Lysophosphatides enhance superoxide responses of stimulated human neutrophils

Structural basis for ligand recognition and signaling of the lysophosphatidylserine receptors GPR34 and GPR174

Lysophosphatidylserine (LysoPS) is a naturally occurring lipid mediator involved in various physiological and pathological processes especially those related to the immune system. GPR34, GPR174, and P2Y10 have been identified as the receptors for LysoPS, and its analogues have been developed as agonists or antagonists for these receptors. However, the lack of structural information hinders the drug development with novel characteristics, such as nonlipid ligands and allosteric modulators. Here, we determined the structures of human GPR34 and GPR174 in complex with LysoPS and G protein by cryo-EM. Combined with structural analysis and functional studies, we elucidated the lipid-binding modes of these receptors. By structural comparison, we identified the structural features of GPR34 and GPR174 in active state. Taken together, our findings provide insights into ligand recognition and signaling of LysoPS receptors and will facilitate the development of novel therapeutics for related inflammatory diseases and autoimmune diseases.

A Novel Hypothetical Approach to Explain the Mechanisms of Pathogenicity of Rheumatic Arthritis

The autoimmune disorder rheumatoid arthritis (RA) is a relapsing and chronic inflammatory disease that affects the synovial cells, cartilage, bone, and muscle. It is characterised by the accumulation of huge numbers of polymorphonuclear neutrophils (PMNs) and macrophages in the synovia. Auto-antibodies are deposited in the joint via the activity of highly cationic histones released from neutrophil extracellular traps (NETs) in a phenomenon termed NETosis. The cationic histones function as opsonic agents that bind to negatively charged domains in autoantibodies and complement compounds via strong electrostatic forces, facilitating their deposition and endocytosis by synovial cells. However, eventually the main cause of tissue damage is the plethora of toxic pro-inflammatory substances released by activated neutrophils recruited by cytokines. Tissue damage in RA can also be accompanied by infections which, upon bacteriolysis, release cell-wall components that are toxic to tissues. Some amelioration of the damaged cells and tissues in RA may be achieved by the use of highly anionic heparins, which can neutralize cationic histone activity, provided that these polyanions are co-administrated with anti-inflammatory drugs such as steroids, colchicine, or methotrexate, low molecular weight antioxidants, proteinase inhibitors, and phospholipase A2 inhibitors.

Lysophosphatidylinositol, an Endogenous Ligand for G Protein-Coupled Receptor 55, Has Anti-inflammatory Effects in Cultured Microglia

Lysophosphatidylinositol (LysoPI), an endogenous ligand for G protein-coupled receptor (GPR) 55, has been known to show various functions in several tissues and cells; however, its roles in the central nervous system (CNS) are not well known. In particular, the detailed effects of LysoPI on microglial inflammatory responses remain unknown. Microglia is the immune cell that has important functions in maintaining immune homeostasis of the CNS. In this study, we explored the effects of LysoPI on inflammatory responses using the mouse microglial cell line BV-2, which was stimulated with lipopolysaccharide (LPS), and some results were confirmed also in rat primary microglia. LysoPI was found to reduce LPS-induced nitric oxide (NO) production and inducible NO synthase protein expression without affecting cell viability in BV-2 cells. LysoPI also suppressed intracellular generation of reactive oxygen species both in BV-2 cells and primary microglia and cytokine release in BV-2 cells. In addition, LysoPI treatment decreased phagocytic activity of LPS-stimulated BV-2 cells and primary microglia. The GPR55 antagonist CID16020046 completely inhibited LysoPI-induced downregulation of phagocytosis in BV-2 microglia, but did not affect the LysoPI-induced decrease in NO production. Our results suggest that LysoPI suppresses microglial phagocytosis via a GPR55-dependent pathway and NO production via a GPR55-independent pathway. LysoPI may contribute to neuroprotection in pathological conditions such as brain injury or neurodegenerative diseases, through its suppressive role in the microglial inflammatory response.

An Updated Review of Pro- and Anti-Inflammatory Properties of Plasma Lysophosphatidylcholines in the Vascular System

Lysophosphatidylcholines are a group of bioactive lipids heavily investigated in the context of inflammation and atherosclerosis development. While present in plasma during physiological conditions, their concentration can drastically increase in certain inflammatory states. Lysophosphatidylcholines are widely regarded as potent pro-inflammatory and deleterious mediators, but an increasing number of more recent studies show multiple beneficial properties under various pathological conditions. Many of the discrepancies in the published studies are due to the investigation of different species or mixtures of lysophatidylcholines and the use of supra-physiological concentrations in the absence of serum or other carrier proteins. Furthermore, interpretation of the results is complicated by the rapid metabolism of lysophosphatidylcholine (LPC) in cells and tissues to pro-inflammatory lysophosphatidic acid. Interestingly, most of the recent studies, in contrast to older studies, found lower LPC plasma levels associated with unfavorable disease outcomes. Being the most abundant lysophospholipid in plasma, it is of utmost importance to understand its physiological functions and shed light on the discordant literature connected to its research. LPCs should be recognized as important homeostatic mediators involved in all stages of vascular inflammation. In this review, we want to point out potential pro- and anti-inflammatory activities of lysophospholipids in the vascular system and highlight recent discoveries about the effect of lysophosphatidylcholines on immune cells at the endothelial vascular interface. We will also look at their potential clinical application as biomarkers.

Pro-inflammatory agents released by pathogens, dying host cells, and neutrophils act synergistically to destroy host tissues: a working hypothesis

We postulate that the extensive cell and tissue damage inflicted by many infectious, inflammatory and post-inflammatory episodes is an enled result of a synergism among the invading microbial agents, host neutrophils and dead and dying cells in the nidus. Microbial toxins and other metabolites along with the plethora of pro-inflammatory agents released from activated neutrophils massively recruited to the infectious sites and high levels of cationic histones, other cationic peptides, proteinases and Th1 cytokines released from activated polymorphonuclear neutrophils (PMNs) and from necrotized tissues may act in concert (synergism) to bring about cell killing and tissue destruction. Multiple, diverse interactions among the many potential pro-inflammatory moieties have been described in these complex lesions. Such infections are often seen in the skin and aerodigestive tract where the tissue is exposed to the environment, but can occur in any tissue. Commonly, the tissue-destructive infections are caused by group A streptococci, pneumococci, Staphylococcus aureus, meningococci, Escherichia coli and Shigella, although many other microbial species are seen on occasion. All these microbial agents are characterized by their ability to recruit large numbers of PMNs. Given the complex nature of the disease process, it is proposed that, to treat these multifactorial disorders, a "cocktail" of anti-inflammatory agents combined with non-bacteriolytic antibiotics and measures to counteract the critical toxic role of cationic moieties might prove more effective than a strategy based on attacking the bacteria alone.

Exploring the Inflammatory Metabolomic Profile to Predict Response to TNF-α Inhibitors in Rheumatoid Arthritis

In clinical practice, approximately one-third of patients with rheumatoid arthritis (RA) respond insufficiently to TNF-α inhibitors (TNFis). The aim of the study was to explore the use of a metabolomics to identify predictors for the outcome of TNFi therapy, and study the metabolomic fingerprint in active RA irrespective of patients’ response. In the metabolomic profiling, lipids, oxylipins, and amines were measured in serum samples of RA patients from the observational BiOCURA cohort, before start of biological treatment. Multivariable logistic regression models were established to identify predictors for good- and non-response in patients receiving TNFi (n = 124). The added value of metabolites over prediction using clinical parameters only was determined by comparing the area under receiver operating characteristic curve (AUC-ROC), sensitivity, specificity, positive- and negative predictive value and by the net reclassification index (NRI). The models were further validated by 10-fold cross validation and tested on the complete TNFi treatment cohort including moderate responders. Additionally, metabolites were identified that cross-sectionally associated with the RA disease activity score based on a 28-joint count (DAS28), erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP). Out of 139 metabolites, the best-performing predictors were sn1-LPC(18:3-ω3/ω6), sn1-LPC(15:0), ethanolamine, and lysine. The model that combined the selected metabolites with clinical parameters showed a significant larger AUC-ROC than that of the model containing only clinical parameters (p = 0.01). The combined model was able to discriminate good- and non-responders with good accuracy and to reclassify non-responders with an improvement of 30% (total NRI = 0.23) and showed a prediction error of 0.27. For the complete TNFi cohort, the NRI was 0.22. In addition, 88 metabolites were associated with DAS28, ESR or CRP (p<0.05). Our study established an accurate prediction model for response to TNFi therapy, containing metabolites and clinical parameters. Associations between metabolites and disease activity may help elucidate additional pathologic mechanisms behind RA.

A revisited hemolytic assay for palytoxin detection: Limitations for its quantitation in mussels

Palytoxin (PLTX) and its analogues have been detected as seafood contaminants associated with a series of human foodborne poisonings. Due to a number of fatalities ascribed to the ingestion of PLTX-contaminated marine organisms, the development of methods for its detection in seafood has been recommended by the European Food Safety Authority (EFSA). Due to its feasibility, the spectrophotometric hemolytic assay is widely used to detect PLTX in different matrices, even though a standardized protocol is still lacking. Thus, on the basis of available assay procedures, a new standardized protocol was set up using purified human erythrocytes exposed to PLTX (working range: 3.9 × 10(-10)-2.5 × 10(-8) M) in a K(+)-free phosphate buffered saline solution, employing a 5 h incubation at 41 °C. An intra-laboratory characterization demonstrated its sensitivity (limit of detection, LOD = 1.4 × 10(-10) M and quantitation, LOQ = 3.4 × 10(-10) M), accuracy (bias = -0.8%), repeatability (RSDr = 15% and 6% for intra- and inter-day repeatability, respectively) and specificity. However, the standardized method seems not to be suitable for PLTX quantitation in complex matrices, such as mussel (Mytilus galloprovincialis) extracts, at least below the limit suggested by EFSA (30 μg PLTXs/Kg shellfish meat). Thus, the hemolytic assay for PLTX quantitation in seafood should be used only after a careful evaluation of the specific matrix effects.

Phox activity of differentiated PLB-985 cells is enhanced, in an agonist specific manner, by the PLA2 activity of Prdx6-PLA2

Peroxiredoxin 6-phospholipase A(2) (Prdx6-PLA(2) ) is a bi-functional enzyme with peroxi-redoxin (Prdx) and phospholipase A(2) (PLA(2) ) activities. To investigate its impact on phagocyte NADPH oxidase (phox) activity in a neutrophil model, the protein was knocked down in PLB-985 cells using stable expression of a small hairpin RNA (shRNA) and phox activity was monitored after cell differentiation. The knockdown cells had reduced oxidase activity in response to stimulation with the formylated peptide fMLF, but the response to the phorbol ester PMA was unchanged. Reintroduction of shRNA-resistant Prdx6-PLA(2) into the knockdown cells by stable transfection with a Prdx6-PLA(2) expression plasmid restored the fMLF response, as did reintroduction of Prdx6-PLA(2) mutated in the Prdx active site; reintroduction of PLA(2) active site mutants, however, failed to restore the response. Thus, the PLA(2) activity of Prdx6-PLA(2) in intact cells mediates its ability to enhance phox activity in response to fMLF. In combination with previous publications by other groups, our work indicates that various PLA(2) isoforms can enhance oxidase activity but they are differentially important in different cell types and in the response to different agonists.

Emerging roles for lysophosphatidylserine in resolution of inflammation

Despite overlapping structural aspects with other phospholipids, lysophosphatidylserine (lysoPS), the monoacyl derivative of phosphatidylserine (diacylPS), appears to exert unique signaling characteristics important in both the early stages of initiating acute inflammation and in the orchestration of its resolution. LysoPS has long been known as a signaling phospholipid in mast cell biology, markedly enhancing stimulated histamine release and eicosanoid production. More recently, there has been a resurgence of interest in lysoPS as new roles in the promotion of phagocytosis of apoptotic cells, so-called efferocytosis, and resolution of inflammation have been identified. With regard to the latter, lysoPS generated in/on activated or aged apoptotic neutrophils enhances their clearance by macrophages via signaling through the macrophage G-protein coupled receptor G2A. In macrophages, this early acting pathway results in PKA-dependent augmentation of Rac1 activity via increased production of PGE₂ and cAMP. As such, macrophages stimulated with lysoPS demonstrate significantly increased efferocytic capacity necessary to clear large numbers of recruited neutrophils typical of acute inflammation. Given that clearance of these cells is critical for restoration of tissue function, lysoPS, as a pro-resolving lipid mediator, is hypothesized to play a key role in promoting timely resolution of inflammation. This article will review our current knowledge of lysoPS biology including receptor signaling and mechanisms of generation as well as summarize the more recent evidence of its expanding roles in inflammation.

Lysophosphatidylcholine as an adjuvant for lentiviral vector mediated gene transfer to airway epithelium: effect of acyl chain length

BACKGROUND

Poor gene transfer efficiency has been a major problem in developing an effective gene therapy for cystic fibrosis (CF) airway disease. Lysophosphatidylcholine (LPC), a natural airway surfactant, can enhance viral gene transfer in animal models. We examined the electrophysiological and physical effect of airway pre-treatment with variants of LPC on lentiviral (LV) vector gene transfer efficiency in murine nasal airways in vivo.

METHODS

Gene transfer was assessed after 1 week following nasal instillations of a VSV-G pseudotype LV vector pre-treated with a low and high dose of LPC variants. The electrophysiological effects of a range of LPC variants were assessed by nasal transepithelial potential difference measurements (TPD) to determine tight junction permeability. Any physical changes to the epithelium from administration of the LPC variants were noted by histological methods in airway tissue harvested after 1 hour.

RESULTS

Gene transduction was significantly greater compared to control (PBS) for our standard LPC (palmitoyl/stearoyl mixture) treatment and for the majority of the other LPC variants with longer acyl chain lengths. The LPC variant heptadecanoyl also produced significantly greater LV gene transfer compared to our standard LPC mixture. LV gene transfer and the transepithelial depolarization produced by the 0.1% LPC variants at 1 hour were strongly correlated (r2 = 0.94), but at the 1% concentration the correlation was less strong (r2 = 0.59). LPC variants that displayed minor to moderate levels of disruption to the airway epithelium were clearly associated with higher LV gene transfer.

CONCLUSIONS

These findings show the LPC variants effect on airway barrier function and their correlation to the effectiveness of gene expression. The enhanced expression produced by a number of LPC variants should provide new options for preclinical development of efficient airway gene transfer techniques.

Lysophospholipids of Different Classes Mobilize Neutrophil Secretory Vesicles and Induce Redundant Signaling through G2A

Lysophosphatidylcholine has been shown to enhance neutrophil functions through a mechanism involving the G protein-coupled receptor G2A. Recent data support an indirect effect of lysophosphatidylcholine on G2A rather than direct ligand binding. These observations prompted the hypothesis that other lysophospholipids (lyso-PLs) may also signal for human neutrophil activation through G2A. To this end, 1-oleoyl-2-hydroxy-sn-glycero-3-[phospho-L-choline], but also C18:1/OH lyso-PLs bearing the phosphoserine and phosphoethanolamine head groups, presented on albumin, were shown to signal for calcium flux in a self- and cross-desensitizing manner, implicating a single receptor. Blocking Abs to G2A inhibited calcium signaling by all three lyso-PLs. Furthermore, inhibition by both pertussis toxin and U-73122 established signaling via the Galphai/phospholipase C pathway for calcium mobilization. Altered plasma membrane localization of G2A has been hypothesized to facilitate signaling. Accordingly, an increase in detectable G2A was demonstrated by 1 min after lyso-PL stimulation and was followed by visible patching of the receptor. Western blotting showed that G2A resides in the plasma membrane/secretory vesicle fraction and not in neutrophil primary, secondary, or tertiary granules. Enhanced detection of G2A induced by lyso-PLs was paralleled by enhanced detection of CD45, confirming mobilization of the labile secretory vesicle pool. Together, these data show that lyso-PLs bearing various head groups redundantly mobilize G2A latent within secretory vesicles and result in G2A receptor/Galphai/phospholipase C signaling for calcium flux in neutrophils.

Lysophosphatidylcholine modulates neutrophil oxidant production through elevation of cyclic AMP

Lysophosphatidylcholine (LPC) is an oxidized phospholipid present in micromolar concentrations in blood and inflamed tissues. The effects of LPC on neutrophil functions remain incompletely understood, because conflicting reports exist for its stimulatory and inhibitory roles. We report in this study that LPC inhibits superoxide generation in fMLP- and PMA-stimulated neutrophils without affecting fMLP-induced Ca(2+) mobilization and cell viability. This effect was observed with LPC dissolved in ethanol, but not with LPC stock solutions prepared in water or in BSA-containing aqueous solution with sonication. Under the same experimental conditions, platelet-activating factor primed neutrophils for superoxide generation. The inhibitory effect of LPC was observed within 30 s after its application and was maximal at LPC concentrations between 0.1 and 1 muM. Inhibition of superoxide generation was accompanied by a 2.5-fold increase in the intracellular cAMP concentration. In addition, LPC reduced fMLP-stimulated phosphorylation of ERK and Akt and membrane translocation of p67(phox) and p47(phox). The protein kinase A inhibitors H-89 and adenosine 3'5'-cyclic monophosphorothioate Rp-isomer (Rp-cAMP) partially restored superoxide production in LPC-treated neutrophils, indicating involvement of protein kinase A in LPC-mediated inhibition. Using an ex vivo mouse lung perfusion model that measures lung weight change and capillary filtration coefficient, we found that LPC prevented lung vascular injury mediated by fMLP-activated neutrophils. Taken together, these results suggest that LPC-induced elevation of intracellular cAMP is partially responsible for its inhibition of neutrophil NADPH oxidase activation. A similar mechanism of inhibition may be used for the control of neutrophil-mediated tissue injury.

Potential mechanisms for the enhancement of HERG K+ channel function by phospholipid metabolites

1. Phospholipid metabolites lysophospholipids cause extracellular K(+) accumulation and action potential shortening with increased risk of arrhythmias during myocardial ischemia. Here we studied effects of several lysophospholipids with different lengths of hydrocarbon chains and charged headgroups on HERG K(+) currents (I(HERG)) expressed in HEK293 cells and the potential mechanisms using whole-cell patch-clamp techniques. 2. Only the lipids with 16 hydrocarbons such as 1-palmitoyl-lysophosphatidylcholine (LPC-16) and 1-palmitoyl-lysophosphatidylglycerol (LPG-16) were found to produce significant enhancement of I(HERG) and negative shifts of HERG activation, although the voltage dependence of the effects was different between LPC-16 and LPG-16 which have differently charged headgroups. The lipid with 18 hydrocarbons modestly increased I(HERG). The lipids with 6 or 24 hydrocarbons had no effect or slightly decreased I(HERG). 3. Inhibition or activation of protein kinase C did not alter the effects of LPC-16 and LPG-16. Participation of phosphatidylinositol-4,5-bisphosphate in I(HERG) enhancement by LPC-16/LPG-16 was also excluded. 4. Vitamin E augmented the effects of LPC-16/LPG-16 whereas xanthine/xanthine oxidase reduced I(HERG): indicating that LPC-16/LPG-16 produced dual effects on I(HERG): direct enhancement of I(HERG) and indirect suppression via production of superoxide anion. 5. We conclude that enhancement of HERG function by lysophospholipids is specific to the lipids with 16-hydrocarbon chain structure and the pattern of voltage dependence is determined by the polar headgroups. The increase in I(HERG) is best described by direct interactions between lipid molecules and HERG proteins, which is consistent with lack of effects via membrane destabilization or modulation by intracellular signaling pathways.

Identification of 1-lysophosphatidylethanolamine (C(16:1)) as an antimicrobial compound in the housefly, Musca domestica

We observed that a methanolic whole body extract of uninfected last instar larvae of the housefly, Musca domestica, displayed antifungal and antibacterial activity. We have further purified this extract to a single active fraction using reversed phase high performance liquid chromatography. The pure fraction inhibited growth of the Gram-positive bacteria Bacillus thuringiensis and the yeast Saccharomyces cerevisiae, but not the Gram-negative bacteria Escherichia coli. The active compound was determined to have a molecular mass of 451.2 Da. Further analysis by nuclear magnetic resonance identified the substance as mono-unsaturated 1-lysophosphatidylethanolamine (C(16:1)) (1-LPE). The structurally different and more common 2-LPE have been described as mediators of the antimicrobial activity of rimenophenazine antibiotic agents (Van Rensburg et al., 1992). Our results suggest that the isolated 1-LPE displays a higher activity in comparison, possibly based on structure-specific differences in activity.

Lysophosphatidylcholines prime the NADPH oxidase and stimulate multiple neutrophil functions through changes in cytosolic calcium

A mixture of lysophosphatidylcholines (lyso-PCs) are generated during blood storage and are etiologic in models of acute lung injury. We hypothesize that lyso-PCs stimulate polymorphonuclear neutrophils (PMNs) through Ca(2)(+)-dependent signaling. The lyso-PC mix (0.45-14.5 micro M) and the individual lyso-PCs primed formyl-Met-Leu-Phe (fMLP) activation of the oxidase (1.8- to 15.7-fold and 1.7- to 14.8-fold; P<0.05). Labeled lyso-PCs demonstrated a membrane association with PMNs and caused rapid increases in cytosolic Ca(2)(+). Receptor desensitization studies implicated a common receptor or a family of receptors for the observed lyso-PC-mediated changes in PMN priming, and cytosolic Ca(2)(+) functions were pertussis toxin-sensitive. Lyso-PCs caused rapid serine phosphorylation of a 68-kD protein but did not activate mitogen-activated protein kinases or cause changes in tyrosine phosphorylation. With respect to alterations in PMN function, lyso-PCs caused PMN adherence, increased expression of CD11b and the fMLP receptor, reduced chemotaxis, provoked changes in morphology, elicited degranulation, and augmented fMLP-induced azurophilic degranulation (P<0.05). Cytosolic Ca(2)(+) chelation inhibited lyso-PC-mediated priming of the oxidase, CD11b surface expression, changes in PMN morphology, and serine phosphorylation of the 68-kD protein. In conclusion, lyso-PCs affect multiple PMN functions in a Ca(2)(+)-dependent manner that involves the activation of a pertussis toxin-sensitive G-protein.

A two-insult in vitro model of PMN-mediated pulmonary endothelial damage: requirements for adherence and chemokine release

Lysophosphatidylcholines (lyso-PCs), generated during blood storage, are etiologic in a two-insult, sepsis-based model of transfusion-related acute lung injury (TRALI). Individually, endotoxin (LPS) and lyso-PCs prime but do not activate neutrophils (PMNs). We hypothesized that priming of PMNs alters their reactivity such that a second priming agent causes PMN activation and endothelial cell damage. PMNs were primed or not with LPS and then treated with lyso-PCs, and oxidase activation and elastase release were measured. For coculture experiments, activation of human pulmonary microvascular endothelial cells (HMVECs) was assessed by ICAM-1 expression and chemokine release. HMVECs were stimulated or not with LPS, PMNs were added, cells were incubated with lyso-PCs, and the number of viable HMVECs was counted. Lyso-PCs activated LPS-primed PMNs. HMVEC activation resulted in increased ICAM-1 and release of ENA-78, GRO alpha, and IL-8. PMN-mediated HMVEC damage was dependent on LPS activation of HMVECs, chemokine release, PMN adhesion, and lyso-PC activation of the oxidase. In conclusion, sequential exposure of PMNs to priming agents activates the microbicidal arsenal, and PMN-mediated HMVEC damage was the result of two insults: HMVEC activation and PMN oxidase assembly.

Effects of lysophospholipids on the generation of reactive oxygen species by fMLP- and PMA-stimulated human neutrophils

In this study, the effects of exogenous lysophospholipids--lysophosphatidic acid, lysophosphatidylcholine, lysophosphatidylethanolamine and lysophosphatidylserine--on the kinetics of reactive oxygen species (ROS) production by human neutrophils are described. The ROS production by human neutrophils was monitored by luminol-amplified chemiluminescence after cell stimulation with the chemotactic tripeptide, fMLP, or with the phorbol ester, PMA. The interaction of lysophospholipids with the membrane of human neutrophils was additionally tested by mass spectrometry. Lysophosphatidylcholine showed the most pronounced effect on the chemiluminescence pattern, as well as the intensity of the fMLP and PMA-stimulated cells, whereas lysophosphatidic acid showed a slight priming effect when fMLP was used for stimulation. In the case of fMLP-stimulated cells, lysophosphatidylcholine inhibited the first phase and enhanced the second phase of chemiluminescence, whereas the chemiluminescence of PMA-stimulated neutrophils was inhibited in a concentration-dependent manner. We conclude that lysophosphatidylcholine is able to interact with protein kinase C-dependent signalling pathways leading to NADPH oxidase activation.

Vitamin E attenuates the injurious effects of bioactive phospholipids on human ciliated epithelium in vitro

Bioactive phospholipids (PL), particularly lysophosphatidylcholine (LPC), are being increasingly implicated in the pathogenesis of various acute and chronic inflammatory disorders, particularly those of the airways, while there is emerging evidence that vitamin E may function as a natural antagonist of these lipid mediators of inflammation. The aims of this study were to document the effects of vitamin E on the inhibition of ciliary beating and damage to structural integrity of human ciliated epithelium induced by the PL, platelet-activating factor (PAF), lyso-PAF and LPC in vitro in relation to the anti-oxidative and membrane-stabilizing properties of the vitamin. Ciliary beat frequency was measured by a phototransistor technique, and damage to structural integrity assessed by a visual-scoring index, while superoxide production by polymorphonuclear leukocytes and membrane-stabilizing potential were measured using lucigenin-enhanced chemiluminescence and haemolytic procedures, respectively. All three PL caused inhibition of ciliary beating and structural damage to human ciliated epithelium by membrane-directed cytotoxic mechanisms, which were potentiated by human polymorphonuclear leukocytes due to induction of oxidant-mediated injury. Both direct and phagocyte-inflicted epithelial injury was attenuated by vitamin E. In haemolytic and chemiluminescence assays, vitamin E neutralized both the membrane-destabilizing and pro-oxidative actions of all three PL, while spectrophotometric analysis of mixtures of vitamin E with PAF, lyso-PAF and LPC revealed alterations in peak intensity, as well as peak shifts, indicative of physicochemical interactions between the vitamin and the PL. Vitamin E status may be a determinant of susceptibility to phospholipid-mediated airway inflammation and damage.

Detection of individual phospholipids in lipid mixtures by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: phosphatidylcholine prevents the detection of further species

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry is an established tool for the analysis of proteins, whereas it gained by far less interest in the field of lipid analysis. This method works well with phospholipids as well as organic cell extracts and provides high sensitivity and reproducibility. The aim of the present paper is to extend our previous studies to the analysis of lysophospholipids and phospholipid mixtures. To study the suitability of MALDI-TOF mass spectrometry for the analysis of lysophospholipids, different phospholipids like phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidic acid, and phosphatidylinositol as well as their mixtures were digested with phospholipase A(2). Positive and negative ion mass spectra of all phospholipids before and after digestion were recorded. In all these cases, the molecular ions of the expected digestion products could be detected and only a very small extent of further fragmentation was observed. On the other hand, spectra of phospholipid mixtures containing phosphatidylcholine were strongly dominated by phosphatidylcholine and lysophosphatidylcholine signals, which prevented the detection of further phospholipids even if those lipids were present in comparable amounts. This is of paramount interest for the analysis of tissue and cell extracts.

Can we learn from the pathogenetic strategies of group A hemolytic streptococci how tissues are injured and organs fail in post-infectious and inflammatory sequelae?

The purpose of this review-hypothesis is to discuss the literature which had proposed the concept that the mechanisms by which infectious and inflammatory processes induce cell and tissue injury, in vivo, might paradoxically involve a deleterious synergistic 'cross-talk', among microbial- and host-derived pro-inflammatory agonists. This argument is based on studies of the mechanisms of tissue damage caused by catalase-negative group A hemolytic streptococci and also on a large body of evidence describing synergistic interactions among a multiplicity of agonists leading to cell and tissue damage in inflammatory and infectious processes. A very rapid cell damage (necrosis), accompanied by the release of large amounts of arachidonic acid and metabolites, could be induced when subtoxic amounts of oxidants (superoxide, oxidants generated by xanthine-xanthine oxidase, HOCl, NO), synergized with subtoxic amounts of a large series of membrane-perforating agents (streptococcal and other bacterial-derived hemolysins, phospholipases A2 and C, lysophosphatides, cationic proteins, fatty acids, xenobiotics, the attack complex of complement and certain cytokines). Subtoxic amounts of proteinases (elastase, cathepsin G, plasmin, trypsin) very dramatically further enhanced cell damage induced by combinations between oxidants and the membrane perforators. Thus, irrespective of the source of agonists, whether derived from microorganisms or from the hosts, a triad comprised of an oxidant, a membrane perforator, and a proteinase constitutes a potent cytolytic cocktail the activity of which may be further enhanced by certain cytokines. The role played by non-biodegradable microbial cell wall components (lipopolysaccharide, lipoteichoic acid, peptidoglycan) released following polycation- and antibiotic-induced bacteriolysis in the activation of macrophages to release oxidants, cytolytic cytokines and NO is also discussed in relation to the pathophysiology of granulomatous inflammation and sepsis. The recent failures to prevent septic shock by the administration of only single antagonists is disconcerting. It suggests, however, that since tissue damage in post-infectious syndromes is caused by synergistic interactions among a multiplicity of agents, only cocktails of appropriate antagonists, if administered at the early phase of infection and to patients at high risk, might prevent the development of post-infectious syndromes.

Lysophosphatidylcholine generates superoxide anions through activation of phosphatidylinositol 3-kinase in human neutrophils

Lysophosphatidylcholine (LPC) accumulates in inflammatory tissues, where neutrophils are recruited to generate superoxide anions (O2.-). Here, we show that LPC stimulates O2.- generation in human neutrophils and that the activity is inhibited with phosphatidylinositol 3-kinase (PI3 kinase) inhibitors, but not with protein kinase C (PKC) inhibitors. Furthermore, we demonstrate that LPC activates PI3 kinase in neutrophils. Thus, LPC might contribute to host defense by generating O2.- in neutrophils through PI3 kinase activation, but not through PKC activation.

Could synergistic interactions among reactive oxygen species, proteinases, membrane-perforating enzymes, hydrolases, microbial hemolysins and cytokines be the main cause of tissue damage in infectious and inflammatory conditions?

The mechanisms of cellular damage caused by infectious and inflammatory processes are complex and are still not fully understood. There is, however, a consensus that reactive oxygen species (ROS) generated by phagocytes migrating to injured tissues might be the main agents responsible for cellular damage in inflammatory processes. However, because both activated phagocytes and catalase-negative, peroxide-producing, toxigenic bacteria (Streptococci, Clostridiae) secrete a near-identical array of proinflammatory agonists, including reactive oxygen species (ROS), and because these microbial species might kill their targets by a synergism among several of their secreted enzymes (a multicomponent system), we postulated that activated phagocytes might also function in the same way. Using radiolabeled targets, in culture, we demonstrated that subtoxic amounts of a variety of oxidants (H2O2, radicals produced by xanthine-xanthine-oxidase, peroxyl radical, NO) acted synergistically with subtoxic amounts of a large series of membrane-perforating agents (microbial hemolysins, phospholipases, fatty acids, cationic proteins, proteinases, bile salts, the attack complex of complement, the xenobiotics, lindane, ethanol, methanol) to kill cells in culture and to release large amounts of arachidonic acid and metabolites. Membrane perforators might act primarily to overcome the potent antioxidant systems present in all mammalian cells and scavengers of ROS and inhibitors of the additional agonists might act to abolish the synergism among ROS and the membrane-damaging agents. It is also proposed that protection against tissue damage in vivo should also include 'cocktails' of appropriate antagonists. It is enigmatic that those publications which do describe both in-vitro and in-vivo models proposing that a synergism among a multiplicity of agonists might truly represent the mechanisms by which tissues are injured, in vivo, are hardly ever quoted in the current literature.

Diethyldithiocarbamate and nitric oxide synergize with oxidants and with membrane-damaging agents to injure mammalian cells

The effect of diethyldithiocarbamate (DDC) and sodium nitroprusside (SNP) on the killing of endothelial cells and on the release of arachidonate by mixtures of oxidants and membrane-damaging agents was studied in a tissue culture model employing bovine aortic endothelial cells labeled either with 51Chromium or 3arachidonic acid. While exposure to low, subtoxic concentrations of oxidants (reagent H2O2, glucose-oxidase generated peroxide, xanthine xanthine oxidase, AAPH-generated peroxyl radical, menadione-generated oxidants) did not result either in cell death or in the loss of membrane-associated arachidonic acid, the addition of subtoxic amounts of a variety of membrane-damaging agents (streptolysin S, PLA2, histone, taurocholate, wheatgerm agglutinin) resulted in a synergistic cell death. However, no significant amounts of arachidonate were released unless proteinases were also present. The addition to these reaction mixtures of subtoxic amounts of DDC (an SOD inhibitor and a copper chelator) not only very markedly enhanced cell death but also resulted in the release of large amounts of arachidonate (in the complete absence of added proteinases). Furthermore, the inclusion in DDC-containing reaction mixtures of subtoxic amounts of SNP, a generator of NO, further enhanced, in a synergistic manner, both cell killing and the release of arachidonate. Cell killing and the release of arachidonate induced by the DDC and SNP-containing mixtures of agonists were strongly inhibited by catalase, glutathione, N-acetyl cysteine, vitamin A, and by a nonpenetrating PLA2 inhibitor as well as by tetracyclines. A partial inhibition of cell killing was also obtained by 1,10-phenanthroline and by antimycin. It is suggested that DDC might amplify cell damage by forming intracellular, loosely-bound complexes with copper and probably also by depleting antioxidant thiols. It is also suggested that "cocktails" containing oxidants, membrane-damaging agents, DDC, and SNP might be beneficial for killing of tumor cells in vivo and for the assessment of the toxicity of xenobiotics in vitro.

Membrane-stabilizing, anti-inflammatory interactions of macrolides with human neutrophils

The effects of the macrolide antimicrobial agents azithromycin, clarithromycin, erythromycin and roxithromycin on the prooxidative activity of stimulated human neutrophils have been investigated in vitro. Superoxide generation by activated neutrophils was measured by lucigenin-enhanced chemiluminescence. At the concentrations used (2.5-80 micrograms/ml) none of the test agents was cytotoxic, nor did they possess superoxide-scavenging properties. Treatment of neutrophils with all 4 macrolides was accompanied by dose-related inhibition of superoxide production by cells activated with FMLP or the calcium ionophore (A23187), while the responses activated by phorbol myristate acetate (PMA) or opsonized zymosan were minimally affected. The anti-oxidative interactions of roxithromycin with FMLP-activated neutrophils were neutralized by pretreatment of the cells with low, non-cytotoxic concentrations (0.5 microgram/ml) of the prooxidative, proinflammatory bioactive phospholipids, lysophosphatidylcholine (LPC), platelet-activating factor (PAF) and lyso-PAF (LPAF). Using an assay of membrane-stabilizing activity, the macrolides antagonized the membrane-disruptive effects of LPC, PAF and LPAF, without affecting enzymes involved in their synthesis. These membrane-stabilizing interactions of macrolides with neutrophils may counteract the proinflammatory, prooxidative activity of several bioactive lipids which have been implicated in the pathogenesis of bronchial asthma.

Membrane stabilizing, anti-oxidative interactions of propranolol and dexpropranolol with neutrophils

We have investigated the effects of the beta-adrenoreceptor-blocking agent, propranolol (9-300 microM) on several pro-inflammatory activities of human neutrophils in vitro. Superoxide production by calcium ionophore (A23187)-activated neutrophils was particularly sensitive to inhibition by low concentrations (9-18.7 microM) of this drug. However, inhibition of superoxide generation by neutrophils activated with phorbol myristate acetate (PMA), opsonized zymosan (OZ), and arachidonate (AA) only occurred with higher concentrations of propranolol, and coincided with decreased intracellular calcium fluxes, phospholipase A2 (PLA2) activity and synthesis of platelet-activating factor (PAF). Propranolol possessed neither cytotoxic nor superoxide-scavenging properties but, using a haemolytic assay of membrane-stabilizing activity, this agent neutralized the membrane-disruptive effects of the bioactive phospholipids, lysophosphatidylcholine (LPC), PAF, and lysoPAF(LPAF). A mechanistic relationship between the anti-oxidative and membrane-stabilizing properties of propranolol was suggested by the observation that pretreatment of neutrophils with LPC or PAF eliminated the inhibitory effects of the drug on superoxide generation by PMA-activated neutrophils. Dexpropranolol, a stereoisomer with minimal beta-blocking activity, and propranolol were equally effective with respect to their membrane-stabilizing and anti-oxidative interactions with neutrophils, but several other beta-blocking agents (atenolol, metoprolol, sotalol, and timolol) did not possess these activities. Inhibition of oxidant generation is, therefore, not a common property of beta-blocking agents and, in the case of propranolol, appears to occur as a consequence of membrane-stabilization rather than by beta-receptor-directed effects.

Anti-inflammatory, membrane-stabilizing interactions of salmeterol with human neutrophils in vitro

1. We have investigated the effects of salmeterol (0.3-50 microM) on several pro-inflammatory activities of human neutrophils in vitro. 2. Oxidant production by FMLP- and calcium ionophore (A23187)-activated neutrophils was particularly sensitive to inhibition by low concentrations (0.3-3 microM) of salmeterol, while the responses of phorbol myristate acetate- and opsonised zymosan-stimulated cells were affected only by higher concentrations (3-50 microM) of the drug. At these concentrations salmeterol is not cytotoxic, nor does it act as a scavenger of superoxide. 3. These anti-oxidative interactions of salmeterol with neutrophils were insensitive to propranolol but could be eliminated by washing the cells, or by pretreatment with low concentrations (1-2 microM) of the pro-oxidative, membrane-destabilizing phospholipids, lysophosphatidylcholine (LPC), platelet activating factor (PAF) and lysoPAF (LPAF). 4. At concentrations of 6.25-50 microM salmeterol interfered with several other activities of stimulated neutrophils, including intracellular calcium fluxes, phospholipase A2 activity and synthesis of PAF. 5. In an assay of membrane-stabilizing activity, salmeterol (25 and 50 microM) neutralized the haemolytic action of LPC, PAF and LPAF. 6. Of the other commonly used beta 2-adrenoceptor agonists, fenoterol, and formoterol, but not salbutamol, caused moderate inhibition of neutrophil oxidant generation by a superoxide-scavenging mechanism. However, unlike salmeterol, these agents possessed only weak membrane stabilizing properties. 7. We conclude that salmeterol antagonizes the pro-inflammatory, pro-oxidative activity of several bioactive lipids implicated in the pathogenesis of bronchial asthma, by a mechanism related to the membrane-stabilizing, rather than to the beta 2-agonist properties of this agent.

Synergistic effects among oxidants, membrane-damaging agents, fatty acids, proteinases, and xenobiotics: killing of epithelial cells and release of arachidonic acid

The assumption that cellular injury induced in infectious and in inflammatory sites might be the result of a well-orchestrated, synergistic "cross-talk" among oxidants, membrane-damaging agents, proteinases, and xenobiotics was further investigated in a tissue culture model employing monkey kidney epithelial cells (BGM) labeled either with 51 chromium or [3H]arachidonate. The cells could be killed in a synergistic manner following exposure to combinations among H2O2 and the following membrane-damaging agents: streptolysins S (SLS) and O (SLO), poly-D-lysine, arachidonic acid, eicosapentanoic acid, arachidic acid, lysophosphatidylcholine, lysophosphatidylinositol, lysophosphatidylglycerol, ethanol, and sodium taurocholate. Peroxyl radical (ROO) generated by azobisdiamidinopropane dihydrochloride (AAPH) further enhanced cell killing induced by SLS, SLO, and nitroprusside when combined with H2O2 and trypsin. BGM cells labeled either with chromium or with tritiated arachidonate, which had been treated with increasing concentrations of sodium nitroprusside (a donor of NO) and with subtoxic amounts of SLS and H2O2, were also killed in a synergistic manner and also lost a substantial amounts of their arachidonate label. Both cell killing and the release of membrane lipids were totally inhibited by hemoglobin (an NO scavenger) but not by methylene blue, an antagonist of NO2-BGM cells that had been treated with increasing concentrations of taurocholic acid were killed in a synergistic manner by a mixture of subtoxic amounts of ethanol, H2O2, and crystalline trypsin (quadruple synergism). Normal human serum possessing IgM complement-dependent cytotoxic antibodies against Ehrlich ascites tumor cells were killed in a dose-dependent fashion. Cell killing was doubled by the addition of H2O2. Cell killing and the release of membrane lipids by all the mixture of agonists tested were both strongly inhibited by the antioxidants catalase, Mn2+, vitamin A, and by fresh carrot juice. It appears that in order to overcome the antioxidant capacities of the epithelial cells, a variety of membrane-damaging agents had to be present in the reaction mixtures. Taken together, it might be speculated that the killing of mammalian cells in infectious and in inflammatory sites is a synergistic phenomenon that might be inhibited by antagonizing the cross-talk among the various proinflammatory agonists generated by microorganisms by activated phagocytes or by combinations among these agents. Our studies might also open up new approaches to the assessment of the toxicity of xenobiotics and of safe drugs to mammalian cells by employing tissue culture techniques.

The substrate specificities of four different lysophospholipases as determined by a novel fluorescence assay

A novel fluorescence assay for quantifying lysophospholipase activity is described which utilizes a commercially available acrylodated intestinal fatty-acid-binding protein (ADIFAB) and non-radiolabelled substrate. Quantification of enzyme activity is based on the decrease in ADIFAB fluorescence at 432 nm in the presence of nanomolar concentrations of non-esterified ('free') fatty acids. Lysophospholipase activity measured by the ADIFAB assay and a conventional radiometric assay yield comparable results and have comparable levels of sensitivity (approximately 10 pmol/min per ml). The ADIFAB assay has the advantageous features of continuous monitoring of enzyme activity and the availability of a broad range of potential substrates, because non-radiolabelled lysophospholipids can be employed in the assay. The hydrolytic activities of four lysophospholipases were determined, including a bacterial secreted phospholipase A2/lysophospholipase, the human-eosinophil-secreted lysophospholipase, a human intracellular lysophospholipase (peak 3) isolated from HL-60 cells and a high-molecular-mass cytosolic phospholipase A2/lysophospholipase from a mouse mammary carcinoma. Each of these enzymes was found to have a distinctive hydrolytic profile as determined by an array of lysophospholipids differing in their polar headgroups and sn-1 fatty-acyl substituents.

Retinoid toxicity for fibroblasts and epithelial cells is separable from growth promoting activity

Three different retinoids with widely varying capacity to stimulate skin repair in vivo and stimulate fibroblast and epithelial cell growth in vitro were examined for capacity to lyse the same cells at high concentrations. These included all-trans retinoic acid (RA), tetrahydro tetramethyl napthalenyl benzoic acid (TTNPB), and its biologically inactive structural analogue, meta-carboxy TTNPB. Despite their differing capacities to stimulate skin repair and cell growth, all of the agents were cytotoxic for fibroblasts and epithelial cells over the same range of concentrations (0.6-3 x 10(-5) M). Cytotoxicity for both fibroblasts and epithelial cells was blocked by addition of phosphatidylcholine to the cells along with the retinoid. In the presence of high concentrations of RA (0.75-3 x 10(-5) M) and phosphatidylcholine, proliferation was observed. The proliferative response was greater under these conditions than in the presence of an optimal concentration of RA (0.75-3 x 10(-6) M) without phosphatidylcholine. These data suggest that toxicity of retinoids can be separated, at least partially, from their growth-promoting activities.

Killing of endothelial cells and release of arachidonic acid. Synergistic effects among hydrogen peroxide, membrane-damaging agents, cationic substances, and proteinases and their modulation by inhibitors

51Chromium-labeled rat pulmonary artery endothelial cells (EC) cultivated in MEM medium were killed, in a synergistic manner, by mixtures of subtoxic amounts of glucose oxidase-generated H2O2 and subtoxic amounts of the following agents: the cationic substances, nuclear histone, defensins, lysozyme, poly-L-arginine, spermine, pancreatic ribonuclease, polymyxin B, chlorhexidine, cetyltrimethyl ammonium bromide, as well as by the membrane-damaging agents phospholipases A2 (PLA2) and C (PLC), lysolecithin (LL), and by streptolysin S (SLS) of group A streptococci. Cytotoxicity induced by such mixtures was further enhanced by subtoxic amounts either of trypsin or of elastase. Glucose-oxidase cationized by complexing to poly-L-histidine proved an excellent deliverer of membrane-directed H2O2 capable of enhancing EC killing by other agonists. EC treated with rabbit anti-streptococcal IgG were also killed, in a synergistic manner, by H2O2, suggesting the presence in the IgG preparation of cross-reactive antibodies. Killing of EC by the various mixtures of agonists was strongly inhibited by scavengers of hydrogen peroxide (catalase, dimethylthiourea, MnCl2), by soybean trypsin inhibitor, by polyanions, as well as by putative inhibitors of phospholipases. Strong inhibition of cell killing was also observed with tannic acid and by extracts of tea, but less so by serum. On the other hand, neither deferoxamine, HClO, TNF, nor GTP gamma S had any modulating effects on the synergistic cell killing. EC exposed either to 6-deoxyglucose, puromycin, or triflupromazin became highly susceptible to killing by mixtures of hydrogen peroxide with several of the membrane-damaging agents. While maximal synergistic EC killing was achieved by mixtures of H2O2 with either PLA2, PLC, LL, or with SLS, a very substantial release of [3H]arachidonic acid (AA), PGE2, and 6-keto-PGF occurred only if a proteinase was also added to the mixture of agonists. The release of AA from EC was markedly inhibited either by scavengers of H2O2, by proteinase inhibitors, by cationic agents, by HClO, by tannic acid, and by quinacrin. We suggest that cellular injury induced in inflammatory and infectious sites might be the result of synergistic effects among leukocyte-derived oxidants, lysosomal hydrolases, cytotoxic cationic polypeptides, proteinases, and microbial toxins, which might be present in exudates. These "cocktails" not only kill cells, but also solubilize AA and several of its metabolites. However, AA release by the various agonists can be also achieved following attack by leukocyte-derived agonists on dead cells. It is proposed that treatment by "cocktails" of adequate antagonists might be beneficial to protect against cellular injury in vivo.

Modulation of matrix vesicle enzyme activity and phosphatidylserine content by ceramic implant materials during endosteal bone healing

This study examined effects of bone bonding and nonbonding implants on parameters associated with matrix vesicle-mediated primary bone formation, matrix vesicle alkaline phosphatase and phospholipase A2 specific activities, and phosphatidylserine content. Tibia marrow ablation followed by implantation of KG-Cera, Mina 13 (bonding), KGy-213, or M 8/1 (nonbonding) was used as the experimental model. Postsurgery, matrix vesicle-enriched microsomes (MVEM) were isolated from implanted and contralateral limbs. MVEM alkaline phosphatase and phospholipase A2 were stimulated adjacent to bonding implants with similar, though reduced, effects contralaterally. Alkaline phosphatase exhibited slight stimulation in nonbonding tissue; phospholipase A2 was inhibited or unchanged in treated and contralateral limbs. Phosphatidylserine content of MVEM was differentially affected by the implant materials. Thus, MVEM are modulated by implant materials locally and systemically. The data demonstrate that the model is a biologically relevant diagnostic for assessing the tissue/implant interface, primary calcification is affected by implant materials, and implant-specific effects are detected in the contralateral unimplanted limb.

Oxygen radical scavengers selectively inhibit interleukin 8 production in human whole blood

The hydroxyl radical (OH.) scavenger dimethyl sulfoxide (DMSO) was found to dose-dependently inhibit interleukin 8 (IL-8) production in LPS-stimulated human whole blood. At a concentration of 1% (vol/vol), DMSO blocked IL-8 release by approximately 90% in the presence of 1 microgram/ml LPS at a 24-h time point, but did not affect cell viability or reduce the production of tumor necrosis factor (TNF), interleukin 6, or interleukin-1 beta (IL-1 beta). DMSO was found to directly inhibit IL-8 expression at the level of transcription. Furthermore, this effect was not LPS-specific, in that IL-8 production was reduced by DMSO to a similar extent upon stimulation of blood with phytohemagglutinin, aggregated immune complexes, TNF, or IL-1 beta. Other oxygen radical scavengers that have been shown to inhibit OH.-dependent reactions (dimethyl thiourea, thiourea, mannitol, and ethanol) also inhibited IL-8 production. Conversely, addition of H2O2 caused a dose-dependent stimulation of IL-8 release. These results provide evidence that reactive oxygen metabolites play an important role in the regulation of IL-8 production and suggest that reduction of IL-8 release may contribute to the beneficial effects of antioxidants in experimental models of inflammation and ischemia/reperfusion injury.

Synergism among oxidants, proteinases, phospholipases, microbial hemolysins, cationic proteins, and cytokines

A striking similarity exists between the pathogenetic properties of group A streptococci and those of activated mammalian professional phagocytes (neutrophils, macrophages). Both types of cells are endowed by the ability to adhere to target cells; to elaborate oxidants, hydrolases, and membrane-active agents (hemolysins, phospholipases); and to freely invade tissues and destroy cells. From the evolutionary point of view, streptococci might justifiably be considered the forefathers of "modern" leukocytes. Our earlier findings that synergy between a streptococcal hemolysin (streptolysin S, SLS) and a streptococcal thiol-dependent proteinase and between cytotoxic antibodies+complement and streptokinase-activated plasmin readily killed tumor cells, led us to hypothesize that by analogy to the pathogenetic mechanisms of streptococci, the mechanisms of tissue destruction initiated by activated leukocytes in inflammatory sites, as well as in tissues undergoing episodes of ischemia and reperfusion, might also be the result of the synergistic effects among leukocyte-derived oxidants, phospholipases, proteinases, cytokines, and cationic proteins. The current report extends our previous synergy studies with endothelial cells to two additional cell types--monkey kidney epithelial cells and rat beating heart cells. Monolayers of 51Cr-labeled cells that had been treated by combinations of sublytic amounts of hydrogen peroxide (generated either by glucose oxidase, xanthine-xanthine oxidase, or by paraquat) and with sublytic amounts of a variety of membrane-active agents (streptolysin S, phospholipases A2 and C, lysophosphatides, histone, chlorhexidine) were killed in a synergistic manner (double synergy). Crystalline trypsin markedly enhanced cell killing by combinations of oxidant and the membrane-active agents (triple synergy). Injury to the cells was characterized by the appearance of large membrane blebs that detached from the cells and floated freely in the media, looking like lipid droplets. Cytotoxicity induced by the various combinations of agonists was depressed, to a large extent, by scavengers of hydrogen peroxide (catalase, dimethyl thiourea, and by Mn2+) but not by SOD or by deferoxamine. When cationic agents were employed together with hydrogen peroxide, polyanions (heparin, polyanethole sulfonate) were also found to inhibit cell killing. It is proposed that in order to effectively combat the deleterious toxic effects of leukocyte-derived agonists on cells and tissues, antagonistic "cocktails" comprised of cationized catalase, cationized SOD, dimethylthiourea, Mn(2+)+glycine, proteinase inhibitors, putative inhibitors of phospholipases, and polyanions might be concocted. The current literature on synergistic phenomena pertaining to mechanisms of cell and tissue injury in inflammation is selectively reviewed.

Induction of proliferation of growth-inhibited keratinocytes and fibroblasts in monolayer culture by sodium lauryl sulfate: comparison with all-trans retinoic acid

We have previously shown that all-trans retinoic acid (RA) has the capacity to stimulate proliferation of growth-inhibited human epidermal keratinocytes and growth-inhibited human dermal fibroblasts. The same treatment also stimulates extracellular matrix synthesis by fibroblasts (J Invest Dermatol 93:449; 94:717). In the present study we have examined the capacity of sodium lauryl sulfate to stimulate keratinocyte and fibroblast proliferation under the same conditions. Our data show that both cell types are stimulated to proliferate. Sodium lauryl sulfate is less potent than RA; it requires a higher molar concentration to achieve optimal stimulation and the number of responding cells at optimal concentrations is less with sodium lauryl sulfate than with RA. Further, there is a rapid onset of toxicity at concentrations of sodium lauryl sulfate that are only slightly higher than the optimal stimulatory concentration. Finally, sodium lauryl sulfate is less effective than RA in stimulating production of extracellular matrix (fibronectin, thrombospondin, and laminin) by dermal fibroblasts. Despite its ability to partially mimic RA as a stimulant of keratinocyte and fibroblast growth, sodium lauryl sulfate does not activate chloramphenicol acetyl transferase in cells co-transfected with retinoic acid receptors and a retinoic acid responsive element linked to the chloramphenicol acetyl transferase gene.

Thin-layer and liquid column chromatographic analyses of the lipids of adult Onchocerca gibsoni

Lipids were extracted from adult Onchocerca gibsoni with chloroform/methanol and the total lipid content was characterized. Glycolipids were isolated from other lipid classes by Florisil column chromatography and were then fractionated by DEAE-Sephadex ion-exchange chromatography. HPTLC revealed the presence of 9 neutral glycolipid bands and of 15 acidic glycolipid bands that stained for sialic acid with resorcinol. Lipids that contained no carbohydrates were analyzed by a combination of TLC and amino column chromatography. Triacylglycerols, cholesterol, cholesterol esters, and free fatty acids were found to be major components of the neutral lipid fraction, and diacylglycerols and monoacylglycerols were minor components. Phosphatidylethanolamine and phosphatidylcholine were the predominant phospholipids. Phosphatidylserine, phosphatidylinositol, sphingomyelin, lysophosphatidylcholine, and lysophosphatidylethanolamine were also present in significant amounts, whereas only traces of cardiolipin and phosphatidic acid were detected. Several minor lipids and phospholipids remained unidentified. These results indicate that adult O. gibsoni have a nonglycosylated lipid composition resembling that of other parasitic nematodes as well as a substantial repertoire of glycolipids, including many with the characteristics of gangliosides.

Cationic polyelectrolytes: potent opsonic agents which activate the respiratory burst in leukocytes

Bacteria and yeasts which are "opsonized" with cationic polyelectrolytes (poly-L-arginine, poly-L-histidine and arginine-rich histone) are avidly endocytosed by both "professional" and "non-professional" phagocytes. The cationized particles also strongly activate the respiratory burst in neutrophils and in macrophages leading to the generation of chemiluminescence, superoxide and hydrogen peroxide. On the other hand, lysine and ornithine-rich polymers are poor opsonic agents. Poly L-arginine is unique in its capacity to act synergistically with lectins, with chemotactic peptides and with cytochalasin B to generate large amounts of chemiluminescence and superoxide in human neutrophils. Unlike polyarginine, polyhistidine, in the absence of carrier particles, is one of the most potent stimulators of superoxide generations, known. Neutrophils treated with cetyltrimethylammonium bromide fail to generate superoxide, but generate strong luminol-dependent chemiluminescence which is totally inhibited by sodium azide and by thiourea. Neutrophils injured by cytolytic agents (saponin, digitonin, lysolecithin) lose their chemiluminescence and superoxide-generating capacities upon stimulation by a variety of ligands. These activities are however regained by the addition of NADPH. Lysolecithin can replace polyarginine in a "cocktail" also containing lectins and cytochalasin B, which strongly activate the respiratory burst. This suggests that polyarginine acts both as a cytolytic agent and as a ligand. Arginine and histidine-rich polyelectrolytes enhance the pathogenic effects of immune complexes in vivo (reversed Arthus phenomenon) presumably by "glueing" them to tissues. Polyhistidine complexed to catalase or to superoxide dismutase, markedly enhances their efficiency as antioxidants. On the other hand polyhistidine complexed to glucose oxidase markedly enhances injury to endothelial cells suggesting that the close association of the cationized enzyme with the plasma membrane facilitates the interaction of hydrogen peroxide with the targets. A variety of cationic agents (histone, polyarginine, polyhistidine, polymyxin B) and membrane-active agents (lysophosphatides, microbial hemolysins) act synergistically with glucose oxidase or with reagent hydrogen peroxide to kill target cells. The mechanisms by which arginine- and histidine-rich polyelectrolytes activate the respiratory burst in neutrophils might involve interaction with G-proteins, the activation of arachidonic acid metabolism and phospholipase A2, or the interaction with myeloperoxidase. Naturally-occurring cationic proteins might modulate several important functions of leukocytes and the course and outcome of the inflammatory process.

Vascular endothelial cell killing by combinations of membrane-active agents and hydrogen peroxide

Previous studies have demonstrated that a number of membrane-active agents are capable of binding to the surface of polymorphonuclear leukocytes (PMN) resulting in an augmentation of superoxide anion and hydrogen peroxide (H2O2) production in response to soluble stimuli. It is now demonstrated that these same membrane-active agents can bind to the surface of endothelial cells and enhance their susceptibility to killing by H2O2. Membrane-active agents which are capable of synergizing with H2O2 include cationic proteins, cationic poly-amino acids, lysophosphatides and enzymes which are capable of degrading membrane phospholipids (e.g., phospholipase C, phospholipase A2 and streptolysin S). In each case, treatment of the target cells with the membrane-active agent and H2O2 produces greater damage than the sum of the damage produced by either agent separately. Since inflammatory lesions, particularly sites of bacterial infection, may contain a rich mixture of cationic substances, phospholipases and phospholipid breakdown products, these substances may contribute to the tissue damage observed at sites of inflammation by enhancing endothelial cell sensitivity to PMN-generated H2O2 as well as by augmenting the generation of H2O2 by PMNs.