The role of prostaglandin E2 and nitric oxide in cell death in J774 murine macrophages

In Vitro Anti-Inflammatory Effects of Symplocos sumuntia Buch.-Ham. Ex D. Don Extract via Blockage of the NF-κB/JNK Signaling Pathways in LPS-Activated Microglial Cells

Symplocos sumuntia Buch.-Ham. ex D. Don (S. sumuntia) is a traditional medicinal herb used in Asia to treat various pathologies, including cough, stomachache, tonsillitis, hypertension, and hyperlipidemia. Although the anti-inflammatory activity of S. sumuntia has been reported, little is known about its anti-inflammatory activity and molecular mechanisms in microglial cells. Therefore, we investigated the inhibitory effects of S. sumuntia methanol extract (SSME) on the inflammatory responses in lipopolysaccharide (LPS)-treated BV2 cells. The SSME significantly inhibited the LPS-stimulated inducible nitric oxide synthase and cyclooxygenase-2 expression, as well as the production of nitric oxide (NO), a proinflammatory mediator. The production of proinflammatory cytokines, including interleukin (IL)-6, tumor necrosis factor-α, and IL-1β, was suppressed by the SSME in the LPS-induced BV2 cells. The mechanism underlying the anti-inflammatory effects of SSME involves the suppression of the LPS-stimulated phosphorylation of mitogen-activated protein kinases (MAPKs) such as JNK. Moreover, we showed that the LPS-stimulated nuclear translocation of the nuclear factor-κB (NF-κB)/p65 protein, followed by IκB degradation, was decreased by the SSME treatment. Collectively, these results showed that the SSME induced anti-inflammatory effects via the suppression of the MAPK signaling pathways, accompanied by changes in the NF-κB translocation into the nucleus. Therefore, SSME may be employed as a potential therapeutic candidate for various inflammatory diseases.

Triptolide Modulates the Expression of Inflammation-Associated lncRNA-PACER and lincRNA-p21 in Mycobacterium tuberculosis-Infected Monocyte-Derived Macrophages

Triptolide is a diterpene triepoxide, which performs its biological activities via mechanisms including induction of apoptosis, targeting of pro-inflammatory cytokines, and reshaping of the epigenetic landscape of target cells. However, the targeting of long non-coding RNAs (lncRNAs) by triptolide has not yet been investigated, despite their emerging roles as key epigenetic regulators of inflammation and immune cell function during Mycobacterium tuberculosis (Mtb) infection. Hence, we investigated whether triptolide targets inflammation-associated lncRNA-PACER and lincRNA-p21 and how this targeting associates with Mtb killing within monocyte-derived macrophages (MDMs).Using RT-qPCR, we found that triptolide induced the expression of lincRNA-p21 but inhibited the expression of lncRNA-PACER in resting MDMs in a dose- and time-dependent manner. Moreover, Mtb infection induced the expression of lincRNA-p21 and lncRNA-PACER, and exposure to triptolide before or after Mtb infection led to further increase of Mtb-induced expression of these lncRNAs in MDMs. We further found that contrary to lncRNA-PACER, triptolide time- and dose-dependently upregulated Ptgs-2, which is a proximal gene regulated by lncRNA-PACER. Also, low-concentration triptolide inhibited the expression of cytokine IL-6, a known target of lincRNA-p21. Mtb infection induced the expression of IL-6 and Ptgs-2, and triptolide treatment further increased IL-6 but decreased Ptgs-2 expression in Mtb-infected MDMs. The inverse relation between the expression of these lncRNAs and their target genes is concordant with the conception that these lncRNAs mediate, at least partially, the cytotoxic and/or anti-inflammatory activities of triptolide in both resting and activated MDMs. Using the CFU count method, we found that triptolide decreased the intracellular growth of Mtb HN878. The alamarBlue assay showed that this decreased Mtb HN878 growth was not as a result of direct targeting of Mtb HN878 by triptolide, but rather evoking MDMs’ intracellular killing mechanisms which we speculate could include triptolide-induced enhancement of MDMs’ effector killing functions mediated by lncRNA-PACER and lincRNA-p21. Altogether, these results provide proof of the modulation of lncRNA-PACER and lincRNA-p21 expression by triptolide, and a possible link between these lncRNAs, the enhancement of MDMs’ effector killing functions and the intracellular Mtb-killing activities of triptolide. These findings prompt for further investigation of the precise contribution of these lncRNAs to triptolide-induced activities in MDMs.

Andrographolide acts as an anti-inflammatory agent in LPS-stimulated RAW264.7 macrophages by inhibiting STAT3-mediated suppression of the NF-κB pathway

ETHNOPHARMACOLOGICAL SIGNIFICANCE

Inflammation is involved in numerous diseases, such as chronic inflammatory disease and cancer. Many plant products exhibit useful biological activities, including antifungal, antibacterial, and anti-inflammatory actions.

AIM OF STUDY

However, our understanding of the anti-inflammatory effects of andrographolide is limited.

MATERIALS AND METHODS

We use lipopolysaccharide (LPS)-stimulated macrophages as a model of inflammation to investigate the anti-inflammatory effects of andrographolide, which contains polyphenolic structures.

RESULTS

We found that andrographolide exhibited a potent anti-inflammatory effect. In this study, we investigated the inhibitory effects of andrographolide on the induction of nitric oxide synthase (NOS) and cyclooxygenase-2 (COX-2) as well as their respective downstream products, NO and PGE2, in RAW264.7 cells treated with LPS. Treatment with andrographolide also reduced nuclear factor-κB (NF-κB) and activation protein-1 (AP-1) DNA-binding activity. Western blot analysis showed that andrographolide significantly inhibited the phosphorylation of signal transducer and activator of transcription-3 (STAT3) and the protein expression of CCAAT/enhancer-binding protein δ (C/EBPδ). We also found that andrographolide suppressed LPS-induced suppressor of cytokine signalling 1 and 3 (SOCS1 and 3) mRNA expression, which, in turn, inhibited apoptosis signalling and mitochondria membrane potential activation. Our results demonstrate that andrographolide downregulates inflammatory iNOS and COX-2 gene expression by inhibiting the activation of NF-κB and STAT3 by interfering with the expression of SOCS1 and SOCS3 signalling.

CONCLUSION

Therefore, andrographolide exerts a potent anti-inflammatory effect and could potentially be developed as a useful agent for the chemoprevention of cancer or inflammatory diseases.

Lipid mediators in innate immunity against tuberculosis: opposing roles of PGE2 and LXA4 in the induction of macrophage death

Virulent Mycobacterium tuberculosis (Mtb) induces a maladaptive cytolytic death modality, necrosis, which is advantageous for the pathogen. We report that necrosis of macrophages infected with the virulent Mtb strains H37Rv and Erdmann depends on predominant LXA(4) production that is part of the antiinflammatory and inflammation-resolving action induced by Mtb. Infection of macrophages with the avirulent H37Ra triggers production of high levels of the prostanoid PGE(2), which promotes protection against mitochondrial inner membrane perturbation and necrosis. In contrast to H37Ra infection, PGE(2) production is significantly reduced in H37Rv-infected macrophages. PGE(2) acts by engaging the PGE(2) receptor EP2, which induces cyclic AMP production and protein kinase A activation. To verify a role for PGE(2) in control of bacterial growth, we show that infection of prostaglandin E synthase (PGES)(-/-) macrophages in vitro with H37Rv resulted in significantly higher bacterial burden compared with wild-type macrophages. More importantly, PGES(-/-) mice harbor significantly higher Mtb lung burden 5 wk after low-dose aerosol infection with virulent Mtb. These in vitro and in vivo data indicate that PGE(2) plays a critical role in inhibition of Mtb replication.

Role of mitogen-activated protein kinase cascades in inducible nitric oxide synthase expression by lipopolysaccharide in a rat Schwann cell line

It is well known that the mitogen-activated protein kinase (MAPK) signal transduction pathways is involved in the regulation of inducible nitric oxide synthase (iNOS) in many cellular systems. However, sufficient information describing the role of MAPKs on iNOS expression in rat Schwann cells (SCs) is lacking. Therefore the paper was sought to investigate the role of MAPK cascades in iNOS expression following treatment of lipopolysaccharide (LPS) in a rat Schwann cell line RSC 96. Reverse transcriptase-PCR analysis (RT-PCR) and immunocytochemical staining were performed to detect iNOS expression following LPS induction. Next RT-PCR and Western blot analysis were employed to study expression of iNOS after using inhibitors selective for ERK (PD98059), JNK/SAPK (SP600125) and p38 (SB202190). The production of nitric oxide (NO) was measured by nitrate reductase method. LPS could significantly induce the expression of iNOS located in the cytoplasm in RSC 96 with a concentration- and time-dependent manner. Administration of inhibitors individually and combinations of the three inhibitors at micromolar concentrations suppressed the expression of iNOS and the production of NO. Based on these observations, it is proposed that LPS may activate the rat Schwann cell line RSC 96 to express iNOS and release NO via the MAPK signal transduction pathways.

Class A scavenger receptor-mediated macrophage adhesion requires coupling of calcium-independent phospholipase A(2) and 12/15-lipoxygenase to Rac and Cdc42 activation

Class A scavenger receptors (SR-A) participate in multiple macrophage functions including adhesion to modified extracellular matrix proteins present in various inflammatory disorders such as atherosclerosis and diabetes. By mediating macrophage adhesion to modified proteins and increasing macrophage retention, SR-A may contribute to the inflammatory process. Eicosanoids produced after phospholipase A(2) (PLA(2))-catalyzed release of arachidonic acid (AA) are important regulators of macrophage function and inflammatory responses. The potential roles of AA release and metabolism in SR-A-mediated macrophage adhesion were determined using macrophages adherent to modified protein. SR-A-dependent macrophage adhesion was abolished by selectively inhibiting calcium-independent PLA(2) (iPLA(2)) activity and absent in macrophages isolated from iPLA(2) beta(-/-) mice. Our results further demonstrate that 12/15-lipoxygenase (12/15-LOX)-derived, but not cyclooxygenase- or cytochrome P450-dependent epoxygenase-derived AA metabolites, are specifically required for SR-A-dependent adhesion. Because of their role in regulating actin polymerization and cell adhesion, Rac and Cdc42 activation were also examined and shown to be increased via an iPLA(2)- and LOX-dependent pathway. Together, our results identify a novel role for iPLA(2)-catalyzed AA release and its metabolism by 12/15-LOX in coupling SR-A-mediated macrophage adhesion to Rac and Cdc42 activation.

Aldose reductase mediates endotoxin-induced production of nitric oxide and cytotoxicity in murine macrophages

Aldose reductase (AR) is a ubiquitously expressed protein with pleiotrophic roles as an efficient catalyst for the reduction of toxic lipid aldehydes and mediator of hyperglycemia, cytokine, and growth factor-induced redox-sensitive signals that cause secondary diabetic complications. Although AR inhibition has been shown to be protective against oxidative stress signals, the role of AR in regulating nitric oxide (NO) synthesis and NO-mediated apoptosis has not been elucidated to date. We therefore investigated the role of AR in regulating lipopolysaccharide (LPS)-induced NO synthesis and apoptosis in RAW 264.7 macrophages. Inhibition or RNA interference ablation of AR suppressed LPS-stimulated production of NO and overexpression of iNOS mRNA. Inhibition or ablation of AR also prevented the LPS-induced apoptosis, cell cycle arrest, activation of caspase-3, p38-MAPK, JNK, NF-kappaB, and AP1. In addition, AR inhibition prevented the LPS-induced down-regulation of Bcl-xl and up-regulation of Bax and Bak in macrophages. L-Arginine increased and L-NAME decreased the severity of cell death caused by LPS and AR inhibitors prevented it. Furthermore, inhibition of AR prevents cell death caused by HNE and GS-HNE, but not GS-DHN. Our findings for the first time suggest that AR-catalyzed lipid aldehyde-glutathione conjugates regulate the LPS-induced production of inflammatory marker NO and cytotoxicity in RAW 264.7 cells. Inhibition or ablation of AR activity may be a potential therapeutic target in endotoximia and other inflammatory diseases.

Expression of COX-2 and hsp72 in peritoneal macrophages after an acute ochratoxin A treatment in mice

Ochratoxin A (OTA) is a secondary fungal metabolite produced by Aspergillus and Penicillium strains that elicits a broad spectrum of toxicological effects in animals and man. A single oral OTA administration (10 mg/kg) in mice induced after 24 h oxidative damage and polymorphonuclear leukocyte (PMN) infiltration in parenchymal organs. In fact, OTA treatment increased lipid peroxidation (via malondialdehyde formation) in kidney and liver and PMN accumulation in duodenum, as shown by myeloperoxidase activity. Following in vivo OTA treatment an increase of cyclooxygenase-2 and of heat shock protein 72 expression was evidenced in peritoneal macrophage lysates by Western blot. That OTA modulates these proteins involved in the inflammatory process indicates that the mycotoxin is able to activate immune cells. This study suggests that the oxidative stress, the neutrophil accumulation in parenchymal tissues and the modulation of inflammatory parameters in peritoneal macrophages induced by OTA are involved in its toxicity, and represent early events related to several aspects of OTA mycotoxicosis.

Modulation of macrophage nitric oxide production by prostaglandin D2

BACKGROUND

Nitric oxide and prostaglandins readily become activated in response to inflammatory events. The overproduction of nitric oxide is detrimental to the host. The present study was conducted to examine whether prostaglandin D(2) (PGD(2)) modulates nitric oxide production in macrophages in response to an inflammatory stimulus.

METHODS

Cultures of RAW 264.7 murine macrophages were exposed to Escherichia coli lipopolysaccharide (LPS, 0.01 and 1.0 microg/ml) before and after exposure to PGD(2) (0.01 to 10 nmol). After 24-h incubation, supernatants were collected and nitrite was quantitated by Greiss reaction as a measure of nitric oxide synthesis. Inducible nitric oxide synthase (iNOS) protein was measured by Western blot analysis.

RESULTS

Macrophages exposed to 0.01 and 1.0 microg/ml LPS produced 8.3 +/- 0.2 and 15.0 +/- 1.4 nmol/1.1 x 10(6) cells/24 h of nitrite, respectively. The simultaneous addition of PGD(2) with LPS inhibited nitrite production in a dose-dependent fashion and suppressed iNOS protein expression. A strong time effect was also exhibited when macrophages were incubated with PGD(2) 1 hour before as compared to 7 hours after the addition of LPS (0.01 or 1.0 microg/ml), indicating that the earlier the time PGD(2) was added to the culture media, the greater the inhibition. Prostaglandin D(2) had the capacity to block nitrite synthesis even when added as much as 7 hours after an LPS challenge. Blocking endogenous prostaglandins, using indomethacin (10 microM), suppressed nitrite production.

CONCLUSION

Exogenous PGD(2) caused dose- and time-dependent decreases in LPS-stimulated nitrite production by RAW 264.7 macrophages by hindering iNOS protein expression. Conversely, the endogenous prostaglandins released by these same cells in response to an LPS challenge stimulated nitrite production, which may consequently dampen the inhibitory actions of exogenous PGD(2).

Nitric oxide induces apoptosis via AP-1-driven upregulation of COX-2 in rat pheochromocytoma cells

Cyclooxygenase-2 (COX-2), the rate-limiting enzyme in prostaglandin synthesis, is induced in many cells by numerous inflammatory mediators, including nitric oxide (NO). Upregulation of COX-2 expression has been implicated in the pathophysiology of neuronal cell death. In the present study, we have found that the NO-induced upregulation of COX-2 via activation of activator protein-1 (AP-1) signaling leads to apoptotic cell death. Cultured rat pheochromocytoma (PC12) cells treated with sodium nitroprusside (SNP), a NO-releasing compound, exhibited marked induction of COX-2 expression, which was associated with apoptotic cell death as evidenced by internucleosomal DNA fragmentation, cleavage of poly(ADP-ribose) polymerase, activation of caspase-3, accumulation of p53, increased Bax/Bcl-XL ratio, and dissipation of mitochondrial membrane potential. In addition to the upregulation of COX-2 expression, SNP treatment led to activation of AP-1. Pretreatment of PC12 cells with c-fos antisense oligonucleotide abolished the NO-induced increase in DNA binding of AP-1 and upregulation of COX-2 expression. Furthermore, pretreatment with a selective COX-2 inhibitor (SC58635) rescued the PC12 cells from the apoptotic cell death induced by NO. Similar results were obtained when the NO-induced upregulation of COX-2 expression was blocked by the siRNA interference. These results suggest that excessive NO production during inflammation induces apoptosis in PC12 cells through AP-1-mediated upregulation of COX-2 expression.

Down-modulation of nitric oxide production in murine macrophages treated with crude plant extracts from the Brazilian Cerrado

Several plant species from the Cerrado biome in Brazil are popularly used as herbal medicines for its reputed analgesic, anti-acid, anti-microbial, anti-inflammatory and anti-tumoral properties, among others. It has been reported that some plant extracts interfere in the production of nitric oxide (NO), an important inflammatory mediator. In the present study, we investigated the effect of hexanic and ethanolic extracts from three plant species on NO production by LPS/IFN-gamma-activated J774 macrophages based on traditional use. The cytotoxic effect of the crude extracts was determined by the thiazolyl blue test (MTT) to measure cell viability. Serjania lethalis stem extracts and Cupania vernalis leaf extracts significantly inhibited NO production, while extracts from Casearia sylvestris var. lingua were inactive or showed low activity on NO production, or were very cytotoxic. The ethanolic stem bark and leaf extracts of Serjania lethalis and Cupania vernalis, respectively, almost completely inhibited the production of NO by J774 macrophages. It can be concluded that the selected extracts are potential sources of active compounds that might be used as anti-inflammatory agents.

Bilirubin inhibits iNOS expression and NO production in response to endotoxin in rats

The inducible isoform of heme oxygenase (HO), HO-1, has been shown to play an important role in attenuating tissue injury. Because HO-1 catalyzes the rate-limiting step in bilirubin synthesis, we examined the hypothesis that bilirubin is a key mediator of HO-1 cytoprotection, employing a rat model of endotoxemia. Bilirubin treatment resulted in improved survival and attenuated liver injury in response to lipopolysaccharide infusion. Serum levels of NO and tumor necrosis factor alpha, key mediators of endotoxemia, and hepatic inducible nitric oxide synthase (iNOS) expression were significantly lower in bilirubin-treated rodents versus control animals. Both intraperitoneal and local administration of bilirubin also was found to ameliorate hindpaw inflammation induced by the injection of lambda-carrageenan. Consistent with in vivo results, bilirubin significantly inhibited iNOS expression and suppressed NO production in lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophages. In contrast, bilirubin treatment induced a threefold increase in LPS-mediated prostaglandin synthesis in the absence of significant changes in cyclooxygenase expression or activity, suggesting that bilirubin enhances substrate availability for eicosanoid synthesis. Bilirubin had no effect on LPS-mediated activation of nuclear factor kappaB or p38 mitogen-activated protein kinase, consistent with a nuclear factor kappaB-independent mechanism of action. Taken together, these data support a cytoprotective role for bilirubin that is mediated, at least in part, through the inhibition of iNOS expression and, potentially, through stimulation of local prostaglandin E2 production. In conclusion, our findings suggest a role for bilirubin in mollifying tissue injury in response to inflammatory stimuli and support the possibility that the phenomenon of "jaundice of sepsis" represents an adaptive physiological response to endotoxemia. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).

Studies on the mechanism of caffeine action in alveolar macrophages: caffeine elevates cyclic adenosine monophosphate level and prostaglandin synthesis

We have previously reported that the effects of caffeine on alveolar macrophages are dose-dependent; thus, at low concentrations caffeine prevents apoptosis and at moderate concentrations, the cells proceed into apoptosis. In the current study, the mechanism of caffeine action via prostaglandin synthesis and cyclic adenosine monophosphate (cAMP) was investigated using moderate concentrations of caffeine. The results show that the combination of caffeine with indomethacin, an inhibitor of prostaglandin synthesis, mediated caffeine's effect by increasing cellular viability and lowering superoxide anion production and DNA fragmentation. However, addition of exogenous prostaglandin E2 (PGE2) to the culture in the presence of caffeine had the opposite effect, in which the viability was decreased and anion superoxide production was increased. Incubation of macrophages with exogenous dibutyryl cAMP showed nearly similar effects to caffeine. At low concentrations (<50 micromol/L), higher viability and lower superoxide production pattern were evident and at higher concentrations (>50 micromol/L) the cells proceeded into apoptosis. Therefore, it is suggested that caffeine exerts its effects on macrophages by altering cAMP level and prostaglandin synthesis.

Effect of Non-Steroidal Anti-Inflammatory Drugs on Amyloid-β Formation and Macrophage Activation after Platelet Phagocytosis

Recently, we showed that platelet phagocytosis occurs in human atherosclerotic plaques and leads to foam cell formation. Platelet phagocytosis, resulting in macrophage activation and iNOS induction, was associated with the formation of amyloid-beta peptide (Abeta) via proteolytic cleavage of platelet-derived amyloid precursor protein (APP), possibly by secretases. To test the involvement of gamma-secretase in this process, we used indomethacin, ibuprofen, and sulindac sulfide, non-steroidal anti-inflammatory drugs (NSAIDs) known to alter the gamma-secretase cleaving site of APP, on their ability to inhibit macrophage activation evoked by platelet phagocytosis. J774 macrophages were incubated with human platelets or lipopolysaccharide (LPS) with or without NSAIDs. Nitrite was quantified as a measure for inducible nitric oxide synthase (iNOS) activity. Indomethacin, ibuprofen, sulindac sulfide, and meloxicam concentration-dependently reduced nitrite production by macrophages incubated with platelets, but did not alter LPS-induced iNOS activity or platelet uptake. However, acetylsalicylic acid and naproxen, two NSAIDs without effect on the gamma-secretase cleaving site of APP, did not affect nitrite production in either platelet- or LPS-stimulated macrophages. Surface-enhanced laser desorption/ionization time-of-flight mass-spectrometry demonstrated time-dependent formation of Abeta-containing peptides after platelet phagocytosis, which could be inhibited by indomethacin. In conclusion, these results point to the involvement of gamma-secretase in macrophage activation following platelet phagocytosis.

Cyclooxygenase 2 in infiltrating inflammatory cells in injured nerve is universally up-regulated following various types of peripheral nerve injury

We previously reported the up-regulation of cyclooxygenase 2 (COX2) in injured sciatic nerve of rats with partial sciatic nerve ligation (PSNL) and the reversal of PSNL-elicited tactile allodynia by local injection of the COX inhibitor ketorolac [Eur J Neurosci 15 (2002) 1037]. We further asked whether COX2 up-regulation in injured nerve is a universal phenomenon following various types of nerve injury. In the current study, we observed that abundant COX2 immunoreactive (IR) cell profiles appeared in injured nerves of rats following spinal nerve ligation (SNL), chronic constriction injury (CCI) and complete sciatic nerve transection. Most COX2-IR cells were identified as infiltrating macrophages. Partial injury induced greater COX2 up-regulation than complete injury. COX2 up-regulation reached a peak at 2-4 weeks, evidently declined by 3 months and disappeared by 7 months postlesion. These findings suggest that up-regulation of COX2 in injured nerve is a common event during the initial several months after nerve injury. We observed that local ketorolac-elicited anti-allodynia was closely associated with the abundance of COX2-IR cells in injured nerve, varying with the type of injury and time after injury. The anti-allodynia lasted the longest when local ketorolac was given 2-4 weeks after PSNL, CCI and SNL. The duration of local ketorolac's anti-allodynia was the longest in CCI rats, which also exhibited the most abundant COX2 up-regulation. Local ketorolac's anti-allodynia lasted much shorter when given 2-3 months after lesion. Local ketorolac failed to induce anti-allodynia 7 months after lesion, a time when COX2-IR cells completely disappeared from the injured nerve except a few cells at the injury site. Our data strongly suggest that during the initial several months after nerve injury, peripherally over-produced prostaglandins play an important role in the maintenance of neuropathic pain.

Effects of hypoxia and nitric oxide on ferritin content of alveolar cells

Concentrations of ferritin in alveolar cells and on the alveolar surface are increased in patients with a variety of respiratory disorders. Ferritin synthesis by cells is modulated by iron content but is also influenced by stimuli other than iron. In this study we sought to determine whether in vitro exposure to hypoxia- or nitric oxide (NO)-induced ferritin accumulation or release by human alveolar macrophages (AMs) or a lung cancer-derived epithelial cell line (A549). Changes in cell content of iron and ferritin (L- and H-types), as well as ferritin content of cell supernatants, were determined after in vitro exposure to hypoxia (1% or 10% O(2), 18 hours) or the NO donor S-nitroso-N-acetylpenicillamine (SNAP, 0.01-1.0 mmol/L, 18 hours). Exposure to 1% O(2) increased ferritin content in both cell types (>fourfold increase; P <.005) without changing iron content. Treatment with SNAP increased ferritin content of A549 cells in a dose-dependent manner, whereas treatment of AMs decreased cellular iron and ferritin content and increased supernate ferritin content. Pretreatment of cells with N-acetylcysteine (500 micromol/L) reduced hypoxia-induced ferritin accumulation in alveolar cells and completely inhibited NO-induced ferritin accumulation in A549 cells. These findings indicate that exposure to 1% O(2)can increase ferritin content in alveolar cells, whereas NO can increase ferritin content (A549 cells) or decrease ferritin content (AMs).

TNF-alpha secretion and macrophage mortality induced by cobalt and chromium ions in vitro-qualitative analysis of apoptosis

Metal ion toxicity is a major cause for concern in metal-metal hip replacements. A previous study in our laboratory demonstrated that Co(2+) and Cr(3+) induce macrophage apoptosis in vitro at 24h, with the implication of a caspase-3 pathway. The aim of the present study was to look at the effect of a prolonged incubation time on macrophage response with regards to TNF-alpha secretion and macrophage mortality, more specifically apoptosis. J774 macrophages were exposed for up to 48 h to 0-10 ppm Co(2+) and 0-500 ppm Cr(3+). ELISA results demonstrated that Co(2+ )and Cr(3+) induced a concentration- and time-dependent increase of TNF-alpha secretion, but a decrease at the highest concentrations of Cr(3+) (350-500 ppm). This decrease was most likely due to a high toxicity of Cr(3+) at such concentrations. Higher levels of TNF-alpha were observed with Co(2+) than Cr(3+), demonstrating a higher stimulatory effect of this ion. Trypan blue and flow cytometry results demonstrated that both Co(2+) and Cr(3+) ions induce macrophage mortality in a dose- and time-dependent manner. The number of cells decreased when ion concentrations increased, especially at 48 h. In parallel with the TNF-alpha results, Co(2+) was more toxic than Cr(3+) since the maximal effects were reached with lower concentrations (8-10 ppm vs. 350-500 ppm, respectively). DNA analysis demonstrated that both Co(2+) and Cr(3+) ions induce macrophage apoptosis, with a stronger signal at 24h than at 48 h, suggesting the presence of more necrosis after 48 h. PARP cleavage, another marker of apoptosis, was observed at both 24 and 48 h, with a maximum intensity at 48 h and with the highest concentrations of ions. In conclusion, this study demonstrates that both Co(2+) and Cr(3+) ions can induce the release of TNF-alpha and macrophage mortality in a dose- and time-dependent manner. More specifically, Co(2+) and Cr(3+) ions induced apoptosis after both 24 and 48 h incubation, although DNA analysis suggested the presence of necrosis at 48 h. The relative importance of apoptosis and necrosis in the induction of macrophage mortality by these metal ions remains to be investigated.

The regulatory role of nitric oxide in apoptosis

Nitric oxide (NO) is a multi-faceted molecule with dichotomous regulatory roles in many areas of biology. The complexity of its biological effects is a consequence of its numerous potential interactions with other molecules such as reactive oxygen species (ROS), metal ions, and proteins. The effects of NO are modulated by both direct and indirect interactions that can be dose-dependent and cell-type specific. For example, in some cell types NO can promote apoptosis, whereas in other cells NO inhibits apoptosis. In hepatocytes, NO can inhibit the main mediators of cell death-caspase proteases. Moreover, low physiological concentrations of NO can inhibit apoptosis, but higher concentrations of NO may be toxic. High NO concentrations lead to the formation of toxic reaction products like dinitrogen trioxide or peroxynitrite that induce cell death, if not by apoptosis, then by necrosis. Long-term exposure to nitric oxide in certain conditions like chronic inflammatory states may predispose cells to tumorigenesis through DNA damage, inhibition of DNA repair, alteration in programmed cell death, or activation of proliferative signaling pathways. Understanding the regulatory mechanisms of NO in apoptosis and carcinogenesis will provide important clues to the diagnosis and treatment of tissue damage and cancer. In this article we have reviewed recent discoveries in the regulatory role of NO in specific cell types, mechanisms of pro-apoptotic and anti-apoptotic induction by NO, and insights into the effects of NO on tumor biology.

Effects of nitric oxide donors on the afferent resting activity in the cephalopod statocyst

The effects of bath applications of the nitric oxide (NO) donors sodium nitroprusside (SNP), diethylamine sodium (DEA), 3-morpholinosydnonimine (SIN-1), and S-nitroso-N-acetyl-penicillamine (SNAP) on the resting activity (RA) of afferent crista fibers were studied in isolated statocysts of the cuttlefish Sepia officinalis. The NO donors had three different effects: inhibition, excitation, and excitation followed by an inhibition. The SNAP analog N-acetyl-DL-penicillamine (xSNAP; with no NO moiety) had no effect. When the preparation was pre-treated with the NO synthase inhibitor N(G)-nitric-L-arginine methyl ester HCl (L-NAME), the NO donors were still effective. When the preparation was pre-treated with the guanylate cyclase inhibitors methylene blue (M-BLU) or cystamine (CYS), NO donors had only excitatory effects, whereas their effects were inhibitory only when pre-treatment was with the adenylate cyclase inhibitors nicotinic acid (NIC-A), 2',3'-dideoxyadenosine (DDA), or MDL-12330A. When pre-treatment was with a guanylate and an adenylate cyclase inhibitor combined, NO donors had no effect; in that situation, the RA of the afferent fibers remained and the preparation still responded to bath applications of GABA. Selective experiments with statocysts from the squid Sepioteuthis lessoniana and the octopod Octopus vulgaris gave comparable results. These data indicate that in cephalopod statocysts an inhibitory NO-cGMP and an excitatory NO-cAMP signal transduction pathway exist, that these two pathways are the key pathways for the action of NO, and that they have only modulatory effects on, and are not essential for the generation of, the RA.

Differential regulation of cyclooxygenase-2 (COX-2) mRNA stability by interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) in human in vitro differentiated macrophages

Cyclooxygenase-2 (COX-2) is a highly inducible gene in macrophages by pro-inflammatory cytokines. A major mechanism for cytokine-induced COX-2 expression is stabilization of COX-2 mRNA. In this study, we examined the induction of COX-2 expression by interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) in human primary in vitro differentiated macrophages. IL-1 beta (5 ng/mL) or TNF-alpha (1 ng/mL) induced up to an approximately 40-fold increase of COX-2 mRNA in macrophages during a 2 to 2.5-hr incubation. Run-off experiments demonstrated that cytokine stimulation had only a mild effect on the COX-2 transcription rate (approximately 10-40% increase). The translation blocker cycloheximide (CHM) (10 mg/mL) superinduced COX-2 mRNA during 2 hr of incubation and further stabilized the COX-2 mRNA (T1/2 > 4 hr). The CHM-superinduced COX-2 mRNA was subject to a rapid degradation after removal of CHM (T1/2 < 1 hr). Both IL-1 beta and TNF-alpha stabilized cytokine-induced COX-2 mRNA (T1/2 > or = 2 hr). Maximal stabilization of COX-2 mRNA after a short-term stimulation required the continued presence of IL-1 beta in the medium. Long-term treatment of TNF-alpha destabilized the induced COX-2 mRNA. Cells simultaneously treated with both IL-1 beta and TNF-alpha had a reduced induction of COX-2, IL-1 beta, and IL-6 mRNA. In transcription-arrested cells, the translation blocker puromycin affected the TNF-alpha-induced stabilization and destabilization of COX-2 mRNA, but not the IL-1 beta-induced stabilization. The studies suggest that positive and negative regulation of mRNA stability may play a major role in cytokine-mediated COX-2 induction in human macrophages. TNF-alpha may play both pro-inflammatory and protective roles during inflammation by regulation of pro-inflammatory gene transcripts.