Complement activation on thiol-modified gold surfaces

Therapeutic regulation of complement activation in extracorporeal circuits and intravascular treatments with special reference to the alternative pathway amplification loop

A number of clinical treatment modalities involve contact between blood and biomaterials: these include extracorporeal circuits such as hemodialysis, cardiopulmonary bypass, plasmapheresis, and intravascular treatments. Common side effects arising from these treatments are caused by activation of the cascade systems of the blood. Many of these side effects are mediated via the complement system, including thromboinflammatory reactions and rejection of implants. Depending on the composition of the materials, complement activation is triggered via all the activation pathways but is by far mostly driven by the alternative pathway amplification loop. On biomaterial surfaces the alternative pathway amplification is totally unregulated and leads under optimal conditions to deposition of complement fragments, mostly C3b, on the surface leading to a total masking of the underlying surface. In this review, we discuss the mechanism of the complement activation, clinical consequences of the activation, and potential strategies for therapeutic regulation of the activation, using hemodialysis as demonstrator.

Control of innate immune response by biomaterial surface topography, energy, and stiffness

As the focus of implantable biomaterials has shifted from bioinert implants to bioactive designs, recent research has highlighted the complex interactions between cell physiologic systems and material properties, particularly physical cues. From the cells known to interact with implanted biomaterials, the response of the immune system has been a critical target of study recently. Here, we review studies characterizing the response of innate immune cells to various material cues, particularly of those at the surface of implanted materials.The innate immune system consists of cell types with various roles in inflammation. Neutrophils and macrophages serve both phagocytic and signaling roles, especially early in the inflammatory phase of biomaterial implantation. These cell types ultimately dictate the outcome of implants as chronic inflammation, fibrosis, or integration. Other cell types like dendritic cells, mast cells, natural killer cells, and innate lymphoid cells may also serve an immunomodulatory role in the biomaterial context. This review highlights recent advances in our understanding of the role of innate immunity in the response to implantable biomaterials as well as key mechanobiological findings in innate immune cells underpinning these advances. STATEMENT OF SIGNIFICANCE: This review highlights recent advances in the understanding of the role of innate immunity in the response to implantable biomaterials, especially in neutrophils and macrophages, as well as key mechanobiological findings in innate immune cells underpinning these advances. Here we discuss how physicochemical properties of biomaterials control innate immune cell behavior.

A new trick for an ancient drug: quinine dissociates antiphospholipid immune complexes

Quinine, a quinoline derivative, is an ancient antipyretic drug with antimalarial properties that has been phased out by more effective synthetic candidates. In previous studies we discovered that hydroxychloroquine (HCQ), a synthetic antimalarial with structural similarities to quinine, reduced the binding of antiphospholipid (aPL) immune complexes to phospholipid bilayers. We performed ellipsometry and atomic force microscopy (AFM) studies to measure the effect of quinine on dissociation of anti-β2-glycoprotein I (anti-β2GPI) immune complexes. We found that quinine desorbed pre-formed β2GPI-aPL immunoglobulin (Ig)G complexes from phospholipid bilayers at significantly lower molar concentrations than HCQ. Quinine also inhibited the formation of immune complexes with a higher efficacy than HCQ at equivalent drug concentrations of 0.2 mg/ml (0.192 ± 0.025 µg/cm(2) for quinine vs. 0.352 ± 0.014 µg/cm(2) for HCQ, p < 0.001). Furthermore, AFM imaging experiments revealed that addition of quinine disintegrated immune complexes bound to planar phospholipid layers. The desorptive and inhibitory effects of the old drug, quinine, toward β2GPI-aPL IgG complexes and β2GPI were significantly more pronounced compared to the synthetic antimalarial, HCQ. The results suggest that the quinoline core of the molecule is a critical domain for this activity and that side chains may further modulate this effect. The results also indicate that there may yet be room for considering new activities of very old drugs in devising clinical trials on potential non-anticoagulant treatments for antiphospholipid syndrome (APS).

Understanding and controlling the interaction of nanomaterials with proteins in a physiological environment

Nanomaterials hold promise as multifunctional diagnostic and therapeutic agents. However, the effective application of nanomaterials is hampered by limited understanding and control over their interactions with complex biological systems. When a nanomaterial enters a physiological environment, it rapidly adsorbs proteins forming what is known as the protein 'corona'. The protein corona alters the size and interfacial composition of a nanomaterial, giving it a biological identity that is distinct from its synthetic identity. The biological identity determines the physiological response including signalling, kinetics, transport, accumulation, and toxicity. The structure and composition of the protein corona depends on the synthetic identity of the nanomaterial (size, shape, and composition), the nature of the physiological environment (blood, interstitial fluid, cell cytoplasm, etc.), and the duration of exposure. In this critical review, we discuss the formation of the protein corona, its structure and composition, and its influence on the physiological response. We also present an 'adsorbome' of 125 plasma proteins that are known to associate with nanomaterials. We further describe how the protein corona is related to the synthetic identity of a nanomaterial, and highlight efforts to control protein-nanomaterial interactions. We conclude by discussing gaps in the understanding of protein-nanomaterial interactions along with strategies to fill them (167 references).

Surface plasmon resonance in monitoring of complement activation on biomaterials

When artificial materials come into contact with blood, various biological responses are induced. For successful development of biomaterials used in biomedical devices that will be exposed to blood, understanding and control of these interactions are essential. Surface plasmon resonance (SPR) spectroscopy is one of the surface-sensitive optical methods to monitor biological interactions. SPR enables real-time and in situ analysis of interfacial events associated with biomaterials research. In this review, we describe an SPR biosensor and its application to monitor complement activation onto biomaterials surface. We also discuss the effect of surface properties of the material on complement activation.

Surface chemistry influences implant biocompatibility

Implantable medical devices are increasingly important in the practice of modern medicine. Unfortunately, almost all medical devices suffer to a different extent from adverse reactions, including inflammation, fibrosis, thrombosis and infection. To improve the safety and function of many types of medical implants, a major need exists for development of materials that evoked desired tissue responses. Because implant-associated protein adsorption and conformational changes thereafter have been shown to promote immune reactions, rigorous research efforts have been emphasized on the engineering of surface property (physical and chemical characteristics) to reduce protein adsorption and cell interactions and subsequently improve implant biocompatibility. This brief review is aimed to summarize the past efforts and our recent knowledge about the influence of surface functionality on protein:cell:biomaterial interactions. It is our belief that detailed understandings of bioactivity of surface functionality provide an easy, economic, and specific approach for the future rational design of implantable medical devices with desired tissue reactivity and, hopefully, wound healing capability.

Increased optical contrast in imaging of epidermal growth factor receptor using magnetically actuated hybrid gold/iron oxide nanoparticles

We describe a new approach for optical imaging that combines the advantages of molecularly targeted plasmonic nanoparticles and magnetic actuation. This combination is achieved through hybrid nanoparticles with an iron oxide core surrounded by a gold layer. The nanoparticles are targeted in-vitro to epidermal growth factor receptor, a common cancer biomarker. The gold portion resonantly scatters visible light giving a strong optical signal and the superparamagnetic core provides a means to externally modulate the optical signal. The combination of bright plasmon resonance scattering and magnetic actuation produces a dramatic increase in contrast in optical imaging of cells labeled with hybrid gold/iron oxide nanoparticles.

Inflammatory responses and cell adhesion to self-assembled monolayers of alkanethiolates on gold

The acute inflammatory response and the adhesion of cells to self-assembled monolayers (SAMs) of well-defined surface chemistry was studied in vivo using a rodent air-pouch model of inflammation. SAMs with three different terminal functional groups (OH, COOH and CH3) were implanted in subcutaneous air pouches induced in BALB/c mice. After 24 h, inflammatory cells were recovered from the air pouches and the implants were removed and prepared for observation by scanning electron microscopy (SEM). The implants coated with OH and CH3, were found to cause the highest recruitment of inflammatory cells into the subcutaneous pouches. Polymorphonuclear neutrophils (PMNs) leukocytes predominated over mononuclear cells in inflammatory exudates of SAMs-coated implants, the opposite being found in uncoated implants (controls). CH3-coated implants induced the highest number of inflammatory cells and also the largest percentage of PMNs seen in the subcutaneous pouches. Control and OH-covered implants presented the higher densities of attached inflammatory cells detected by SEM. In contrast, the CH3-coated implants showed a very low density of cells adherent to the implant surface. We conclude that the chemical nature and the degree of hydrophobicity of the surface of implants modulate both the local acute inflammatory reaction and the adhesion of leukocytes.

On the binding of complement to solid artificial surfaces in vitro

Since the realization of a complement activation capacity by artificial surfaces upon contact with blood, a common belief has evolved that charged nucleophilic surface groups such as amine (-NH2) and hydroxyl (-OH) react with and eventually bind to the internal thioester in complement factor 3 (C3). A covalent amide or ester linkage is thereby supposed to form between C3b and the surface itself. In this report, we present complement surface binding data by null-ellipsometry for two nucleophilic surfaces (-NH2 and -OH), for surfaces with immunoglobulin G (IgG) covalently bound, and for IgG spontaneously pre-adsorbed to hydrophobic silicon. The results reveal that the plasma proteins that were deposited during complement activation became eluted by sodium dodecyl sulfate. Hence the direct covalent binding between C3 and solid nucleophilic surfaces seems to be only of moderate importance, at least during shorter serum incubations. This strongly suggests that the prevalent covalent linkage model between solid artificial surfaces and C3b is not accurate. Instead we suggest a more pronounced role for C3 associations to other adsorbed proteins and or electrostatic and hydrophobic protein-surface interactions.

Complement activation on immunoglobulin G-coated hydrophobic surfaces enhances the release of oxygen radicals from neutrophils through an actin-dependent mechanism

Neutrophil granulocytes are among the first cells to encounter a plasma protein-coated implant and may through frustrated phagocytosis release toxic oxidative species. We used two model surfaces, hydrophobic and hydrophilic glass, to investigate the effects of plasma immunoglobulin G (IgG)-complement interactions for neutrophil adhesion and respiratory burst. The respiratory burst was measured with luminol-amplified chemiluminescence and cell adhesion was determined by labeling neutrophils with 2', 7'-bis-(carboxy-ethyl)-5(6)-carboxyfluorescein. We demonstrate that the IgG-triggered neutrophil adhesion and oxygen radical production is augmented in the presence of normal human serum, in particular on hydrophobic surfaces, indicating that complement factors enhance the neutrophil activation. We propose that the complement factors C3, C5a, and C1q are especially important for this amplification, but factor B is probably not. Disturbance of the actin filament dynamics with cytochalasin B or jasplakinolide blocked the neutrophil radical generation on all surfaces. However, these drugs did not affect the number of adherent neutrophils. We suggest that there is a synergistic interaction between adsorbed IgG, and the complement system, which amplifies the neutrophil acute inflammatory responses through a dynamic actin cytoskeleton on synthetic surfaces.

Adsorbed IgG: a potent adhesive substrate for human macrophages

Previous reports from our laboratory have demonstrated qualitatively that preabsorbed IgG can enhance long-term macrophage adhesion in vitro. This investigation further characterizes and quantifies the biological effect of adsorbed human IgG on human macrophages and probes the potential mechanisms. Ten-day human monocyte/macrophage cultures on Plastek M (PM), a normally poor cellular substrate for macrophages, confirmed the ability of preabsorbed IgG to dramatically enhance long-term macrophage adhesion. An adsorption solution concentration of 200 microg/mL of IgG was necessary to provide a consistent, optimal cellular response. (125)I adsorption studies indicated Langmuir-style IgG adsorption at low concentrations; however, no adsorption maximum was observed. Additional adsorption analysis revealed that the IgG fragments Fab, F(ab')(2), and Fc adsorb at levels only 20-40% that of the whole molecule. Despite the lower adsorption levels, both preabsorbed Fab and F(ab')(2) were shown to be as effective as whole molecule IgG at enhancing long-term macrophage adhesion. Surprisingly, the preabsorbed Fc fragment demonstrated no IgG-like activity, thereby eliminating the possibility of an Fc receptor-based mechanism. Other possible mechanisms, such as macrophage lectins, novel macrophage Fab receptors, and complement activation by adsorbed IgG and IgG fragments, are discussed.

Peptide modified gold-coated polyurethanes as thrombin scavenging surfaces

Thin layers of gold were deposited on polyurethane film and chemisorbed with three peptides having an N-terminal cysteine: Cys-Pro-Arg, Cys-(L)Phe-Pro-Arg, and Cys-(D)Phe-Pro-Arg. The ability of these surfaces to act as thrombin scavengers was evaluated. The peptides are related to the known thrombin inhibitor Phe-Pro-Arg chloromethyl ketone and were shown to have significant thrombin inhibitory activity in solution. Attachment of the peptides to gold was confirmed by water contact angle and X-ray photoelectron spectroscopy measurements. Thrombin adsorption from a buffer and plasma was investigated, and chromogenic substrate assays were carried out for thrombin activity on the surfaces and in the supernatant following adsorption. The data suggest that the peptide-modified surfaces are able to adsorb thrombin with high affinity from a buffer and that thrombin is taken up selectively from plasma. The Cys-(D)Phe-Pro-Arg modified surfaces showed particularly high affinity for thrombin. It was also found that the activity of thrombin adsorbed on the peptide surfaces was inhibited, and inhibition was greatest on the Cys-(D)Phe-Pro-Arg surface. We concluded that the peptide surfaces may have potential as antithrombogenic materials via their ability to scavenge and inhibit thrombin generated as a result of blood-material contact.

Inflammatory cell recruitment, distribution, and chemiluminescence response at IgG precoated- and thiol functionalized gold surfaces

The role of complement activation by artificial surfaces relative to inflammatory response is not well understood. This study was performed to evaluate the inflammatory cell recruitment, distribution, and ex vivo metabolic activation of surfaces with different plasma protein adsorption and complement activation properties in vitro. The implants were (1) pure gold (reference), (2) albumin-precoated (3) IgG-precoated gold, and (4) 3-mercapto-1, 2-propanediol [mercaptoglycerol (MG)] and (5) glutathione (GSH) immobilized to gold. The implant disks were inserted subcutaneously in rats for 24 h, and the number of inflammatory cells that were recruited to the implant adjacent to the surrounding fluid phase (exudate) and the surfaces were quantified by DNA measurements. The oxidative burst was analyzed ex vivo using spontaneous and phorbol myristate acetate (PMA)-stimulated, luminol-enhanced chemiluminescence (CL). The in vitro surface-induced anti-rat C3 binding was evaluated by ellipsometry and antibody techniques after plasma incubations for 1 and 30 min. The ellipsometric results showed that immobilized mercaptoglycerol and IgG-coated, but not the immobilized glutathione or the reference Au, bound anti-C3. The in vivo results revealed that the largest amount of cells was associated with the IgG-coated surfaces, followed by immobilized GSH and MG, albumin-coated, and gold surfaces, respectively. No spontaneous ex vivo luminol-enhanced CL was recorded from the cells irrespective of surface functionality or localization. A down-regulation of surface-associated and exudate leukocyte CL was observed ex vivo, irrespective of surface functionality. The results do not indicate a clear relationship between the degree of complement activation in vitro and leukocyte recruitment and adhesion in vivo for differently functionalized surfaces.

In vivo cell recruitment, cytokine release and chemiluminescence response at gold, and thiol functionalized surfaces

Hydroxylated and methylated surfaces were prepared by the self-assembled monolayer technique (SAM) of alkane thiols on gold. The surfaces were used to evaluate the influence of implant surface chemistry on protein deposition and inflammatory cell response. Implants were inserted subcutaneously in the rat for 3 and 24 h. The surface chemical properties influenced the in vitro rat plasma protein adsorption (ellipsometry/antibody) with few exceptions (albumin not found and fibrinogen always found). The number of recruited cells and their distribution (DNA from implant versus from exudate) was influenced by the different chemistries at 24 h, but not at 3 h. HIS48+, ED1+, ED2+ and small numbers of CD5+ cells were present in the exudate at both time periods (flow cytometry). The cellular oxidative metabolism was low, although cells on -OH surfaces responded with the highest phorbol ester-stimulated chemiluminescence (CL)/DNA. The levels of cytokines IL-1alpha, IL-1beta and TNFalpha (ELISA) were not influenced by material surface chemistry. Sham operated sites had a higher cytokine concentration/DNA compared with exudates from an implant milieu. The results of this study show that surface chemical functionalization modifies specific events in the inflammatory response around implants in soft tissues.

Ellipsometric studies in vitro on kinetics of rat complement activation

The role of complement activation may be important during the early interactions between implantable materials and blood and during the acute inflammatory phase, but it is not well understood. This applies especially to rats that are extensively used in in vivo animal models for materials and surface testing. Features of the kinetics of rat complement activation were studied and compared with human complement by the ellipsometry and antibody techniques. The results indicate that the rat classical pathway is rapidly activated, but it is not as fast as the human system. The activation of the alternative pathway was observed within 5 min in the rat system and within 15 min for the human. Thus, the observations indicate substantial differences in the kinetics between the two species. This may influence the choice of the rat experimental model and the tissue response to materials during in vivo conditions.

Complement activation and inflammation triggered by model biomaterial surfaces

Biomaterial-mediated complement activation repeatedly has been invoked as a trigger of phagocyte reactions and inflammation. However, a direct correlation between complement activation and inflammatory responses to biomaterial surfaces has yet to be established. Using an animal implantation model and gold surfaces bearing various thiol-linked functionalities, we investigated the potency of different surface groups in prompting complement activation in vitro and surface-mediated accumulation of inflammatory cells in vivo. Among the surfaces tested, mercaptoglycerol- and mercaptoethanol-bearing surfaces engendered the strongest inflammatory responses, as reflected by the accumulation of large numbers of adherent neutrophils and monocytes/macrophages. In contrast, L-cysteine-coated surfaces caused only minor inflammatory responses, and both glutathione-modified and untreated gold implants attracted minimal numbers of inflammatory cells. The accumulation of inflammatory cells on mercaptoglycerol surfaces appears to arise from surface-mediated complement activation because complement-depleted animals failed to exhibit inflammatory responses to mercaptoglycerol-modified implants. Furthermore, there is a close relationship between surface-mediated complement activation (as measured by in vitro iC3b/C5b-9 generation and C3 deposition) and in vivo inflammatory responses. At least in this animal model and with these model surfaces, our results indicate that surface-mediated complement activation can be responsible for the subsequent accumulation of inflammatory cells on implant surfaces.