Cleavage of the fifth component of human complement and release of a split product with C5a-like activity by crystalline silica through free radical generation and kallikrein activation

Biomaterial and cellular implants:foreign surfaces where immunity and coagulation meet

Exposure of blood to a foreign surface in the form of a diagnostic or therapeutic biomaterial device or implanted cells or tissues, elicits an immediate, evolutionarily conserved thrombo-inflammatory response by the host. Primarily designed to protect against invading organisms following an injury, this innate response features instantaneous activation of several blood-borne, highly interactive and well-orchestrated cascades and cellular events that limit bleeding, destroy and eliminate the foreign substance/cells, and promote healing and a return to homeostasis via delicately balanced regenerative processes. In the setting of blood-contacting synthetic or natural biomaterials and implantation of foreign cells/tissues, innate responses are robust, albeit highly context-specific. Unfortunately, they tend to be less than adequately regulated by the host's natural anti-coagulant/anti-inflammatory pathways, thereby jeopardizing the functional integrity of the device, as well as the health of the host. Strategies to achieve biocompatibility with a sustained return to homeostasis, particularly while the device remains in situ and functional, continue to elude scientists and clinicians. In this review, some of the complex mechanisms by which biomaterials and cellular transplants provide a "hub" for activation and amplification of coagulation and immunity - thrombo-inflammation - will be discussed, with a view toward the development of innovative means of overcoming the innate challenges.

Plasma Kallikrein-Kinin system mediates immune-mediated renal injury in trichloroethylene-sensitized mice

Trichloroethylene (TCE) is a major environmental pollutant. An immunological response is a newly-recognized mechanism for TCE-induced kidney damage. However, the role of the plasma kallikrein-kinin system (KKS) in immune-mediated kidney injury has never been examined. This study aimed to explore the role of the key components of the KKS, i.e. plasma kallikrein (PK), bradykinin (BK) and its receptors B1R and B2R, in TCE-induced kidney injury. A mouse model of skin sensitization was used to explore the mechanism of injury with or without a PK inhibitor PKSI. Kidney function was evaluated by measuring blood urea nitrogen (BUN) and creatinine (Cr) in conjunction with histopathologic characterization. Plasma BK was determined by ELISA; Renal C5b-9 membrane attack complex was evaluated by immunohistochemistry. Expression of BK and PK in the kidney was detected by immunofluorescence. mRNA and protein levels of B1R and B2R were assessed by real-time qPCR and Western blot. As expected, numerous inflammatory cell infiltration and tubular epithelial cell vacuolar degeneration were observed in TCE-sensitized mice. Moreover, serum BUN and Cr and plasma BK were increased. In addition, deposition of BK, PK and C5b-9 were observed and B1R and B2R mRNA and proteins levels were up-regulated. Pre-treatment with PKSI, a highly selective inhibitor of PK, alleviated TCE-induced renal damage. In addition, PKSI attenuated TCE-induced up-regulation of BK, PK and its receptors and C5b-9. These results provided the first evidence that activation of the KKS contributed to immune-mediated renal injury induced by TCE and also helped to identify the KKS as a potential therapeutic target for mitigating chemical sensitization-induced renal damage.

Evasion and interactions of the humoral innate immune response in pathogen invasion, autoimmune disease, and cancer

The humoral innate immune system is composed of three major branches, complement, coagulation, and natural antibodies. To persist in the host, pathogens, such as bacteria, viruses, and cancers must evade parts of the innate humoral immune system. Disruptions in the humoral innate immune system also play a role in the development of autoimmune diseases. This review will examine how Gram positive bacteria, viruses, cancer, and the autoimmune conditions systemic lupus erythematosus and anti-phospholipid syndrome, interact with these immune system components. Through examining evasion techniques it becomes clear that an interplay between these three systems exists. By exploring the interplay and the evasion/disruption of the humoral innate immune system, we can develop a better understanding of pathogenic infections, cancer, and autoimmune disease development.

Raw and thermally treated cement asbestos exerts different cytotoxicity effects on A549 cells in vitro

Raw cement asbestos (RCA) undergoes a complete solid state transformation when heated at high temperatures. The secondary raw material produced, high temperatures-cement asbestos (HT-CA) is composed of newly-formed crystals in place of the asbestos fibers present in RCA. Our previous study showed that HT-CA exerts lower cytotoxic cell damage compared to RCA. Nevertheless further investigations are needed to deepen our understanding of pathogenic pathways involving oxidative and nitrative damage. Our aim is to deepen the understanding of the biological effects on A549 cells of these materials regarding DNA damage related proteins (p53, its isoform p73 and TRAIL) and nitric oxide (NO) production during inducible nitric oxide synthase (iNOS)-mediated inflammation. Increments of p53/p73 expression, iNOS positive cells and NO concentrations were found with RCA, compared to HT-CA and controls mainly at 48 h. Interestingly, ferrous iron causing reactive oxygen species (ROS)-mediated DNA damage was found in RCA as a contaminant. HT-CA thermal treatment induces a global recrystallization with iron in a crystal form poorly released in media. HT-CA slightly interferes with genome expression and exerts lower inflammatory potential compared to RCA on biological systems. It could represent a safe approach for storing or recycling asbestos and an environmentally friendly alternative to asbestos waste.

Indications for distinct pathogenic mechanisms of asbestos and silica through gene expression profiling of the response of lung epithelial cells

Occupational and environmental exposures to airborne asbestos and silica are associated with the development of lung fibrosis in the forms of asbestosis and silicosis, respectively. However, both diseases display distinct pathologic presentations, likely associated with differences in gene expression induced by different mineral structures, composition and bio-persistent properties. We hypothesized that effects of mineral exposure in the airway epithelium may dictate deviating molecular events that may explain the different pathologies of asbestosis versus silicosis. Using robust gene expression-profiling in conjunction with in-depth pathway analysis, we assessed early (24 h) alterations in gene expression associated with crocidolite asbestos or cristobalite silica exposures in primary human bronchial epithelial cells (NHBEs). Observations were confirmed in an immortalized line (BEAS-2B) by QRT-PCR and protein assays. Utilization of overall gene expression, unsupervised hierarchical cluster analysis and integrated pathway analysis revealed gene alterations that were common to both minerals or unique to either mineral. Our findings reveal that both minerals had potent effects on genes governing cell adhesion/migration, inflammation, and cellular stress, key features of fibrosis. Asbestos exposure was most specifically associated with aberrant cell proliferation and carcinogenesis, whereas silica exposure was highly associated with additional inflammatory responses, as well as pattern recognition, and fibrogenesis. These findings illustrate the use of gene-profiling as a means to determine early molecular events that may dictate pathological processes induced by exogenous cellular insults. In addition, it is a useful approach for predicting the pathogenicity of potentially harmful materials.

The role of complement in tumor growth

Complement is a central part of the immune system that has developed as a first defense against non-self cells. Neoplastic transformation is accompanied by an increased capacity of the malignant cells to activate complement. In fact, clinical data demonstrate complement activation in cancer patients. On the basis of the use of protective mechanisms by malignant cells, complement activation has traditionally been considered part of the body's immunosurveillance against cancer. Inhibitory mechanisms of complement activation allow cancer cells to escape from complement-mediated elimination and hamper the clinical efficacy of monoclonal antibody-based cancer immunotherapies. To overcome this limitation, many strategies have been developed with the goal of improving complement-mediated effector mechanisms. However, significant work in recent years has identified new and surprising roles for complement activation within the tumor microenvironment. Recent reports suggest that complement elements can promote tumor growth in the context of chronic inflammation. This chapter reviews the data describing the role of complement activation in cancer immunity, which offers insights that may aid the development of more effective therapeutic approaches to control cancer.

International Union of Basic and Clinical Pharmacology. [corrected]. LXXXVII. Complement peptide C5a, C4a, and C3a receptors

The activation of the complement cascade, a cornerstone of the innate immune response, produces a number of small (74-77 amino acid) fragments, originally termed anaphylatoxins, that are potent chemoattractants and secretagogues that act on a wide variety of cell types. These fragments, C5a, C4a, and C3a, participate at all levels of the immune response and are also involved in other processes such as neural development and organ regeneration. Their primary function, however, is in inflammation, so they are important targets for the development of antiinflammatory therapies. Only three receptors for complement peptides have been found, but there are no satisfactory antagonists as yet, despite intensive investigation. In humans, there is a single receptor for C3a (C3a receptor), no known receptor for C4a, and two receptors for C5a (C5a₁ receptor and C5a₂ receptor). The most recently characterized receptor, the C5a₂ receptor (previously known as C5L2 or GPR77), has been regarded as a passive binding protein, but signaling activities are now ascribed to it, so we propose that it be formally identified as a receptor and be given a name to reflect this. Here, we describe the complex biology of the complement peptides, introduce a new suggested nomenclature, and review our current knowledge of receptor pharmacology.

Recent developments in low molecular weight complement inhibitors

As a key part of the innate immune system, complement plays an important role not only in defending against invading pathogens but also in many other biological processes. Inappropriate or excessive activation of complement has been linked to many autoimmune, inflammatory, and neurodegenerative diseases, as well as ischemia-reperfusion injury and cancer. A wide array of low molecular weight complement inhibitors has been developed to target various components of the complement cascade. Their efficacy has been demonstrated in numerous in vitro and in vivo experiments. Though none of these inhibitors has reached the market so far, some of them have entered clinical trials and displayed promising results. This review provides a brief overview of the currently developed low molecular weight complement inhibitors, including short peptides and synthetic small molecules, with an emphasis on those targeting components C1 and C3, and the anaphylatoxin receptors.

Kinetics of radical formation during the mechanical activation of quartz

The kinetics of radical formation during the mechanical activation of quartz by wet grinding or sonication was investigated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) as a scavenger. The consumption of DPPH during the sonication of quartz in an ethanol suspension is a zeroth-order process. A linear relationship between the rate constant of the DPPH consumption and the quartz concentration in the suspension indicates that radical formation under sonication increases with the growing total surface area of the quartz particles. Sonication leads to the formation of free radicals by the mechanical activation of the particle surface. The kinetics of the DPPH consumption during wet grinding of quartz in a stirred media mill is described successfully by a modified zeroth-order rate law taking the total surface area of the quartz particles into account. The surface-normalized rate constant of the DPPH consumption decreases from 1.8x10(-7) mol L(-1) h(-1) m(-2) to 4.8x10(-8) mol L(-1) h(-1) m(-2) if the specific surface area of the feed material increases from 0.5 to 84 m2/g. This finding indicates that the breakage of the quartz particles contributes much more to radical formation than does the mechanical activation of the particles in the mill because the breakage rate increases with growing particle diameter. Ethanol but not DPPH was found on the surface of the ground quartz particles. From this finding, it can be concluded that radicals on the surface of the quartz particles react with ethanol, leading to the formation of ethanol radicals and H radicals. DPPH reacts with the H radicals. As a side reaction, radicals can react with oxygen, leading to the formation of peroxides.

Aprotinin in Cardiac Surgery: A Review of Conventional and Novel Mechanisms of Action

Induction of the coagulation and inflammatory cascades can cause multiorgan dysfunction after cardiopulmonary bypass (CPB). In light of these observations, strategies that can stabilize the coagulation process as well as attenuate the inflammatory response during and after cardiac surgery are important. Aprotinin has effects on hemostasis. In addition, aprotinin may exert multiple biologically relevant effects in the context of cardiac surgery and CPB. For example, it decreases neutrophil and macrophage activation and chemotaxis, attenuates release and activation of proinflammatory cytokines, and reduces oxidative stress. Despite these perceived benefits, the routine use of aprotinin in cardiac surgery with CPB has been called into question. In this review, we examined this controversial drug by discussing the classical and novel pathways in which aprotinin may be operative in the context of cardiac surgery.

Variability of biological effects of silicas: Different degrees of activation of the fifth component of complement by amorphous silicas

A biogenic and a pyrogenic amorphous silica were incubated in normal human plasma and compared on a per unit surface basis for their ability to split C5 molecules and yield small C5a peptides. Since C5a peptides induce selective chemotactic attraction of polymorphonuclear leukocytes (PMN), measurement of PMN-induced chemotaxis was used as an index of C5 activation. Though to a lesser extent than the crystalline forms, amorphous silicas can promote the cleavage of C5 protein and generation of C5a-like fragment. The biogenic silica, which differs from the pyrogenic variety in particle shape, level of contaminants, and degree of surface hydrophilicity, besides specific surface, induced a greater response. Both silicas activated C5 through a process which seems to involve multiple events similar to those induced by crystalline silica. C5 molecules are adsorbed and hydroxyl radicals are generated through Haber Weiss cycles catalyzed by the redox-active iron present at the particle surface either as trace impurities or chelated from plasma by silanol groups. In turn, these radicals convert native C5 to an oxidized C5-like form C5(H2O2). Finally, C5(H2O2) is cleaved by protease enzymatic action of plasma kallikrein activated by the same silica dusts, yielding a product, C5a(H2O2), having the same functional characteristic as C5a.

Serum exposed to nanoparticle carbon black displays increased potential to induce macrophage migration

OBJECTIVE

To assess whether fine and ultrafine particles (nanoparticles) have the capacity to activate factors in serum that would induce macrophage migration. This is a model previously reported to investigate complement activation by other respirable particles and fibres.

METHOD

Foetal bovine serum was exposed to varying doses of fine and nanoparticle carbon black as well as the oxidant tert-butyl hydroperoxide (tBHP). The subsequent potential of the serum to induce macrophage migration was measured using a macrophage chemotaxis assay.

RESULTS

Treatment of serum with 10 mg/ml of nanoparticle carbon black generated substances that induced a 1.8-fold increase in macrophage migration (P<0.001) compared with untreated serum. This effect was partially inhibited by antioxidant intervention. Serum treated with an equivalent mass of fine carbon black did not display any chemotactic potential. tBHP treatment of the serum did not result in the generation of macrophage chemotactic factors.

CONCLUSIONS

High doses of nanoparticle carbon black have the capacity to cause chemotactic factor generation in serum, by a mechanism involving ROS generation, although ROS alone, in the form of tBHP are not adequate to generate chemotactic factors in serum.

Relationship between the state of the surface of four commercial quartz flours and their biological activity in vitro and in vivo

Four commercial quartz dusts (flours), two inflammogenic in vivo and activating macrophages in vitro (Qz 2/1-c and Qz 3/1-c) and two mostly inert (Qz 5/1-c and Qz 11/1-c), have been compared regarding their surface properties, in order to detect chemical differences which may account for their different biological behaviour. The following features have been examined: 1) extent of the amorphous fraction (heat associated alpha<-->beta transition of quartz) and its solubility in HF; 2) potential to cleave a carbon-hydrogen bond with consequent generation of carbon centred radicals (spin trapping technique, EPR); 3) evolution of surface functionalities upon heating (FTIR spectroscopy); 4) mechanisms of adsorption of water on dusts outgassed at 150 degrees and at 800 degrees C (adsorption calorimetry). HCl treated samples have also been examined. The two "less toxic" quartzes are more resistant to HF attack, coordinate irreversibly H2O molecules and exhibit strong adsorption sites, which are absent in the other two and in a very pure quartz dust. Conversely all samples show the same potential to release free radicals. The different behaviour of the two sets of dust is consistent with a different level of impurities, namely aluminium ex kaolin, carbon and alkaline ions. The less inflammogenic quartzes appear to be covered by aluminium ions (and possibly iron) which strongly holds molecular water or carbonates, thus reducing the silanol patches to a large extent and changing the surface properties of the particles. We hypothesize that cellular response, and particularly macrophage activation and death, is mediated by strong interactions between silanol patches and some cell membrane components, but inhibited when the surface of the particle is modified by the presence of aluminium ions, surface carbonates and other metal contaminants. This hypothesis suggests that grinding procedures with little appropriate additives, e.g. kaolin, alumina, can reduce the biological activity of quartz dusts.

Role of substrate on larval development of the freshwater teleostPelvicachromis pulcher

It is known that, in an aquatic environment, the mineralogical composition of the substrate can affect the structure of settled communities. In marine environments, the presence of quartz negatively influences the formation of biofilm, as well as the selection and the colonization of the substrate by benthic organisms. Direct laboratory observation revealed that the freshwater teleost Pelivicachromis pulcher selects, when available, nonquartzitic brooding substrate. To monitor the effects of substrate on larvae development, ten lots of embryos were distributed in grid nurseries; carbonatic gravel was laid in five of the nurseries, while freshly fractured quartz gravel was used in the remaining ones. All the embryos laid in the two nurseries hatched, and 90% of the carbonate developing larvae reached adulthood, while 100% of those reared on quartz grain died 120 hr post hatching. Examination was made, both in larvae developed on carbonatic substrates and in those developed on quartz substrates, of the expression of the fetal growth factor, the insulin growth factor-II (IGF-II), of the molecular chaperone, the heat shock protein 70 (HSP70), which is involved in the folding of the nascent polypeptide chain, of the key enzyme of the glycolytic pathway, the glyceraldehyde-3-phosphate dehydrogenase (GADPH), and of the housekeeping gene, the beta-actin. All the data were normalized against 18S RNA expression. In larvae reared on quartz substrate, the genes IGF-II and the beta-actin showed a lower expression, while the GADPH was totally suppressed and the expression of HSP70 increased. In conclusion, the data presented in this article demonstrated, for the first time, that the presence of quarzitic substrates is sufficient to stop larvae development through the inhibition of gene transcription in this African cichlid, leading to its death.