Oxidative stress inhibits the phagocytosis of apoptotic cells that have externalized phosphatidylserine

Anti-oral cancer properties of potential probiotic lactobacilli isolated from traditional milk, cheese, and yogurt

This study investigates the probiotic and anti-cancer effects of 21 isolated Lactobacillus strains from cheese, milk, and yogurt in Kermanshah, Iran, on oral cancer cell lines KB and OSCC. Four selected isolates (Y33, M45, C5, and C28) displayed good viability and resistance to specific antibiotics. Notably, strains C28 and Y33 exhibited the best results, showing susceptibility or semi-susceptibility to five antibiotics. Y33, with high cell surface hydrophobicity (62%), demonstrated significant anti-pathogenic activity, inhibiting the growth of tested pathogens and displaying strong adhesion to human intestinal Caco-2 cells (52%). Further assessments, including acridine orange/ethidium bromide staining and mRNA expression analysis, revealed four isolates (C5, C28, M45, and Y33) with promising probiotic properties. Particularly, Y33's protein-based extract metabolites showed dose- and time-dependent inhibition of KB and OSCC cancer cell lines, inducing apoptosis without significant cytotoxic effects on normal cells. Y33 (Lactiplantibacillus plantarum) exhibited the strongest probiotic potential, surpassing conventional anti-cancer drugs, suggesting its therapeutic potential for preventing oral cancer cell proliferation and improving survival rates in oral cancer patients.

Cytotoxic effect of potential probiotic Lactiplantibacillus plantarum KUMS-Y8 isolated from traditional dairy samples on the KB and OSCC human cancer cell lines

Oral cancer is one of the leading causes of death worldwide, and its prevalence is especially high in developing countries. As an oral cancer treatment, traditional therapies are commonly used. Nonetheless, these treatments frequently result in a variety of side effects. As a consequence, there is an urgent need to enhance oral cancer therapies. Probiotics have recently demonstrated intriguing properties as therapeutic options for cancer treatment. Thus, the purpose of this study was to investigate the anticancer effect of probiotic Lactobacillus strains on the mouth epidermal carcinoma cells (KB) and oral squamous cell carcinoma (OSCC) cell lines. In this study, we looked at 21 Lactobacillus strains isolated from traditional dairy products in the Kermanshah province of western Iran to see if they had any inhibitory effects on oral cancer cell lines in vitro. We isolated and characterized Lactobacillus strains before assessing and comparing their probiotic potential and safety. Using the MTT assay, the bacterial extract was then prepared and used as an anti-proliferative agent on oral cancer (KB and OSCC) and normal (fibroblast and human umbilical vein endothelial cells (HUVEK) cell lines. Finally, acridine orange/ethidium bromide staining was used to determine whether cell death was caused by apoptosis. Four Lactobacillus isolates (C14, M22, M42, and Y8) were shown to have beneficial probiotic qualities. Lactobacillus extracts (of a protein nature) decreased the survival and proliferation of the KB and OSCC cancer cell lines (dose- and time-dependent) by inducing apoptosis, with no basic damaging effects on normal cells. The staining with acridine orange/ethidium bromide revealed that the cell death was caused by apoptosis. Furthermore, of the four Lactobacillus strains examined, isolate Y8 (Lactiplantibacillus plantarum) showed the strongest probiotic potential for suppressing KB and OSCC cell proliferation when compared to anticancer medicines (doxorubicin and paclitaxel). The current research found that Lactobacillus extract might reduce the growth and viability of the KB and OSCC cancer cell lines by inducing apoptosis, increasing the survival rate of oral cancer patients.

Targeting Pseudomonas aeruginosa quorum sensing with sodium salicylate modulates immune responses in vitro and in vivo

Introduction

Chronic infections are a major clinical challenge in hard-to-heal wounds and implanted devices. Pseudomonas aeruginosa is a common causative pathogen that produces numerous virulence factors. Due to the increasing problem of antibiotic resistance, new alternative treatment strategies are needed. Quorum sensing (QS) is a bacterial communication system that regulates virulence and dampens inflammation, promoting bacterial survival. QS inhibition is a potent strategy to reduce bacterial virulence and alleviate the negative impact on host immune response.

Aim

This study investigates how secreted factors from P. aeruginosa PAO1, cultured in the presence or absence of the QS inhibitor sodium salicylate (NaSa), influence host immune response.

Material and methods

In vitro, THP-1 macrophages and neutrophil-like HL-60 cells were used. In vivo, discs of titanium were implanted in a subcutaneous rat model with local administration of P. aeruginosa culture supernatants. The host immune response to virulence factors contained in culture supernatants (+/-NaSa) was characterized through cell viability, migration, phagocytosis, gene expression, cytokine secretion, and histology.

Results

In vitro, P. aeruginosa supernatants from NaSa-containing cultures significantly increased THP-1 phagocytosis and HL-60 cell migration compared with untreated supernatants (-NaSa). Stimulation with NaSa-treated supernatants in vivo resulted in: (i) significantly increased immune cell infiltration and cell attachment to titanium discs; (ii) increased gene expression of IL-8, IL-10, ARG1, and iNOS, and (iii) increased GRO-α protein secretion and decreased IL-1β, IL-6, and IL-1α secretion, as compared with untreated supernatants.

Conclusion

In conclusion, treating P. aeruginosa with NaSa reduces the production of virulence factors and modulates major immune events, such as promoting phagocytosis and cell migration, and decreasing the secretion of several pro-inflammatory cytokines.

Aerosol physicochemical determinants of carbon black and ozone inhalation co-exposure induced pulmonary toxicity

Air pollution accounts for more than 7 million premature deaths worldwide. Using ultrafine carbon black (CB) and ozone (O3) as a model for an environmental co-exposure scenario, the dose response relationships in acute pulmonary injury and inflammation were determined by generating, characterizing, and comparing stable concentrations of CB aerosols (2.5, 5.0, 10.0 mg/m3), O3 (0.5, 1.0, 2.0 ppm) with mixture CB + O3 (2.5 + 0.5, 5.0 + 1.0, 10.0 + 2.0). C57BL6 male mice were exposed for 3 h by whole body inhalation and acute toxicity determined after 24 h. CB itself did not cause any alteration, however, a dose response in pulmonary injury/inflammation was observed with O3 and CB + O3. This increase in response with mixtures was not dependent on the uptake but was due to enhanced reactivity of the particles. Benchmark dose modeling showed several-fold increase in potency with CB + O3 compared with CB or O3 alone. Principal component analysis provided insight into response relationships between various doses and treatments. There was a significant correlation in lung responses with charge-based size distribution, total/alveolar deposition, oxidant generation, and antioxidant depletion potential. Lung tissue gene/protein response demonstrated distinct patterns that are better predicted by either particle dose/aerosol responses (interleukin-1β, keratinocyte chemoattractant, transforming growth factor beta) or particle reactivity (thymic stromal lymphopoietin, interleukin-13, interleukin-6). Hierarchical clustering showed a distinct signature with high dose and a similarity in mRNA expression pattern of low and medium doses of CB + O3. In conclusion, we demonstrate that the biological outcomes from CB + O3 co-exposure are significantly greater than individual exposures over a range of aerosol concentrations and aerosol characteristics can predict biological outcome.

Iron-induced cellular in vitro neurotoxic responses in rat C6 cell line

Iron is an essential metal critical for normal cellular and biochemical function and it is used as a cofactor in many vital biological pathways within the brain. However, accumulation of excess iron in brain is commonly associated with several neurodegenerative and neurotoxic adverse effects. Chronic exposure of iron leads to an increased risk for several neurodegenerative diseases. The exact mechanism of iron-induced neurotoxicity is still unclear. Therefore, our study aimed to investigate the mechanism of neurotoxic and neurodegenerative effects through in vitro exposure of ferrous sulphate in rat C6 cell line. The findings of our study have indicated that ferrous sulphate exposure may lead to induction of molecular markers of neuronal inflammation, apoptotic neuronal cell death, amyloid-beta and hyperphosphorylated tau levels. This study provides a basic mechanistic understanding of signaling pathway and biomarkers involved during iron-induced neurotoxicity.

Erythrophagocytosis by Microglia/Macrophage in Intracerebral Hemorrhage: From Mechanisms to Translation

Intracerebral hemorrhage (ICH) is a devastating condition characterized by hematoma related mass effect. Microglia/macrophage (M φ) are rapidly recruited in order to remove the red blood cells through erythrophagocytosis. Efficient erythrophagocytosis can detoxify hemolytic products and facilitate neurological recovery after ICH. The underlying mechanisms include modulation of inflammatory response and oxidative stress, among others. It is a dynamic process mediated by a cascade of signal transduction, including “find-me” signals, “eat-me” signals and a set of phagocytotic receptors-ligand pairs that may be exploited as therapeutic targets. This review summarizes mechanistic signaling pathways of erythrophagocytosis and highlights the potential of harnessing M φ-mediated phagocytosis for ICH treatment.

Cytotoxic impacts of treated electroplating industrial effluent and the comparative effect of their metal components (Zn, Hg, and Zn+Hg) on Danio rerio gill (DrG) cell line

Effluent produced during the electroplating process can contain high concentrations of heavy metals that can enter the environment and induce toxicity to aquatic organisms. Relatively high concentrations of zinc (Zn) and mercury (Hg) have been detected in treated electroplating industrial effluent (TEPIE), though the cytotoxic potential of these compounds has not been well assessed in fish gills. A novel cell line, Danio rerio gill (DrG), were exposed to TEPIE and concentrations of Zn, Hg, and Zn + Hg previously measured in treated effluent to evaluate the use of the DrG cell line following exposure to environmental pollutants. Several cytotoxic assays were employed to assess the effect of TEPIE, Zn, and Hg on this cell line. The percent cell viability was significantly reduced in a concentration-dependent manner following exposure to TEPIE, Zn, Hg, and Zn + Hg (p < 0.05) for 24 h, with additional morphological changes observed in exposure treatments relative to controls. Additionally, there was a significant induction of DNA damage detected in all exposure treatments determined through comet assay tail length. An increase in intracellular ROS generation was also observed in cells exposed to TEPIE, Zn, Hg, and Zn + Hg, corresponding to dose-dependent increases in apoptosis. Our study confirmed that TEPIE and the metals present in it induced cytotoxicity in the DrG cell line, demonstrating its usefulness as a model to explore relationships between pollutants and fish gills.

Cadmium induced oxystress alters Nrf2-Keap1 signaling and triggers apoptosis in piscine head kidney macrophages

Cadmium (Cd) with no known functional role in any life-form has myriad of harmful effects. The present study was designed to elucidate the mechanism of Cd-induced oxystress generation and its impact on antioxidant and apoptosis signaling pathways in head kidney macrophage (HKM) of Channa punctatus Bloch. Fish were sampled and acclimatized with one group treated with cadmium chloride (CdCl₂) (1.96 mg/L) and another as untreated control group, both kept under observation for 7 days. Exposure to Cd caused ultrastructural changes along with reduced head kidney somatic index (HKSI). Significantly increased levels of reactive oxygen species (ROS), respiratory burst activity, lipid peroxidation, DNA fragmentation and superoxide dismutase were found in the HKM from the treated group as compared to control. In contrast, antioxidant enzymes like catalase and reduced glutathione activity decreased in the Cd exposed group. The suppressed antioxidant activity was further confirmed and corroborated from the altered expression of Kelch-like ECH-associated protein 1 (Keap1) and nuclear factor erythroid 2-related factor 2 (Nrf2) genes, the major player of antioxidant pathway. Cd induced alteration in Nrf2-Keap1 signaling pathway was also validated by the diminished levels of Nrf2 dependent expression of protein like heme oxygenase-1 (HO-1). The flow cytometry analysis supported the event of apoptosis in Cd exposed group as compared to control, which was further confirmed by the upregulated expression of caspase-3, caspase-8, caspase-9, TNF-α and p53 genes from the real-time gene expression study. In addition, altered protein level of cytochrome C validates the incidence of apoptosis. Altogether, our results demonstrate that exposure to Cd caused oxidative stress in HKM of Channa punctatus Bloch. by compromising the antioxidant enzyme activities via the down regulation of expression of genes related to antioxidant signaling pathway besides encouraging apoptosis via both mitochondrial and death receptor pathway.

Reactive Oxygen-Forming Nox5 Links Vascular Smooth Muscle Cell Phenotypic Switching and Extracellular Vesicle-Mediated Vascular Calcification

RATIONALE

Vascular calcification, the formation of calcium phosphate crystals in the vessel wall, is mediated by vascular smooth muscle cells (VSMCs). However, the underlying molecular mechanisms remain elusive, precluding mechanism-based therapies.

OBJECTIVE

Phenotypic switching denotes a loss of contractile proteins and an increase in migration and proliferation, whereby VSMCs are termed synthetic. We examined how VSMC phenotypic switching influences vascular calcification and the possible role of the uniquely calcium-dependent reactive oxygen species (ROS)-forming Nox5 (NADPH oxidase 5).

METHODS AND RESULTS

In vitro cultures of synthetic VSMCs showed decreased expression of contractile markers CNN-1 (calponin 1), α-SMA (α-smooth muscle actin), and SM22-α (smooth muscle protein 22α) and an increase in synthetic marker S100A4 (S100 calcium binding protein A4) compared with contractile VSMCs. This was associated with increased calcification of synthetic cells in response to high extracellular Ca²⁺. Phenotypic switching was accompanied by increased levels of ROS and Ca²⁺-dependent Nox5 in synthetic VSMCs. Nox5 itself regulated VSMC phenotype as siRNA knockdown of Nox5 increased contractile marker expression and decreased calcification, while overexpression of Nox5 decreased contractile marker expression. ROS production in synthetic VSMCs was cytosolic Ca²⁺-dependent, in line with it being mediated by Nox5. Treatment of VSMCs with Ca²⁺ loaded extracellular vesicles (EVs) lead to an increase in cytosolic Ca²⁺. Inhibiting EV endocytosis with dynasore blocked the increase in cytosolic Ca²⁺ and VSMC calcification. Increased ROS production resulted in increased EV release and decreased phagocytosis by VSMCs.

CONCLUSIONS

We show here that contractile VSMCs are resistant to calcification and identify Nox5 as a key regulator of VSMC phenotypic switching. Additionally, we describe a new mechanism of Ca²⁺ uptake via EVs and show that Ca²⁺ induces ROS production in VSMCs via Nox5. ROS production is required for release of EVs, which promote calcification. Identifying molecular pathways that control Nox5 and VSMC-derived EVs provides potential targets to modulate vascular remodeling and calcification in the context of mineral imbalance. Graphic Abstract: A graphic abstract is available for this article.

Calcium Signaling and Tissue Calcification

Calcification is a regulated physiological process occurring in bones and teeth. However, calcification is commonly found in soft tissues in association with aging and in a variety of diseases. Over the last two decades, it has emerged that calcification occurring in diseased arteries is not simply an inevitable build-up of insoluble precipitates of calcium phosphate. In some cases, it is an active process in which transcription factors drive conversion of vascular cells to an osteoblast or chondrocyte-like phenotype, with the subsequent production of mineralizing "matrix vesicles." Early studies of bone and cartilage calcification suggested roles for cellular calcium signaling in several of the processes involved in the regulation of bone calcification. Similarly, calcium signaling has recently been highlighted as an important component in the mechanisms regulating pathological calcification. The emerging hypothesis is that ectopic/pathological calcification occurs in tissues in which there is an imbalance in the regulatory mechanisms that actively prevent calcification. This review highlights the various ways that calcium signaling regulates tissue calcification, with a particular focus on pathological vascular calcification.

Assessment of probiotic potential and anticancer activity of newly isolated vaginal bacterium Lactobacillus plantarum 5BL

Numerous bacteria in and on its external parts protect the human body from harmful threats. This study aimed to investigate the potential beneficial effects of the vaginal ecosystem microbiota. A type of bacteria was isolated from vaginal secretions of adolescent and young adult women, cultured on an appropriate specific culture medium, and then molecularly identified through 16S rDNA gene sequencing. Results of 16S rDNA sequencing revealed that the isolate belongs to the Lactobacillus plantarum species. The isolated strain exhibited probiotic properties such as low pH and high bile salt concentration tolerance, antibiotic susceptibility and antimicrobial activity against some pathogenic bacteria. The anticancer effects of the strain on human cancer cell lines (cervical, HeLa; gastric, AGS; colon, HT-29; breast, MCF-7) and on a human normal cell line (human umbilical vein endothelial cells [HUVEC]) were investigated. Toxic side effects were assessed by studying apoptosis in the treated cells. The strain exhibited desirable probiotic properties and remarkable anticancer activity against the tested human cancer cell lines (P ≤ 0.05) with no significant cytotoxic effects on HUVEC normal cells (P ≤ 0.05). Overall, the isolated strain showed favorable potential as a bioactive therapeutic agent. Therefore, this strain should be subjected to the other required tests to prove its suitability for clinical therapeutic application.

Probiotic potential and biotherapeutic effects of newly isolated vaginal Lactobacillus acidophilus 36YL strain on cancer cells

Lactobacillus acidophilus is categorized as a probiotic strain because of its beneficial effects in human health and prevention of disease transmission. This study is aimed to characterize the probiotic potential of L. acidophilus 36YL originally isolated from the vagina of healthy and fertile Iranian women. The L. acidophilus 36YL strain was identified using 16S rDNA gene sequencing and characterized by biochemical methodologies, such as antibiotics susceptibility, antimicrobial activity, and acid and bile resistance. The bioactivity of the secretion of this strain on four human cancer cell lines (AGS, HeLa, MCF-7, and HT-29) and one normal cell line (HUVEC) was evaluated by cytotoxicity assay and apoptosis analysis. This newly isolated strain was found to exhibit notable probiotic properties, such as admirable antibiotic susceptibility, good antimicrobial activity, and favorable resistance to acid and bile salt. The results of bioactivity assessment demonstrated acceptable anticancer effects on the four tested cancer cell lines and negligible side effects on the assayed normal cell line. Our findings revealed that the anticancer effect of L. acidophilus 36YL strain secretions depends on the induction of apoptosis in cancer cells. L. acidophilus 36YL strain is considered as a nutraceutical alternative or a topical medication with a potential therapeutic index because of the absence of cytotoxicity to normal cells, but effective toxicity to cancer cell lines.

Sputum neutrophils in cystic fibrosis patients display a reduced respiratory burst

BACKGROUND

Few data exist on the functional activity of airway neutrophils in the milieu of the cystic fibrosis (CF) lung. We assessed reactive oxygen species (ROS) production by sputum neutrophils and the relationship to neutrophil viability. Identical assessments were made on peripheral blood neutrophils from CF patients.

METHODS

ROS production in sputum neutrophils was assessed in 31 CF patients at varying phases of clinical disease using flow cytometry. Twenty patients provided blood samples (including 16 who also provided a matched sputum sample). Neutrophil viability was determined using dual annexin V (apoptosis) and propidium iodide (necrosis) staining. Comparative peripheral blood data were obtained from 7 healthy controls.

RESULTS

ROS production was reduced in sputum compared to blood neutrophils and they demonstrated a higher level of necrosis. Subpopulations of neutrophils with different ROS production capacity were apparent in peripheral blood. Lung function was positively associated with both the proportion of blood neutrophils demonstrating increased ROS production and the proportion of apoptotic sputum neutrophils.

CONCLUSIONS

CF airway neutrophils display functional exhaustion. Healthier lungs in CF appear to be associated with subpopulations of blood neutrophils with increased oxidative burst capacity and evidence for increased neutrophil apoptosis within the airway.

Fish and mammalian phagocytes differentially regulate pro-inflammatory and homeostatic responses in vivo

Phagocytosis is a cellular mechanism that is important to the early induction of antimicrobial responses and the regulation of adaptive immunity. At an inflammatory site, phagocytes serve as central regulators for both pro-inflammatory and homeostatic anti-inflammatory processes. However, it remains unclear if this is a recent evolutionary development or whether the capacity to balance between these two seemingly contradictory processes is a feature already displayed in lower vertebrates. In this study, we used murine (C57BL/6) and teleost fish (C. auratus) in vitro and in vivo models to assess the evolutionary conservation of this dichotomy at a site of inflammation. At the level of the macrophage, we found that teleost fish already displayed divergent pro-inflammatory and homeostatic responses following internalization of zymosan or apoptotic bodies, respectively, and that these were consistent with those of mice. However, fish and mice displayed significant differences in vivo with regards to the level of responsiveness to zymosan and apoptotic bodies, the identity of infiltrating leukocytes, their rate of infiltration, and the kinetics and strength of resulting antimicrobial responses. Unlike macrophages, significant differences were identified between teleost and murine neutrophilic responses. We report for the first time that activated murine, but not teleost neutrophils, possess the capacity to internalize apoptotic bodies. This internalization translates into reduction of neutrophil ROS production. This may play an important part in the recently identified anti-inflammatory activity that mammalian neutrophils display during the resolution phase of inflammation. Our observations are consistent with continued honing of inflammatory control mechanisms from fish to mammals, and provide added insights into the evolutionary path that has resulted in the integrated, multilayered responses that are characteristic of higher vertebrates.

Pyrrolidine dithiocarbamate augments Hg(2+)-mediated induction of macrophage cell death via oxidative stress-induced apoptosis and necrosis signaling pathways

Exposure to mercury can lead to several injuries in mammals, including immune system dysfunction, and pyrrolidine dithiocarbamate (PDTC), as a metal chelator and antioxidant, has been indicated to increase the cytotoxic effects of toxic metals. However, the toxicological effects and possible mechanisms of mercury in combination with PDTC are mostly unclear. In this study, we showed that PDTC dramatically increase the cytotoxic effect of HgCl(2) on cultured murine macrophages (RAW 264.7 cells). PDTC augmented HgCl(2)-induced cytotoxic effects by facilitating the entry of mercury into the cells. The Hg(2+)/PDTC complex significantly and rapidly increased the formation of reactive oxygen species (ROS) and decreased intracellular glutathione (GSH) levels in these cells. Flow cytometry analysis showed that the numbers of sub-G1 hypodiploid cells and annexin V-FITC binding cells increased after Hg(2+)/PDTC complex exposure, and several features of mitochondria-dependent apoptosis were also induced, including mitochondrial membrane depolarization, cytosolic cytochrome c release, poly(ADP-ribose) polymerase (PARP) and caspase 3/7 activation, and DNA fragmentation. Moreover, both apoptotic and necrotic cells were detected using acridine orange/ethidium bromide dual staining. Meanwhile, depleted intracellular ATP levels and increased lactate dehydrogenase (LDH) release were observed, suggesting the induction of necrotic cell death processes. These Hg(2+)/PDTC complex-induced cytotoxicity-related signals could be reversed by pretreatment with the antioxidant N-acetylcysteine. In conclusion, these results suggest that Hg(2+)/PDTC complex-induced oxidative stress causes macrophage cell death via both apoptosis and necrosis. These findings imply for the first time that PDTC dramatically increases the uptake and toxicological effects of Hg(2+) instead of detoxification.

Molecular and cellular mechanism of lung injuries due to exposure to sulfur mustard: a review

Sulfur mustard (SM), a potent chemical weapon agent, was used by Iraqi forces against Iranian in the Iraq-Iran war (1981-1989). Chronic obstructive pulmonary disease (COPD) is a late toxic pulmonary consequence after SM exposure. The COPD observed in these patients is unique (described as Mustard Lung) and to some extent different from COPD resulted from other well-known causes. Several mechanisms have been hypothesized to contribute to the pathogenesis of COPD including oxidative stress, disruption of the balance between apoptosis and replenishment, proteinase-antiproteinase imbalance and inflammation. However, it is not obvious which of these pathways are relevant to the pathogenesis of mustard lung. In this paper, we reviewed studies addressing the pathogenicity of mustard lung, and reduced some recent ambiguities in this field. There is ample evidence in favor of crucial role of both oxidative stress and apoptosis as two known mechanisms that are more involved in pathogenesis of mustard lung comparing to COPD. However, according to available evidences there are no such considerable data supporting neither proteolytic activity nor inflammation mechanism as the main underlying pathogenesis in Mustard Lung.

Mechanisms of failed apoptotic cell clearance by phagocyte subsets in cardiovascular disease

Recent evidence in humans indicate that defective phagocytic clearance of dying cells is linked to progression of advanced atherosclerotic lesions, the precursor to atherothrombosis, ischemic heart disease, and leading cause of death in the industrialized world. During atherogenesis, apoptotic cell turnover in the vascular wall is counterbalanced by neighboring phagocytes with high clearance efficiency, thereby limiting cellularity and maintaining lesion integrity. However, as lesions mature, phagocytic removal of apoptotic cells (efferocytosis) becomes defective, leading to secondary necrosis, expansion of plaque necrotic cores, and susceptibility to rupture. Recent genetic causation studies in experimental rodents have implicated key molecular regulators of efferocytosis in atherosclerotic progression. These include MER tyrosine kinase (MERTK), milk fat globule-EGF factor 8 (MFGE8), and complement C1q. At the cellular level, atheromata are infiltrated by a heterogenous population of professional phagocytes, comprised of monocytes, differentiated macrophages, and CD11c(+) dendritic-like cells. Each cell type is characterized by disparate clearance efficiencies and varying activities of key phagocytic signaling molecules. It is in this context that we outline a working model whereby plaque necrosis and destabilization is jointly promoted by (1) direct inhibition of core phagocytic signaling pathways and (2) expansion of phagocyte subsets with poor clearance capacity. Towards identifying targets for promoting efficient apoptotic cell clearance and resolving inflammation in atherosclerosis and during ischemic heart disease and post myocardial infarction, this review will discuss potential in vivo suppressors of efferocytosis at each stage of clearance and how these putative interventional targets may differentially affect uptake at the level of vascular phagocyte subsets.

Microenvironmental influences of apoptosis in vivo and in vitro

The apoptosis program of physiological cell death elicits a range of non-phlogistic homeostatic mechanisms-"recognition, response and removal"-that regulate the microenvironments of normal and diseased tissues via multiple modalities operating over short and long distances. The molecular mechanisms mediate intercellular signaling through direct contact with neighboring cells, release of soluble factors and production of membrane-delimited fragments (apoptotic bodies, blebs and microparticles) that allow for interaction with host cells over long distances. These processes effect the selective recruitment of mononuclear phagocytes and the specific activation of both phagocytic and non-phagocytic cells. While much evidence is available concerning the mechanisms underlying the recognition and responses of phagocytes that culminate in the engulfment and removal of apoptotic cell bodies, relatively little is yet known about the non-phagocytic cellular responses to the apoptosis program. These responses regulate inflammatory and immune cell activation as well as cell fate decisions of proliferation, differentiation and death. Here, we review current knowledge of these processes, considering especially how apoptotic cells condition the microenvironments of normal and malignant tissues. We also discuss how apoptotic cells that persist in the absence of phagocytic clearance exert inhibitory effects over their viable neighbors, paying particular attention to the specific case of cell cultures and highlighting how new cell-corpse-clearance devices-Dead-Cert Nanoparticles-can significantly improve the efficacy of cell cultures through effective removal of non-viable cells in the absence of phagocytes in vitro.

Nanoparticle-mediated delivery of superoxide dismutase to the brain: an effective strategy to reduce ischemia-reperfusion injury

Excessive production of reactive oxygen species (ROS) after cerebral ischemia and reperfusion is implicated in brain damage through different cellular and molecular mechanisms, and it is further aggravated by impaired cellular antioxidant defense systems under ischemic conditions. Therapeutic strategies based on exogenous delivery of the native form of superoxide dismutase (SOD), a free radical scavenger, are limited because of its short half-life (approximately 6 min) in vivo and poor permeability across the blood-brain-barrier (BBB). We encapsulated SOD in biodegradable poly(D,L-lactide co-glycolide) nanoparticles (SOD-NPs) and tested their efficacy in a rat focal cerebral ischemia-reperfusion injury model. We hypothesized that localized brain delivery of SOD-NPs would sustain the protective effect of SOD by neutralizing the deleterious effects of ROS formed following ischemia-reperfusion. SOD-NPs were administered at the time of reperfusion via the intracarotid route to maximize their localization in the brain. Animals receiving SOD-NPs (10,000 U of SOD/kg) demonstrated a 65% reduction in infarct volume, whereas an equivalent dose of SOD in solution (SOD-Sol) increased it by 25% over saline control (P<0.001; data at 6 h following reperfusion). Control NPs alone or mixed with SOD-Sol were ineffective in reducing infract volume, with results similar to saline control, indicating the protective effect of the encapsulated enzyme. SOD-NPs maintained BBB integrity, thereby preventing edema, reduced the level of ROS formed following reperfusion, and protected neurons from undergoing apoptosis. Animals treated with SOD-NPs demonstrated greater survival than those with saline control (75% vs. 0% at 28 days) and later regained most vital neurological functions. SOD-NPs may be an effective treatment option in conjunction with a thrombolytic agent for stroke patients.

Impairment of apoptotic cell engulfment by pyocyanin, a toxic metabolite of Pseudomonas aeruginosa

RATIONALE

Cystic fibrosis lung disease is characterized by accumulation of apoptotic neutrophils, indicating impaired clearance of dying cells. Pseudomonas aeruginosa, the principal microbial pathogen in cystic fibrosis, manipulates apoptosis induction via production of toxic metabolites. Whether these metabolites, particularly pyocyanin, can also modulate apoptotic cell engulfment is unknown.

OBJECTIVES

To assess the effects of pyocyanin on apoptotic cell engulfment by macrophages in vitro and in vivo and to investigate potential mechanisms of the observed effects.

METHODS

Human monocyte-derived macrophages were treated with pyocyanin before challenge with apoptotic neutrophils, apoptotic Jurkat cells, or latex beads, and phagocytosis was assessed by light microscopy and flow cytometry. Effects of pyocyanin production on apoptotic cell clearance in vivo were assessed in a murine model, comparing infection by wild-type or pyocyanin-deficient P. aeruginosa. Oxidant production was investigated using fluorescent probes and pharmacologic inhibition and Rho GTPase signaling by immunoblotting and inhibitor studies.

MEASUREMENTS AND MAIN RESULTS

Pyocyanin treatment impaired macrophage engulfment of apoptotic cells in vitro, without inducing significant macrophage apoptosis, whereas latex bead uptake was preserved. Macrophage ingestion of apoptotic cells was reduced and late apoptotic/necrotic cells were increased in mice infected with pyocyanin-producing P. aeruginosa compared with the pyocyanin-deficient strain. Inhibition of apoptotic cell uptake involved intracellular generation of reactive oxygen species (ROS) and effects on Rho GTPase signaling. Antioxidants or blockade of Rho signaling substantially restored apoptotic cell engulfment.

CONCLUSIONS

These studies demonstrate that P. aeruginosa can manipulate the inflammatory microenvironment through inhibition of apoptotic cell engulfment, and suggest potential strategies to limit pulmonary inflammation in cystic fibrosis.

Human macrophages rescue myoblasts and myotubes from apoptosis through a set of adhesion molecular systems

The mechanisms underlying stromal cell supportive functions are incompletely understood but probably implicate a mixture of cytokines, matrix components and cell adhesion molecules. Skeletal muscle uses recruited macrophages to support post-injury regeneration. We and others have previously shown that macrophages secrete mitogenic factors for myogenic cells. Here, we focused on macrophage-elicited survival signals. We demonstrated that: (1) macrophage influx is temporally correlated with the disappearance of TUNEL-positive apoptotic myogenic cells during post-injury muscle regeneration in mice; (2) direct cell-cell contacts between human macrophages and myogenic cells rescue myogenic cells from apoptosis, as assessed by decreased annexin V labelling and caspase-3 activity, and by increased DIOC-6 staining, Bcl-2 expression and phosphorylation of Akt and ERK1/2 survival pathways; (3) four pro-survival cell-cell adhesion molecular systems detected by DNA macroarray are expressed by macrophages and myogenic cells in vitro and in vivo - VCAM-1-VLA-4, ICAM-1-LFA-1, PECAM-1-PECAM-1 and CX3CL1-CX3CR1; (4) macrophages deliver anti-apoptotic signals through all four adhesion systems, as assessed by functional analyses with blocking antibodies; and (5) macrophages more strongly rescue differentiated myotubes, which must achieve adhesion-induced stabilisation of their structure to survive. Macrophages could secure these cells until they establish final association with the matrix.

Immunology of Apoptosis and Necrosis

A complex of reactions regulating the number of cells in organs and tissues under normal and pathologic conditions is one of the most important systems of multicellular organisms. In this system, which controls both cell proliferation and clearance, clearance has been given special attention during the last three decades. Some stages of the clearance are known (the choice of "unwanted" cells, their destruction not affecting the surrounding tissue, and, finally, removal of the corpses), and undeniable progress has been achieved in the understanding of the second stage mechanisms, whereas mechanisms of elimination per se of cells or their fragments still continue to be terra incognita. The clearance of such cells is mainly determined by different components of natural and adaptive immunity: phagocytes, complement, opsonins, antigen-presenting cells, etc. Recently specific "danger signals", such as hydrolases, DNA, heat shock proteins, and other potential immunogens released by cells during their elimination have been discovered. Entering the extracellular space, these signals induce inflammation and injury of the surrounding tissues, i.e., autoimmune reactions. Heat shock proteins, in addition to chaperon activity, act as signaling, costimulating, and antigen-carrying molecules in the interactions of dying cells and the immune system.

Autologous apoptotic cell engulfment stimulates chemokine secretion by vascular smooth muscle cells

Apoptosis of vascular smooth muscle cells (VSMCs) occurs in vivo under both physiological and pathological settings. The clearance of apoptotic cells may be accomplished in part by the surrounding normal VSMCs. However, the fate of internalized apoptotic cells, the rate of intracellular degradation, and the consequences of these processes to VSMC biology are unknown. Electron microscopy and confocal fluorescence imaging showed that rat VSMCs effectively bound and internalized autologous apoptotic VSMCs in vitro. Within 2 hours, the internalized apoptotic cells were delivered to lysosomes, and the majority of these internalized cells and their proteins were efficiently degraded by 24 hours. After degradation was completed, the phagocytic VSMCs remained viable with normal rates of proliferation. Clearance of apoptotic cells by VSMCs did not induce the release of vascular wall matrix proteases but was associated with a 1.6-fold increase in transforming growth factor-beta1 release. Interestingly, clearance of apoptotic cells stimulated VSMCs to secrete monocyte-chemoattractant protein-1 and cytokine-induced neutrophil chemoattractant. The coordinated release of transforming growth factor-beta1 and chemokines suggests that autologous apoptotic cell clearance stimulates VSMCs to release molecules that specifically recruit professional phagocytes while simultaneously dampening the inflammatory response and preventing vascular injury.

Taking insult from injury: lipoxins and lipoxin receptor agonists and phagocytosis of apoptotic cells

Phagocytic clearance of apoptotic cells plays a pivotal role in the resolution of inflammation. Recent evidence has shown that such processes can be regulated by endogenous mediators, suggesting that specific mimetics may have therapeutic potential in chronic inflammation and autoimmune disorders. Here we review the mechanisms underlying recognition and engulfment of apoptotic cells and regulation of these processes by lipoxins and lipoxin receptor agonists.

Desferal inhibits breast tumor growth and does not interfere with the tumoricidal activity of doxorubicin

Desferal is a clinically approved iron chelator used to treat iron overload. Doxorubicin is an anthracycline cancer chemotherapy drug used in the treatment of breast cancer. It can undergo redox cycling in the presence of iron to produce reactive oxygen species. The oxidant-generating activity of doxorubicin is thought to be responsible for the cardiotoxic side effects of the drug, but it is unclear whether it is also required for its anti-tumor activity. To test whether an iron-chelating antioxidant would interfere with the tumor-killing activity of doxorubicin, nude mice were transplanted with xenografts of human breast cancer MDA-MB 231 cells and then treated with doxorubicin and/or desferal. Not only did desferal not interfere with the anti-tumor activity of doxorubicin, it inhibited tumor growth on its own. In vitro studies confirmed that desferal inhibits breast tumor growth. However, it did not induce apoptosis, nor did it induce cell cycle arrest. Instead, desferal caused cytostasis, apparently through iron depletion. The cytostatic activity of desferal was partially ameliorated by pretreatment with iron-saturated transferrin, and transferrin receptor expression on breast cancer cells nearly doubled after exposure to desferal. In contrast to its effect on tumor cells, desferal did not inhibit growth of normal breast epithelial cells. The data indicate that the anti-tumor activity of doxorubicin is not dependent on iron-mediated ROS production. Furthermore, desferal may have utility as an adjunctive chemotherapy due to its ability to inhibit breast tumor growth and cardiotoxic side effects without compromising the tumor-killing activity of an anthracycline chemotherapy drug.

Phagocytosis of apoptotic cells by macrophages is impaired in atherosclerosis

OBJECTIVE

Apoptotic cell death has been demonstrated in advanced human atherosclerotic plaques. Apoptotic cells (ACs) should be rapidly removed by macrophages, otherwise secondary necrosis occurs, which in turn elicits inflammatory responses and plaque progression. Therefore, we investigated the efficiency of phagocytosis of ACs by macrophages in atherosclerosis.

METHODS AND RESULTS

Human endarterectomy specimens and human tonsils were costained for CD68 (macrophages) and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) (apoptosis). Free and phagocytized ACs were counted in both tissues. The ratio of free versus phagocytized AC was 19-times higher in human atherosclerotic plaques as compared with human tonsils, indicating a severe defect in clearance of AC. Impaired phagocytosis of AC was also detected in plaques from cholesterol-fed rabbits and did not further change with plaque progression. In vitro experiments with J774 or peritoneal mouse macrophages showed that several factors caused impaired phagocytosis of AC including cytoplasmic overload of macrophages with indigestible material (beads), free radical attack, and competitive inhibition among oxidized red blood cells, oxidized low-density lipoprotein and ACs for the same receptor(s) on the macrophage.

CONCLUSIONS

Our data demonstrate that phagocytosis of ACs is impaired in atherosclerotic plaques, which is at least partly attributed to oxidative stress and cytoplasmic saturation with indigestible material.

Taurine chloramine, an oxidant derived from neutrophils, induces apoptosis in human B lymphoma cells through mitochondrial damage

Taurine chloramine (TN-Cl) is one of the most abundant compounds generated by activated neutrophils. In contrast to HOCl, which causes necrosis, TN-Cl is a potent inducer of apoptosis in tumor cells. Here we show that the apoptosis induced by TN-Cl in human B lymphoma cells is dependent upon oxidant-mediated mitochondrial damage, a decrease in mitochondrial membrane potential, and caspase-9 activation. Further, we show that TN-Cl is taken up into the cells and is concentrated in the mitochondria, where it induces opening of the permeability transition pore and mitochondrial swelling. Identical activity is seen upon treatment of isolated mitochondria with TN-Cl and is blocked by the permeability transition pore inhibitors bongkrekic acid and cyclosporin A, as well as by the sulfhydryl-reducing agent tris(2-carboxyethyl)-phosphine. The data suggest that TN-Cl causes apoptosis through direct damage to the mitochondria.

Preparation of purified lymphoma cells suitable for therapy

BACKGROUND

Very few tumoral Ags have yet been isolated in NHL B cells. It is nevertheless possible to use whole tumor cells as a source of tumor Ags. We describe the purification of large numbers of human NHL B cells directly from lymph node or spleen biopsies, and different preparations allowing their use in a clinical setting.

METHODS

The purification procedure consists of the negative selection of tumor B cells: cells to be eliminated are opsonized by CD2 Abs, and then coupled to magnetic beads for separation by the Isolex 300 magnetic separator.

RESULTS

The mean yield of the purification was 74% for CD19+ cells, with a mean purity of 87%, dependent on the initial fraction of tumor cells in the biopsy. Using this procedure, a large number of purified tumor cells can be recovered from a biopsy in sterile conditions. We also describe treatments of B cells that can enhance their uptake by APCs, a critical step in anti-tumor immunotherapy strategies. Cells were opsonized by rituximab, or induced in apoptosis by irradiation, or necrosis by heating. Cell lysates were directly prepared from purified tumor cells.

DISCUSSION

These procedures were reproducible on every lymphoma cell, and treated cells were phagocytosed by APCs. The methodology described here allows the evaluation of the immunological potential of apoptotic, necrotic, opsonized lymphoma cells, or their lysates, in a clinical setting.

TLRs govern neutrophil activity in aspergillosis

Polymorphonuclear neutrophils (PMNs) are essential in initiation and execution of the acute inflammatory response and subsequent resolution of fungal infection. PMNs, however, may act as double-edged swords, as the excessive release of oxidants and proteases may be responsible for injury to organs and fungal sepsis. To identify regulatory mechanisms that may balance PMN-dependent protection and immunopathology in fungal infections, the involvement of different TLR-activation pathways was evaluated on human PMNs exposed to the fungus Aspergillus fumigatus. Recognition of Aspergillus and activation of PMNs occurred through the involvement of distinct members of the TLR family, each likely activating specialized antifungal effector functions. By affecting the balance between fungicidal oxidative and nonoxidative mechanisms, pro- and anti-inflammatory cytokine production, and apoptosis vs necrosis, the different TLRs ultimately impacted on the quality of microbicidal activity and inflammatory pathology. Signaling through TLR2 promoted the fungicidal activity of PMNs through oxidative pathways involving extracellular release of gelatinases and proinflammatory cytokines while TLR4 favored the oxidative pathways through the participation of azurophil, myeloperoxidase-positive, granules and IL-10. This translated in vivo in the occurrence of different patterns of fungal clearance and inflammatory pathology. Both pathways were variably affected by signaling through TLR3, TLR5, TLR6, TLR7, TLR8, and TLR9. The ability of selected individual TLRs to restore antifungal functions in defective PMNs suggests that the coordinated outputs of activation of multiple TLRs may contribute to PMN function in aspergillosis.

Liposomal amphotericin B activates antifungal resistance with reduced toxicity by diverting Toll-like receptor signalling from TLR-2 to TLR-4

OBJECTIVES

Neutrophils play a crucial role in the control of the Aspergillus fumigatus infection and act in concert with antifungal drugs. This study was undertaken to obtain insights into the possible involvement of Toll-like receptors (TLRs) in the interaction of liposomal amphotericin B (L-AmB; AmBisome) with neutrophils in response to A. fumigatus.

METHODS

For generation of bone marrow-transplanted mice, irradiated C57BL6 mice were infused with T cell-depleted allogeneic donor cells. For infection, mice were injected intranasally with Aspergillus fumigatus conidia and treated with L-Amb and deoxycholate amphotericin B prophylactically or therapeutically. For TLR-dependent antifungal functions, murine neutrophils were preincubated with antifungals or TLR ligands before the addition of Aspergillus conidia.

RESULTS

The results show that: (a) neutrophil activation by Aspergillus occurs through TLR signalling pathways differently affecting the oxidative and non-oxidative mechanisms of the killing machinery; (b) by diverting signalling from TLR-2 to TLR-4, liposomes of AmBisome activate neutrophils to an antifungal state while attenuating the pro-inflammatory effects of deoxycholate amphotericin B; (c) this translates in vivo to the optimization of the AmBisome therapeutic efficacy in mice with aspergillosis.

CONCLUSIONS

These results provide a putative molecular basis for the reduced infusion-related toxicity of AmBisome and suggest that TLR manipulation in vivo is amenable to the induction of optimal microbicidal activity in the absence of inflammatory cytotoxicity to host cells.

The macrophage and the apoptotic cell: an innate immune interaction viewed simplistically?

Macrophages play important roles in the clearance of dying and dead cells. Typically, and perhaps simplistically, they are viewed as the professional phagocytes of apoptotic cells. Clearance by macrophages of cells undergoing apoptosis is a non-phlogistic phenomenon which is often associated with actively anti-inflammatory phagocyte responses. By contrast, macrophage responses to necrotic cells, including secondarily necrotic cells derived from uncleared apoptotic cells, are perceived as proinflammatory. Indeed, persistence of apoptotic cells as a result of defective apoptotic-cell clearance has been found to be associated with the pathogenesis of autoimmune disease. Here we review the mechanisms by which macrophages interact with, and respond to, apoptotic cells. We suggest that macrophages are especially important in clearing cells at sites of histologically visible, high-rate apoptosis and that, otherwise, apoptotic cells are removed largely by non-macrophage neighbours. We challenge the view that necrotic cells, including persistent apoptotic cells are, of necessity, proinflammatory and immunostimulatory and suggest that, under appropriate circumstances, persistent apoptotic cells can provide a prolonged anti-inflammatory stimulus.

Phagocytosis of apoptotic cells and the resolution of inflammation

Clearance of apoptotic cells by phagocytic cells plays a significant role in the resolution of inflammation, protecting tissue from harmful exposure to the inflammatory and immunogenic contents of dying cells. Apoptosis induces cell surface changes that are important for recognition and engulfment of cells by phagocytes. These changes include alterations in surface sugars, externalization of phosphatidylserine and qualitative changes in the adhesion molecule ICAM-3. Several studies have contributed to clarify the role of the receptors on the surface of phagocytes that are involved in apoptotic cell clearance. The phagocytic removal of apoptotic cells does not elicit pro-inflammatory responses; in contrast, apoptotic cell engulfment appears to activate signals that suppress release of pro-inflammatory cytokines. Therefore, clearance of apoptotic leucocytes is implicated in the resolution of inflammation and mounting evidence suggests that defective clearance of apoptotic cells contributes to inflammatory and autoimmune diseases. Defining the ligands on apoptotic cells and the corresponding receptors on phagocytes with which they engage, is likely to lead to the development of novel anti-inflammatory pro-resolution drugs. In this article, we will review the recognition and signaling mechanisms involved in the phagocytosis of apoptotic cells as well as the role of endogenous compounds that play a relevant role in the modulation of inflammation. We will also discuss what is currently known about diseases that may reflect impaired phagocytosis and the consequences on inflammation and immune responses.

Lipid antioxidant, etoposide, inhibits phosphatidylserine externalization and macrophage clearance of apoptotic cells by preventing phosphatidylserine oxidation

Apoptosis is associated with the externalization of phosphatidylserine (PS) in the plasma membrane and subsequent recognition of PS by specific macrophage receptors. Selective oxidation of PS precedes its externalization/recognition and is essential for the PS-dependent engulfment of apoptotic cells. Because etoposide is a potent and selective lipid antioxidant that does not block thiol oxidation, we hypothesized that it may affect PS externalization/recognition without affecting other features of the apoptotic program. We demonstrate herein that etoposide induced apoptosis in HL-60 cells without the concomitant peroxidation of PS and other phospholipids. HL-60 cells also failed to externalize PS in response to etoposide treatment. In contrast, oxidant (H2O2)-induced apoptosis was accompanied by PS externalization and oxidation of different phospholipids, including PS. Etoposide potentiated H2O2-induced apoptosis but completely blocked H2O2-induced PS oxidation. Etoposide also inhibited PS externalization as well as phagocytosis of apoptotic cells by J774A.1 macrophages. Integration of exogenous PS or a mixture of PS with oxidized PS in etoposide-treated HL-60 cells reconstituted the recognition of these cells by macrophages. The current data demonstrate that lipid antioxidants, capable of preventing PS peroxidation, can block PS externalization and phagocytosis of apoptotic cells by macrophages and hence dissociate PS-dependent signaling from the final common pathway for apoptosis.

The danger hypothesis applied to idiosyncratic drug reactions

PURPOSE OF REVIEW

Idiosyncratic drug reactions pose a significant clinical threat and hamper drug development. The idiosyncratic nature of these reactions has made mechanistic studies exceedingly difficult, and yet without a better understanding of the mechanisms involved it is unlikely that much progress can be made in dealing with the problem. Several working hypotheses have been used to study these reactions, but none fits all of the characteristics that are observed. Borrowed from immunology, the danger hypothesis has most recently been used to explain several characteristics of these reactions. The present review describes the danger hypothesis and compares it with previous hypotheses to determine how well each fits with the observed characteristics of the reactions.

RECENT FINDINGS

Slow progress in the field continues and it is important to use new observations, such as identifying T cells that recognize drugs in the absence of reactive metabolite formation, to test and refine the working hypotheses. However, the development of animal models of idiosyncratic drug reactions as well as progress in basic immunology and genomics are likely to accelerate progress in this area in the near future.

SUMMARY

No one model fits the characteristics of all idiosyncratic drug reactions; however, the danger model provides a new perspective and suggests avenues of research that have the potential to increase our ability to predict and prevent such reactions significantly.

Cytotoxicity of inorganic mercury in murine T and B lymphoma cell lines: involvement of reactive oxygen species, Ca(2+) homeostasis, and cytokine gene expression

Mercury is a highly toxic heavy metal; exposure to mercury in humans and animals causes damage in several organs or systems including the immune system. To characterize the toxicity of mercury in the immune cells, the cytotoxic effects of inorganic mercury were studied in two distinct lymphoma lines, the murine T lymphoma (EL4) and B lymphoma (A20) cells. Mercury concentration-dependently decreased cell viability, membrane integrity, and proliferation in both EL4 and A20 cells. Mercury increased the reactive oxygen species (ROS) production in both EL4 and A20 cells, and pretreatment with antioxidants reversed mercury-induced ROS generation. Pretreatment of cells with antioxidants N-acetylcysteine (NAC) and silymarin decreased mercury-induced lactate dehydrogenase (LDH) release in both types of cells; however, Ca(2+) channel blocker lanthanum (La(2+)) decreased it only in A20 cells. The mode of cytotoxicity was a mixture of both apoptosis and necrosis. Mercury-induced apoptosis and necrosis in the two cell lines were indicated by staining with Hoechst 33258, propidium iodide, and co-staining with annexin V and propidium iodide. Both mercury-induced apoptosis and necrosis were attenuated by antioxidants. Mercury increased gene expression of IL-4 and TNFalpha in EL4 cells; these cytokines were not expressed in A20 cells. Data suggested different pathways of mercury-induced cytotoxicity in T and B lymphoma cells and involvement of ROS, Ca(2+) homeostasis, and inflammatory cytokine gene expression.

Appetizing rancidity of apoptotic cells for macrophages: oxidation, externalization, and recognition of phosphatidylserine

Programmed cell death (apoptosis) functions as a mechanism to eliminate unwanted or irreparably damaged cells ultimately leading to their orderly phagocytosis in the absence of calamitous inflammatory responses. Recent studies have demonstrated that the generation of free radical intermediates and subsequent oxidative stress are implicated as part of the apoptotic execution process. Oxidative stress may simply be an unavoidable yet trivial byproduct of the apoptotic machinery; alternatively, intermediates or products of oxidative stress may act as essential signals for the execution of the apoptotic program. This review is focused on the specific role of oxidative stress in apoptotic signaling, which is realized via phosphatidylserine-dependent pathways leading to recognition of apoptotic cells and their effective clearance. In particular, the mechanisms involved in selective phosphatidylserine oxidation in the plasma membrane during apoptosis and its association with disturbances of phospholipid asymmetry leading to phosphatidylserine externalization and recognition by macrophage receptors are at the center of our discussion. The putative importance of this oxidative phosphatidylserine signaling in lung physiology and disease are also discussed.

CD14-dependent clearance of apoptotic cells by human macrophages: the role of phosphatidylserine

Apoptotic-cell clearance is dependent on several macrophage surface molecules, including CD14. Phosphatidylserine (PS) becomes externalised during apoptosis and participates in the clearance process through its ability to bind to a novel receptor, PS-R. CD14 has the proven ability to bind phospholipids and may function as an alternative receptor for the externalised PS of apoptotic cells. Here we demonstrate that CD14 does not function preferentially as a PS receptor in apoptotic-cell clearance. Compared with phosphatidylcholine and phosphatidylethanolamine, PS was the least active phospholipid binding to human monocyte-derived macrophages and showed no specificity for soluble or membrane-anchored CD14. Significantly, PS-containing liposomes failed to inhibit CD14-dependent uptake of apoptotic cells by macrophages. PS exposure was, however, found to be insufficient for either CD14-dependent or CD14-independent apoptotic-cell uptake by phagocytes. The additional features that enable apoptotic-cell clearance are derived from mechanisms that can be divorced temporally from those responsible for the morphological features of apoptosis.

Serum-derived protein S binds to phosphatidylserine and stimulates the phagocytosis of apoptotic cells

Rapid phagocytosis of apoptotic cells is thought to limit the development of inflammation and autoimmune disease. Serum enhances macrophage phagocytosis of apoptotic cells. Here we identified protein S as the factor responsible for serum-stimulated phagocytosis of apoptotic cells. Protein S is best known for its anti-thrombotic activity, serving as a cofactor for protein C. Purified protein S was equivalent to serum in its ability to stimulate macrophage phagocytosis of apoptotic lymphoma cells, and immunodepletion of protein S eliminated the prophagocytic activity of serum. Protein S acted by binding to phosphatidylserine expressed on the apoptotic cell surface. Protein S is thus a multifunctional protein that can facilitate clearance of early apoptotic cells in addition to regulating blood coagulation.