B cells (CD19(+)) and increased percentages of T cells (CD3(+), CD4(+), CD8(+)). No effect or slight influence of the drugs on anti-SRBC hemagglutinins was observed, but the number of plaque-forming splenocytes was increased. The drugs under investigation did not show a significant immunosuppressive effect.

Expression of tumour necrosis factor-alpha is associated with apoptosis in lungs of pigs experimentally infected with porcine reproductive and respiratory syndrome virus

Expression of tumour necrosis factor (TNF)-alpha and its association with apoptosis was examined in lungs from pig experimentally inoculated with porcine reproductive and respiratory syndrome virus (PRRSV). The TNF-alpha nucleic acid was detected in PRRSV-infected alveolar macrophages by reverse transcription-polymerase chain reaction (RT-PCR). The TNF-alpha antigen was detected in alveolar macrophages by immunohistochemisty. DNA fragmentation in apoptotic cells was detected by in situ terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling (TUNEL). A double-labelling procedure using immunohistochemisty for the detection of PRRSV and the in situ TUNEL assay for the detection of apoptosis demonstrated that a majority of labelled cells were infected with PRRSV or apoptotic, but not both. Apoptotic cells were more abundant than PRRSV-infected cells in all lungs examined. A double-labelling procedure using immunohistochemisty for the detection of TNF-alpha and the in situ TUNEL assay for the detection of apoptosis demonstrated that a majority of labelled cells were apoptotic or for TNF-alpha, but not both. These data suggested that TNF-alpha released from macrophages after infection by PRRSV may induce apoptosis in uninfected bystander cells.

Mycoplasma bovis induces apoptosis of bovine lymphocytes

We report Mycoplasma bovis induces apoptotic death of bovine lymphocytes. Using flow cytometry analyzed propidium iodide inclusion we observed a loss in viable lymphocytes upon incubation of freshly isolated bovine PBMCs with M. bovis. The use of annexin V staining as well as TUNEL assays corroborated these findings. In addition, these assays indicated that the M. bovis induced lymphocyte death is apoptotic in nature. Subsequent experiments demonstrated that the prokaryotic protein production inhibitor chloramphenicol inhibited lymphocyte death induced by M. bovis, showing that M. bovis protein production is necessary for the induction of lymphocyte death, and that the death is not dependent upon the addition of apoptotic inducers as shown with other mycoplasmas. We also show that M. bovis is different from other bovine mycoplasmas (both pathogenic and non-pathogenic) with regards to this characteristic.

cAMP-induced apoptosis in granulosa cells is associated with up-regulation of P53 and bax and down-regulation of clusterin

Evidence indicates that cAMP induces apoptosis in granulosa cells of rat and human ovary. The mechanism by which cAMP induces apoptosis is not known. This study was carried out to evaluate changes in expression of cell death promoters, P53 and bax, and cell death repressor, bcl-2, in cAMP-treated granulosa cells. Treatment of granulosa cells with forskolin (FSK), or 8-bromo-cAMP induced apoptosis as evidenced by internucleosomal DNA fragmentation and chromatin condensation as revealed by gel electrophoresis and fluorescent DAPI staining, respectively. The apoptotic effect of cAMP was accompanied by an increase in the expression of P53 and bax proteins as evaluated by Western blot and immunocytochemistry. No change in bcl-2 protein level was observed in cAMP-treated granulosa cells as compared to control. These data suggest that cAMP may activate apoptosis in granulosa cells by shifting the ratio of the death promoter to death repressor genes via alteration of P53 and bax expression. cAMP was also shown to inhibit gene expression of clusterin, an apoptosis-associated protein, suggesting a role for this protein in cAMP-induced apoptosis in granulosa cells. The data of the present study provide a basis for future studies to elucidate the molecular mechanism of follicular atresia and regulation of apoptotic cell death in ovarian follicles.

Inhibition of tumor necrosis factor-alpha induced neutrophil apoptosis by cyclic AMP: involvement of caspase cascade

Treatment of neutrophils with tumor necrosis factor-alpha (TNF-alpha) in the presence of cycloheximide induced apoptosis within 3 h, as evaluated by the occurrence of morphological nuclear changes characteristic of apoptosis. Pretreatment of neutrophils with dibutyryl cyclic AMP (dbcAMP) suppressed the TNF-alpha/cycloheximide-induced apoptosis in neutrophils in a concentration-dependent manner, while dbcAMP by itself did not induce any morphological changes. Forskolin, or a phosphodiesterase inhibitor, also produced a concentration-dependent inhibition on apoptosis. This inhibition by dbcAMP was completely reversed by pretreatment with the protein kinase A inhibitor, N-[2-(p-bromocinnamylamino) ethyl]-5-isoquinoline sulphonamide (H-89). DbcAMP also inhibited the TNF-alpha/cycloheximide-induced activation of caspase-3, but it had no effect on the activation of caspase-8 in human neutrophils. Furthermore, dbcAMP did not directly inhibit activated caspase-3 activity. Inhibitor of protein kinase C, phosphatidylcholine-specific phospholipase C, tyrosine kinase, nitric oxide synthase, or granulocyte colony-stimulating factor or granulocyte monocyte colony-stimulating factor did not affect apoptosis. These results indicate that the elevation of levels of endogenous intracellular cyclic AMP and subsequent activation of protein kinase A play a crucial role in the prevention of apoptosis triggered by TNF-alpha/cycloheximide in human neutrophils, and that the possible target of cyclic AMP is a product in the metabolic pathway between caspase-8 and caspase-3.

Involvement of peritoneal macrophage in the induction of cytotoxicity due to apoptosis in ascitic fluid associated with severe acute pancreatitis

The aim of this study was to assess the significance of peritoneal macrophage in inducing cytotoxicity in ascitic fluid associated with severe acute pancreatitis. The involvement of peritoneal macrophage was examined experimentally in rats by macrophage depletion with peritoneal lavage prior to the development of pancreatitis. More than 94% of the cellular components collected from peritoneal cavities by the lavage are macrophages. Although the ascitic fluid collected from the rats with necrotizing pancreatitis showed cytocidal effects via apoptosis on Madin-Darby canine kidney cells in a dose- and time-dependent manner, cytotoxicity or apoptosis-inducing activity almost disappeared from the ascitic fluid by the preceding peritoneal lavage. The ascitic fluid did not show significant differences by the lavage in osmolarity and in concentrations of albumin, bilirubin, amylase, and lipase. Although a slight reduction of tumor necrosis factor-alpha was noted with the lavage, tumor necrosis factor-alpha failed to induce apoptotic cell death in the cells, and the neutralization by antibody ameliorated neither cell death nor apoptosis. We conclude that peritoneal macrophages secrete apoptosis-inducing factor(s) into pancreatitis-associated ascitic fluid, other than tumor necrosis factor-alpha.

beta2-adrenergic receptor-selective agonist clenbuterol prevents Fas-induced liver apoptosis and death in mice

Stimulation of the cAMP-signaling pathway modulates apoptosis in several cell types and inhibits Jo2-mediated apoptosis in cultured rat hepatocytes. No information is yet available as to whether the hepatic beta2-adrenergic receptor (AR) expression level, including beta2-AR-dependent adenylyl cyclase activation, modulates hepatocyte sensitivity to apoptosis in vivo or whether this sensitivity can be modified by beta2-AR ligands. We have examined this using C57BL/6 mice, in which hepatic beta2-AR densities are low, and transgenic F28 mice, which overexpress beta2-ARs and have elevated basal liver adenylyl cyclase activity. The F28 mice were resistant to Jo2-induced liver apoptosis and death. The beta-AR antagonist propranolol sensitized the F28 livers to Jo2. In normal mice clenbuterol, a beta2-AR-specific agonist, considerably reduced Jo2-induced liver apoptosis and death; salbutamol, another beta2-AR-selective agonist, also reduced Jo2-induced apoptosis and retarded death but with less efficacy than clenbuterol; and propranolol blocked the protective effect of clenbuterol. This indicates that the expression level of functional beta2-ARs modulates Fas-regulated liver apoptosis and that this apoptosis can be inhibited in vivo by giving beta2-AR agonists. This may well form the basis for a new therapeutic approach to diseases involving abnormal apoptosis.

The three isoforms of transforming growth factor-beta co-stimulate rat T cells and inhibit lymphocyte apoptosis

In this study the three different mammalian isoforms of transforming growth factor-beta (TGF-beta) were compared with regard to their effect on the response of rat T lymphocytes to the superantigen, staphylococcal enterotoxin A (SEA). All different isozymes were found to increase the proliferative response of rat T lymphocytes, which was accompanied by a significantly lower percentage of apoptotic cells than proliferation in the absence of TGF-beta. The same effect of TGF-beta was observed on the generation of apoptotic cells in an allo response (mixed lymphocyte reaction). TGF-beta2 and TGF-beta3 were three to 10-fold more potent than TGF-beta1 as co-stimulators of T lymphocytes, and equal in decreasing the percentage of apoptotic T cells. TGF-beta1 reduced the frequency and the number of cells undergoing apoptosis in T cells and, to an even higher degree, among B lymphocytes. TGF-beta did not seem to affect the production of the apoptosis inducer, tumour necrosis factor-alpha (TNF-alpha), neither at the mRNA level nor at the protein level. Neutralizing antibodies against the cytokine, TNF-alpha, decreased the percentage of apoptotic cells among T cells responding to SEA, both in the absence and in the presence of added TGF-beta1. Thus, when TGF-beta acts as a co-stimulator for T-cell activation it inhibits the induction of apoptosis and sustains the number of viable cells.

Thymic atrophy caused by thymocyte apoptosis in experimental severe acute pancreatitis

Although a reduction in peripheral lymphocytes has been reported in clinical cases of acute pancreatitis, the thymic change remains still unknown. To investigate impairment of cellular immunity in acute pancreatitis, alterations of the thymus in rats with acute pancreatitis were examined experimentally. Male Wistar rats were used. Two groups with pancreatitis of different severity and a control group for each were established. The thymus was weighed and the number of thymocytes counted. Apoptosis in the thymus was examined by in situ nick-end labeling, DNA agarose gel electrophoresis, and cell cycle analysis using propidium iodide. Both thymus weight and number of thymocytes decreased significantly in the rats with necrotizing pancreatitis 20 h after induction of pancreatitis (P <0.02 vs sham operation). Neither thymus atrophy nor thymocyte reduction was observed in rats with edematous pancreatitis. In thymuses from rats with necrotizing pancreatitis, in situ nick-end labeling showed a significant increase in apoptotic changes of thymocytes, which was also confirmed by the stepladder pattern on agarose gel electrophoresis of the extracted DNA and by cell cycle analysis. It is concluded that thymus atrophy associated with apoptosis occurs in rats with necrotizing pancreatitis.

Gene expression of IL-10 in relationship to TNF-alpha, IL-1beta and IL-2 in the rat brain following middle cerebral artery occlusion

To systematically elucidate the gene expression of inflammatory and immune modulators following middle cerebral artery occlusion (MCAO) in the rat, we studied interleukin-10 (IL-10) along with tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta (IL-1beta) and interleukin-2 (IL-2). Gene expression of these cytokines was studied ipsilateral and contralateral to the MCAO, with mRNA expression levels evaluated 2, 4, 6, 8 and 12 h following permanent MCAO by reverse transcriptase polymerase chain reaction (RT-PCR). In the ischemic hemisphere TNF-alpha and IL-1beta mRNA increased at 2 h following MCAO and peaked at 6 h, with IL-10 mRNA detected only at 6 h. Contralaterally, both TNF-alpha and IL-1beta mRNAs were expressed with a similar pattern to that in the ischemic hemisphere, but at lower levels, with no contralateral IL-10 expression. There was no difference in IL-2 gene expression between control and experimental animals in either hemisphere. These results demonstrate that IL-10 and TNF-alpha, IL-1beta gene expression is induced early following MCAO. The temporal profile of these cytokines is similar to that seen in sepsis, where TNF-alpha induces IL-10; subsequently IL-10 inhibits TNF-alpha expression. The similarity of the temporal profile of cytokine expression in sepsis and cerebral ischemia suggests that IL-10 should be studied as a potential inhibitor of TNF-alpha production in ischemic brain tissue. The factors inducing contralateral expression of the inflammatory cytokines, TNF-alpha and IL-1beta, along with the potential clinical significance of this remote cytokine gene expression, merit further study.

Modulation of apoptosis with cytokines in B-cell chronic lymphocytic leukaemia

In B chronic lymphocytic leukaemia (B-CLL) non-proliferating peripheral blood (PB) B cells have a long life span in vivo. In cultures, these cells die spontaneously by apoptosis. Interleukin (IL) 4 inhibits spontaneous apoptosis (SA) and promotes survival of B-CLL B cells in vitro. No such effect is observed in PB B cells from normal healthy donors. The anti-apoptotic effect of IL4 is independent of mitogen-induced cell activation but depends on the concentration of IL4. The protective effect of IL4 is specific and it is significantly reduced or abolished with anti-IL4 antibody. Interferon (IFN)-gamma and alpha- IFN also protect B-CLL B cells from apoptosis in vitro. Sera from B-CLL patients have increased levels of IFN-gamma when compared with sera from healthy donors. In addition, B-cells in B-CLL express detectable levels of IFN-gamma mRNA. Other cytokines, namely ILl, IL2, IL6 and IL7 do not affect SA of B-CLL B cells. By contrast, IL5 and antibody to apolipoprotein-1 (APO- 1) receptor increase SA significantly and in a dose-dependent manner. Interleukin 4 protects B-CLL B cells from IL5-, anti(alpha) APO-1- and steroid-induced apoptosis. The mode of action of the cytokines inducing apoptosis or protecting B-CLL B cells from dying is largely unknown. Recently the bcl-2 proto-oncogene has been associated with prolonged cell survival. However, the involvement of bel-2 in spontaneous, cytokine-induced or steroid-induced apoptosis in B-CLL has been controversial. Some authors have reported down-regulation of bcl-2 protein expression in B-CLL B-cells undergoing SA or in steroid-treated cells with IL4 preventing this down-regulation. By contrast, others observed no significant loss of bcl-2 protein expression in steroid-, alpha-APO-1 - and IL5-treated cells when compared with untreated or fresh cells. Also, no correlation between bcl-2 protein expression and protection with IL4 has been reported. In conclusion, in B-CLL IL4, IFN-gamma and alpha-IFN promote the survival of the leukaemic cells. These cytokines may therefore be involved in the pathogenesis of the B-CLL.

Programmed cell death in brains of HIV-1-positive AIDS and pre-AIDS patients

Neuropathological studies have revealed that the brains of HIV-1-infected AIDS patients show the typical encephalitis and, in addition, neuronal loss. More recently, this neuronal cell loss has been thought to take place via programmed cell death (apoptosis) which has been demonstrated by an in situ end labelling (ISEL) technique. In this study 54 brains of HIV-1-positive patients were investigated by the ISEL technique to investigate whether apoptosis is also present in the brains of patients at the asymptomatic stage. Of these, 10 patients suffered from HIV encephalitis (HIVE), 8 had AIDS without neuropathological disorders and 36 were HIV-1-positive pre-AIDS patients. Apoptotic cells were detected in 6 of the 10 HIVE, 1 of the 8 AIDS without central nervous system (CNS) disease and 4 of the 36 asymptomatic individuals. A difference seen between the AIDS and pre-AIDS cases was that, in the latter, apoptotic cells were found in the white matter in all 4 cases, while only 2 of these 4 showed apoptotic neurons. The presence of apoptotic cells in a number, albeit small, of brains of HIV-1-positive pre-AIDS individuals, combined with abnormalities described previously in the same group of patients gives further support to the opinion that brain damage already occurs during the early stages of HIV infection.

Induction of apoptotic cell death by pancreatitis-associated ascitic fluid in Madin-Darby canine kidney cells

We investigated the cytotoxicity on Madin-Darby canine kidney (MDCK) cells of pancreatitis-associated ascitic fluid (PAAF) collected from rats with experimental necrotizing pancreatitis. PAAF reduced viability of MDCK cells in a time- and dose-dependent manner. We detected DNA fragmentation on the PAAF-treated MDCK cells, indicating that the cytocidal action of PAAF is via apoptosis. From the results obtained, we conclude that PAAF contains factor(s) inducing apoptosis on MDCK cells, and we assume that apoptotic cell death is involved in the mechanism of organ failure in acute pancreatitis.

Thymus involution induced by mouse hepatitis virus A59 in BALB/c mice

Mouse hepatitis virus A59 (MHV-A59) infection of adult BALB/c mice induced a severe, transient atrophy of the thymus. The effect was maximal at 1 week after infection, and thymuses returned to normal size by 2 weeks after infection. There was no effect of glucocorticoids, since thymus atrophy was also found in adrenalectomized, infected mice. In infected thymus, immature CD4+ CD8+ lymphocytes were selectively depleted, and apoptosis of lymphocytes was increased. The MHV receptor glycoprotein MHVR was detected on thymus epithelial cells but not on T lymphocytes. In a small number of stromal epithelial cells, but in very few lymphocytes, the viral genome was detectable by in situ hybridization. These observations suggested that MHV-A59-induced thymic atrophy results not from a generalized lytic infection of T lymphocytes but rather from apoptosis of immature double-positive T cells that might be caused by infection of a small proportion of thymus epithelial cells or from inappropriate secretion of some factor, such as a cytokine.