Nitric oxide mediates dendritic cell apoptosis by downregulating inhibitors of apoptosis proteins and upregulating effector caspase activity

Anti‑inflammatory mechanism of berberine on lipopolysaccharide‑induced IEC‑18 models based on comparative transcriptomics

Intestinal surface epithelial cells (IECs) have long been considered as an effective barrier for maintaining water and electrolyte balance, and are involved in the mechanism of nutrient absorption. When intestinal inflammation occurs, it is often accompanied by IEC malfunction. Berberine (BBR) is an isoquinoline alkaloid found in numerous types of medicinal plants, which has been clinically used in China to treat symptoms of gastrointestinal pathogenic bacterial infection, especially bacteria‑induced diarrhea and inflammation. In the present study, IEC‑18 rat intestinal epithelial cells were treated with lipopolysaccharide (LPS) to establish an in vitro model of epithelial cell inflammation, and the cells were subsequently treated with BBR in order to elucidate the anti‑inflammatory mechanism. Transcriptome data were then searched to find the differentially expressed genes (DEGs) compared between two of the treatment groups (namely, the LPS and LPS+BBR groups), and DEGs were analyzed using Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, Weighted Gene Correlation Network Analysis and Interactive Pathways Explorer to identify the functions and pathways enriched with DEGs. Finally, reverse transcription‑quantitative PCR was used to verify the transcriptome data. These experiments revealed that, comparing between the LPS and LPS+BBR groups, the functions and pathways enriched in DEGs were 'DNA replication', 'cell cycle', 'apoptosis', 'leukocyte migration' and the 'NF‑κB and AP‑1 pathways'. The results revealed that BBR is able to restrict DNA replication, inhibit the cell cycle and promote apoptosis. It can also inhibit the classic inflammatory pathways, such as those mediated by NF‑κB and AP‑1, and the expression of various chemokines to prevent the migration of leukocytes. According to transcriptomic data, BBR can exert its anti‑inflammatory effects by regulating a variety of cellular physiological activities, including cell cycle, apoptosis, inflammatory pathways and leukocyte migration.

Tumor microenvironment-related dendritic cell deficiency: a target to enhance tumor immunotherapy

Dendritic cells (DCs), as specialized antigen-presenting cells, are essential for the initiation of specific T cell responses in innate antitumor immunity and, in certain cases, support humoral responses to inhibit tumor development. Mounting evidence suggests that the DC system displays a broad spectrum of dysfunctional status in the tumor microenvironment (TME), which ultimately affects antitumor immune responses. DC-based therapy can restore the function of DCs in the TME, thus showing a promising potential in tumor therapy. In this review, we provide an overview of the DC deficiency caused by various factors in the TME and discuss proposed strategies to reverse DC deficiency and the applications of novel combinatorial DC-based therapy for immune normalization of the tumor.

The role of nitric oxide in metabolic regulation of Dendritic cell immune function

Dendritic cells (DCs) are canonical antigen presenting cells of the immune system and serve as a bridge between innate and adaptive immune responses. When DCs are activated by a stimulus through toll-like receptors (TLRs), DCs undergo a process of maturation defined by cytokine & chemokine secretion, co-stimulatory molecule expression, antigen processing and presentation, and the ability to activate T cells. DC maturation is coupled with an increase in biosynthetic demand, which is fulfilled by a TLR-driven upregulation in glycolytic metabolism. Up-regulation of glycolysis in activated DCs provides these cells with molecular building blocks and cellular energy required for DC activation, and inhibition of glycolysis during initial activation impairs both the survival and effector function of activated DCs. Evidence shows that DC glycolytic upregulation is controlled by two distinct pathways, an early burst of glycolysis that is nitric oxide (NO) -independent, and a sustained commitment to glycolysis in NO-producing DC subsets. This review will address the complex role of NO in regulating DC metabolism and effector function.

Immunologic and Hematological Abnormalities in Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a leading cause of mortality in preterm infants. This article reviews the immunologic and hematological abnormalities typically seen in infants with NEC, such as elevated plasma cytokine levels, thrombocytopenia, increased or decreased neutrophil counts, low monocyte counts, and anemia. Some of these findings may provide important diagnostic and prognostic information.

Inflammatory signaling in necrotizing enterocolitis

The pathogenesis of necrotizing enterocolitis (NEC) is complex and its speed of progression is variable. To gain understanding of the disease, researchers have examined tissues resected from patients with NEC; however, as these are obtained at late stages of the disease, they do not yield clues about the early pathogenic events leading to NEC. Therefore, animal models are used and have helped identify a role for several mediators of the inflammatory network in NEC. In this article, we discuss the evidence for the role of these inflammatory mediators and conclude with a current unifying hypothesis regarding NEC pathogenesis.

Nitric oxide controls an inflammatory-like Ly6C(hi)PDCA1+ DC subset that regulates Th1 immune responses

Using NOS2 KO mice, we investigated the hypothesis that NO modulation of BM-DC contributes to the NO-mediated control of Th1 immune responses. BM-DCs from NOS2 KO mice, compared with WT BM-DCs, have enhanced survival and responsiveness to TLR agonists, develop more Ly6C(hi)PDCA1(+) DCs that resemble inflammatory DCs and produce high levels of inflammatory cytokines. Also, compared with WT-infected mice, NOS2 KO mice infected with WNV showed enhanced expansion of a similar inflammatory Ly6C(hi)PDCA1(+) DC subset. Furthermore, in contrast to WT DCs, OVA-loaded NOS2 KO BM-DCs promoted increased IFN-γ production by OTII CD4(+) T cells in vitro and when adoptively transferred in vivo. The addition of a NO donor to NOS2 KO BM-DCs prior to OTII T cells priming in vivo was sufficient to revert Th1 immune responses to levels induced by WT BM-DCs. Thus, autocrine NO effects on maturation of inflammatory DCs and on DC programming of T cells may contribute to the protective role of NO in autoimmune diseases and infections. Regulating NO levels may be a useful tool to shape beneficial immune responses for DC-based immunotherapy.

Microarray analysis of cytokine activation of apoptosis pathways in the thyroid

It has been suggested that Fas-mediated apoptosis plays an important role in the pathogenesis of autoimmune thyroid diseases. Our previous studies have demonstrated that normal primary thyroid epithelial cells are resistant to Fas-mediated apoptosis, but the resistance can be overcome by pretreatment with a combination of interferon-gamma (IFN-gamma) and IL-1beta. To understand the molecular mechanism responsible for the IFN-gamma/IL-1beta effects, we profiled changes in the transcription induced by these two cytokines in normal human thyroid cells, using cDNA microarrays. We found that IFN-gamma/IL-1beta showed a significant increase in apoptosis-related genes such as inducible nitric oxide synthase (iNOS), receptor-interacting protein 2 (RIP2), and caspases 10. These increases were confirmed by other methods, including real-time PCR and Western blot. Furthermore, the sensitization of primary thyroid epithelial cells to Fas-mediated apoptosis by IFN-gamma/IL-1beta was significantly blocked by a general caspase inhibitor, z-VAD, or by the combination of two specific individual caspase inhibitors. In addition, our results showed that IFN-gamma/IL-1beta enhance p38 MAPK phosphorylation and that SB 203580, a p38 MAPK inhibitor, can inhibit IFN-gamma/IL-1beta-induced p38 MAPK phosphorylation. SB 203580 also significantly prevented cytokine-induced iNOS expression and caspase activation and thus blocked Fas-mediated apoptosis of thyroid cells sensitized by IFN-gamma/IL-1beta. In conclusion, our data suggest that both p38 MAPK and iNOS are involved in IFN-gamma/IL-1beta-induced sensitization of the thyroid cells to Fas-mediated apoptosis via the activation of caspases 3, 7, and 10 and that this pathway may be further activated by BID. This hints that inflammatory cytokines regulate death-receptor-mediated apoptosis at multiple points in the process.

Nitric oxide induces apoptosis in cutaneous T cell lymphoma (HuT-78) by downregulating constitutive NF-κB

Constitutive active NF-kappaB have been shown to protect cutaneous T cell lymphoma (CTCL) cells from apoptosis. In the present study, we have studied the cytotoxic potential of nitric oxide generating compound, sodium nitroprusside (SNP) on CTCL cell line, HuT-78. Treatment of cells with SNP resulted in decrease in mitochondrial membrane potential, cytochrome c release, activation of caspase-3 and poly (ADP ribose) polymerase cleavage. SNP treatment inhibited activation of NF-kappaB in a concentration dependent manner. SNP increased the expression of IkappaBalpha without affecting the phosphorylation of IkappaBalpha. Downregulation of NF-kappaB by SNP decreased p65 nuclear translocation as evident by confocal fluorescence microscopy. Further it was found that SNP treatment caused downregulation of Bcl-2 family member (Bcl-xl) in HuT-78 cells. Thus, we have provided evidence that SNP induces apoptosis in CTCL cell line, HuT-78 by downregulating constitutive NF-kappaB and thereby Bcl-xl expression.

Production of nitric oxide and self-nitration of proteins during monocyte differentiation to dendritic cells

Nitric oxide (NO) can stimulate dendritic cells to a more activated state. However, nitric oxide and peroxynitrites production by dendritic cells has been usually associated with pathological situations such as autoimmunity or inflammatory diseases. This study was designed to determine if dendritic cells obtained from healthy volunteers produce nitric oxide and peroxynitrites, which results in protein nitration. The expression of arginase II, but not arginase I, isoform was detected in monocytes and dendritic cells. There was higher inducible nitric oxide synthase (iNOS) protein expression and lower arginase activity both in immature and mature dendritic cells, compared to monocytes. This caused nitric oxide production, and maturation of dendritic cells which provoked a significative increase of nitrites and nitrates compared to immature dendritic cells. There was also peroxynitrites synthesis during monocyte differentiation as shown by the nitration of proteins. Immunoblot revealed a pattern of nitrated proteins in cell extracts obtained from monocytes and dendritic cells, however there were bands that appeared only in human dendritic cells, in particular an intense 90 kDa band. Nitric oxide production and nitrotyrosine formation could affect the antigen presentation and modify the immune response.

Expression of inducible nitric oxide synthase is significantly correlated with expression of vascular endothelial growth factor and dendritic cell infiltration in patients with advanced gastric carcinoma

OBJECTIVE

Nitric oxide (NO) is a product of L-arginine to L-citrulline conversion by nitric oxide synthase (NOS). The inducible form of NOS (iNOS) is one of three classes of NOS and the strongest producer of NO. It has been reported that NO correlates with angiogenesis and immune responses in some types of cancer, however, the correlations between iNOS expression, angiogenesis, and immune responses are still unclear in gastric carcinoma.

METHODS

iNOS expression was determined in 135 gastric cancer patients by immunohistochemical procedures and compared with the expression of vascular endothelial growth factor (VEGF), microvessel (MV) density, and dendritic cell (DC) infiltration to evaluate the effect of iNOS on angiogenesis and immune responses in gastric carcinoma.

RESULTS

iNOS expression was detected in 106 (78.5%) of 135 cases. There was a close correlation between iNOS expression and VEGF expression, a correlation with MV density and an inverse correlation with DC infiltration. There was no correlation between iNOS and p53 expression. The prognoses of patients whose tumors expressed iNOS were significantly worse than those of patients whose tumors did not express iNOS. Multivariate analysis indicated iNOS expression was an independent prognostic factor.

CONCLUSION

iNOS might be associated with tumor progression by stimulating angiogenesis and suppressing immune responses in gastric carcinoma.

Analysis of the activation profile of dendritic cells derived from the bone marrow of interleukin-12/interleukin-23-deficient mice

We have previously shown that macrophages from interleukin (IL)-12p40 gene knockout (IL-12/IL-23-/-) mice have a bias towards the M2 activation profile, spontaneously secreting large quantities of transforming growth factor-beta1 (TGF-beta1) and producing low levels of nitric oxide (NO) in response to lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma). To verify whether the activation profile of dendritic cells (DCs) is also influenced by the absence of IL-12/IL-23, bone marrow-derived DCs from IL-12/IL-23-/- and C57BL/6 mice were evaluated. At first we noticed that approximately 50% of the C57BL/6 DCs were dead after LPS-induced maturation, whereas the mortality of IL-12/IL-23-/- DCs was < 10%, a protective effect that diminished when recombinant IL-12 (rIL-12) was added during maturation. Similarly to macrophages, mature IL-12/IL-23-/- DCs (mDCs) produced higher levels of TGF-beta1 and lower levels of NO than C57BL/6 mDCs. NO release was IFN-gamma-dependent, as evidenced by the poor response of IFN-gamma-/- and IL-12/IL-23-/-IFN-gamma-/- mDCs. Nevertheless, IFN-gamma deficiency was not the sole reason for the weak NO response observed in the absence of IL-12/IL-23. The high level of TGF-beta1 secretion by IL-12/IL-23-/- mDCs could explain why exogenous IFN-gamma partially restored the NO production of IFN-gamma-/- mDCs, while IL-12/IL-23-/- IFN-gamma-/- mDCs remained unresponsive. We also showed that CD4+ T-cell proliferation was inhibited by C57BL/6 mDCs, but not by IL-12/IL-23-/- mDCs. IFN-gamma and NO appear to mediate this antiproliferative effect because this effect was not observed in the presence of mDCs from IFN-gamma-/- or IL-12/IL-23-/- IFN-gamma-/- mice and it was attenuated by aminoguanidine. We conclude that the presence of IL-12/IL-23 during LPS-induced maturation influences the activation profile of DCs by a mechanism that is, only in part, IFN-gamma dependent.

The intimate relation between nitric oxide and superoxide in apoptosis and cell survival

Intra- and intercellular communication in or between cells allows adaptation to changes in the environment. Formation of reactive oxygen (ROS) and nitrogen (RNS) species in response to external insults gained considerable attention in provoking cell demise along an apoptotic subroute of cell death, thus attributing radical formation to pathologies. In close association, stabilization of the tumor suppressor p53 and activation of caspases convey proapoptotic signaling. Complexity was added with the notion that ROS and RNS signals overlap and/or produce synergistic as well as antagonistic effects. With respect to nitric oxide (NO) signaling, it became clear that the molecule is endowed with pro- or antiapoptotic signaling capabilities, depending to some extend on the concentration and cellular context, i.e., ROS generation. Here, some established concepts are summarized that allow an explanation of p53 accumulation under the impact of NO and an understanding of NO-evoked cell protection at the level of caspase inhibition, cyclic GMP formation, or expression of antiapoptotic proteins. In addition, the overlapping sphere of ROS and RNS signaling is recapitulated to appreciate cell physiology/pathology with the notion that marginal changes in the flux rates of either NO or superoxide may shift vital signals used for communication and cell survival into areas of pathology in close association with apoptosis/necrosis.

Effect of nitric oxide in the differentiation of human monocytes to dendritic cells

The aim of this work was to study the influence of nitric oxide (NO) in the differentiation of human monocytes to dendritic cells. Human monocytes from healthy donors were differentiated to immature dendritic cells in presence of GM-CSF and IL-4. Maturation of dendritic cells was achieved with GM-CSF and TNF-alpha. Nitric oxide donors (SIN-1, DEA-NO or DETA-NO) were added during differentiation of monocytes to dendritic cells and also during dendritic cells maturation. Immature dendritic cells showed a characteristic phenotype CD80+ CD1a+ HLA-DR+ CD86+ CD40+ CD14(low/-), different from adherent monocytes CD80- CD1a- HLA-DR+ CD86+ CD40- CD14++. The addition of SIN-1 the first day of monocyte differentiation reduced cell viability and increased the percentage of apoptotic immature dendritic cells. Peroxynitrite donor, SIN-1, produced more toxic effects than DEA-NO or DETA-NO. An increase in the subpopulation CD1a+ CD80+ HLADR+ of immature dendritic cells was observed when SIN-1 or DEA-NO, but not DETA-NO, was added at the beginning of monocyte culture. There was a significant reduction in the expression of TNF-alpha receptor of mature dendritic cells when SIN-1 and DEA-NO were added together GM-CSF and TNF-alpha at the beginning of maturation. The presence of SIN-1, DEA-NO or DETA-NO in maturation induced an increase of CD83+ cells. These results suggest that nitric oxide affects differentiation and maturation of dendritic cells and this effect depends on the nitric oxide donor used.

Nitric oxide-modulated marker gene expression of signal transduction pathways in lung endothelial cells

Nitric oxide (NO) is a signal molecule involved in regulation of physiological and pathophysiological functions of the vascular endothelium such as apoptosis. We examined whether NO-modulates marker gene expression of signal transduction pathways in cultured pulmonary artery endothelial cell (PAEC). Cells were exposed to a NO donor, 1 mM NOC-18, for 0.5, 5, and 24 h, thereafter, expression levels of 96 marker genes associated with 18 signal transduction pathways were assessed using a signal transduction pathway-finder microarray analysis system. NO modulation of apoptotic pathways and nuclear factor (NF) microarray were further analyzed. Gene array analyses revealed that 17 genes in 13 signal pathways were up- or down-regulated in cells exposed to NO, four of which were significantly altered by NO and are associated with apoptotic pathways. Apoptotic pathways resulted in identification of 11 genes in this group. Nuclear factor microarray studies demonstrated that NO-modulated expression of these signal transduction genes was associated with regulation of NF-binding activities. Gel shift analysis verified the effects of NO on DNA-binding activity of NF. These results demonstrated that NO signaling modulates at least 13 signal transduction pathways including apoptosis-related families in PAEC.

Function and survival of dendritic cells depend on endothelin-1 and endothelin receptor autocrine loops

The biologic effects of endothelin-1 (ET-1) are not limited to its potent vasoconstricting activity. The endothelin receptors, ETA and ETB, have differential tissue and functional distributions. Here we showed that dendritic cells (DCs), the major antigen-presenting cells in the adaptive limb of the immune system, produce large amounts of ET-1 and significantly increase the expression of endothelin receptors upon maturation. Selective blockade of the ETA receptor significantly reduced expression of the mature DC marker CD83, decreased the production of the immunostimulatory cytokine interleukin-12, down-regulated DC ability to stimulate T cells, and promoted DC apoptosis. Selective ETB receptor blockade, on the other hand, resulted in increased expression of CD83 and improved DC survival. Therefore, ET-1/ETA/ETB autocrine/paracrine loops on DCs appear to be essential for the normal maturation and function of human DCs, presenting a unique target for immunomodulatory therapies.

Nitric oxide-mediated inhibition of caspase-dependent T lymphocyte proliferation

Nitric oxide (NO), a pleiotropic signaling molecule produced at sites of inflammation, is a powerful inhibitor of lymphocyte proliferation. Caspases, central effector proteases in apoptosis, have recently been implicated as critical mediators of T cell activation. We and others have shown that NO can inhibit caspases by S-nitrosylation, which is reversible by the reducing agent dithiothreitol (DTT). The purpose of the present study was to determine whether NO inhibits lymphocyte proliferation by modulating caspase activity. Caspase inhibition with z-VAD-fmk blocked T cell proliferation. NO-dependent inhibition of T cell proliferation was associated with an inhibition of caspase activity and activation, and this effect was reversible by DTT. Previous studies demonstrated inhibition of apoptosis through S-nitrosylation of caspases; the present studies extend this effect to inhibition of caspase-dependent T cell proliferation.

Nitric oxide-related toxicity in cultured astrocytes: effect of Bacopa monniera

There is growing evidence that high concentrations of nitric oxide (NO), generated by activated astrocytes, might be involved in a variety of neurodegenerative diseases, such as Alzheimer's disease, ischemia and epilepsy. It has recently been suggested that glial cells may produce NO under superoxide radical stimulation by enzyme-independent mechanism. This suggests that also natural antioxidants may have therapeutical relevance in neurodegenerative diseases. Studies of Bhattacharya et al. have evidenced that Bacopa monniera (BM) (family Scrophulariaceae), an Ayurvedic medicinal plant clinically used for memory enhancing, epilepsy, insomnia and as a mild sedative, is able to reduce the memory-dysfunction in rat models of Alzheimer's disease, but the molecular mechanisms of this action are yet to be determined. In the present study, we examined the effect of a methanolic extract of BM on toxicity induced by the nitric oxide donor, S-nitroso-N-acetyl-penicillamine (SNAP), in culture of purified rat astrocytes. Our results indicate that, after 18 h of treatment, SNAP induced an increase in the production of reactive species, but did not induce the rupture of cellular membrane. Conversely, this NO donor induced a fragmentation of genomic DNA compared to control astrocytes. The extract of BM inhibited the formation of reactive species and DNA damage in a dose dependent manner. This data supports the traditional use of BM and indicates that this medicinal plant has a therapeutic potential in treatment or prevention of neurological diseases.

Mechanism of intestinal-derived fungal sepsis by gliotoxin, a fungal metabolite

BACKGROUND/PURPOSE

Gut barrier dysfunction resulting from fungal overgrowth may be caused by the interaction of gliotoxin (GT), a fungal metabolite, with enterocytes. The goal of this study was to determine the mechanisms by which gliotoxin (GT), a fungal metabolite, causes enterocyte apoptosis.

METHODS

The authors measured enterocyte apoptosis, caspase-3 activity, pro-caspase-3, and poly (ADP-ribose) polymerase (PARP) cleavage in GT-exposed IEC-6 cells, a rat intestinal cell line.

RESULTS

GT induced apoptosis in IEC-6 cells. The pan-caspase inhibitor ZVAD suppressed this GT-mediated apoptosis. GT induced a 15-fold increase in caspase-3 activity over media control. The authors detected PARP cleavage by after GT exposure. DTT pretreatment decreased apoptosis compared with GT alone.

CONCLUSIONS

This study supports the concept that fungal overgrowth may lead to gut barrier dysfunction by the local release of gliotoxin and the induction enterocyte apoptosis.

Mechanisms of sodium nitroprusside-induced death in human chondrocytes

The nitric oxide (NO) donor sodium nitroprusside (SNP) has been used to study NO-dependent cell death in human chondrocytes. This study compares SNP-induced chondrocyte death and SNP-activated signaling mechanisms with apoptosis induced by CD95 activation. Sodium nitroprusside increased cell death dose-dependently. Compared to CD95 stimulation, SNP induced only low levels of internucleosomal DNA fragmentation as measured by cell-death enzyme-linked immunosorbent assay (ELISA). However, SNP caused substantial nuclear DNA cleavage, as evidenced by terminal deoxynucleotidyltransferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick end-labeling (TUNEL). Caspase-3 processing in response to SNP was not detected. The pancaspase inhibitor Z-VAD.FMK partially abrogated the TUNEL signal but did not block cell death or internucleosomal DNA fragmentation. The caspase-3-specific inhibitor Ac-DEVD-CHO did not inhibit the SNP-induced TUNEL signal or internucleosomal DNA fragmentation. DNA degradation was not blocked by the p38 inhibitor SB 202190 but by the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine. The results of this study support the hypothesis that the phenotype and mechanisms of SNP-induced chondrocyte death are distinct from apoptosis induction via CD95.