Activation of the complement system by polysaccharidic surfaces bearing carboxymethyl, carboxymethylbenzylamide and carboxymethylbenzylamide sulphonate groups

Carbazate-modified cross-linked dextran microparticles suppress the progression of osteoarthritis by ROS scavenging

A series of modified polysaccharide microparticles have been fabricated and their potential application for scavenging reactive oxygen species (ROS) and their derivatives to achieve osteoarthritis (OA) treatment has been explored. These microparticles were cross-linked dextran (Sephadex) with different carbazate substitution ratios determined by the TNBS assay and elemental analysis. It has been demonstrated that they could effectively scavenge carbonylated proteins and ROS including hydroxyl radicals (˙OH), superoxide anions (˙O₂^-) and H₂O₂ and their derivatives with high efficiency, improve the viability of H₂O₂-treated chondrocytes by reducing their ROS levels, as well as lower their inflammatory factors. The above ability of antioxidation and inflammation resistance improved with the increase of carbazate substitution ratio. Significantly, this work provided the proof that modified Sephadex successfully alleviated the deterioration of cartilage and the progression of OA in vivo. The proposed microparticles showed a very promising capability for reducing ROS levels and further treating OA.

Hemocompatibility of Degrading Polymeric Biomaterials: Degradable Polar Hydrophobic Ionic Polyurethane versus Poly(lactic-co-glycolic) Acid

The use of degradable polymers in vascular tissue regeneration has sparked the need to characterize polymer biocompatibility during degradation. While tissue compatibility has been frequently addressed, studies on polymer hemocompatibility during degradation are limited. The current study evaluated the differences in hemocompatibility (platelet response, complement activation, and coagulation cascade initiation) between as-made and hydrolyzed poly(lactic-co-glycolic) acid (PLGA) and degradable polar hydrophobic ionic polyurethane (D-PHI). Platelet activation decreased (in whole blood) and platelet adhesion decreased (in blood without leukocytes) for degraded versus as-made PLGA. D-PHI showed minimal hemocompatibility changes over degradation. Leukocytes played a major role in mediating platelet activation for samples and controls, as well as influencing platelet-polymer adhesion on the degraded materials. This study demonstrates the importance of assessing the blood compatibility of biomaterials over the course of degradation since the associated changes in surface chemistry and physical state could significantly change biomaterial hemocompatibility.

Interactions of organic nanoparticles with proteins in physiological conditions

The efficacy of nanoparticles in biomedical applications is strongly influenced by their ability to bind proteins onto their surface. The analysis of organic nanoparticles interacting with proteins in physiological conditions may help in the successful design of next generation nanoparticles with improved biodistributions and therapeutic performances.

Interaction between non-specific electrostatic forces and humoral factors in haemocyte attachment and encapsulation in the edible cockle, Cerastoderma edule

In invertebrates, encapsulation is the common immune defence reaction towards foreign bodies, including multicellular parasites, which enter the haemocoel and are too large to be phagocytosed. This immune response has been most extensively studied in insects, in which it is highly complex, involving a diversity of cellular and molecular processes, but little is known of this process in bivalve molluscs. Non-specific physicochemical properties are known to influence parasite-haemocyte interactions in many invertebrates, and these may provide the common basis of encapsulation on which highly specific biochemical interactions are imposed. The present study uses synthetic beads and thread to mimic inactive metacercarial cysts of trematodes, and thus investigates factors involved in the basic, non-specific mechanisms of cell attachment and encapsulation in the edible cockle, Cerastoderma edule. Results showed that positively charged targets stimulated the most vigorous response, and further detailed experiments revealed that non-specific electrostatic forces and humoral plasma factors have a synergistic role in haemocyte attachment and the encapsulation response of C. edule.

Influence of polysaccharide coating on the interactions of nanoparticles with biological systems

Since dextran (DEX) grafted with poly(epsilon-caprolacton) (PCL) side chains (PCL-DEX) copolymers could form nanoparticles with a well defined core-shell structure, we investigated the ability of the DEX coating to modify the interactions with the biological media. We first studied the influence of the DEX coating on the phagocytosis of the nanoparticles by human TPH-1 and J774 murine macrophage-like cell lines. Then, the activation of the complement system (CH50 measurement) at the surface of the particles and the adsorption of plasma proteins (2D-PAGE) were investigated, too. It was found that the modification of the surface with DEX significantly reduced the cytotoxicity towards J774 macrophages: the IC50 was increased from 10 to 600 microg/ml. However, the DEX coating could activate complement, probably due to a loop-like conformation of DEX similar to that of cross-linked DEX in Sephadex (a strong complement activator). In addition, depending on whether the DEX loops were large or compact, preferential adsorption, apolipoproteins or immunoglobulins, was observed.

Complement activation by model drug carriers for intravenous application: determination by two-dimensional electrophoresis

The interactions of intravenously injected drug carriers with blood proteins are considered as an important factor for the fate of the particles after their administration. Protein adsorption on latex particles applied as model for intravenous drug carriers was analysed using two-dimensional electrophoresis (2-DE). The particles were incubated in citrated plasma, serum and heat-inactivated serum, respectively. Incubation in the various media resulted in clear differences in the protein adsorption patterns. Two characteristic protein spots were determined to be enriched on the 2-DE gels only after incubation of the particles in serum. Employing N-terminal microsequencing these protein spots were identified to be fragments of the complement protein C3. Enrichment of these particular spots was most likely a result of complement activation by the particles. Mechanism of C3 binding to the particle surface and subsequent inactivation by cleavage are discussed in order to explain the results. It could be demonstrated that 2-DE analysis provides the possibility to distinguish between adsorption and covalent attachment of C3 to particulate surfaces. The findings indicate that complement activation was caused by covalent binding of the C3 component C3b to the particles' surface. The influence of the incubation medium on the in vitro protein adsorption of particulate drug carriers has to be considered when a correlation between the protein adsorption pattern and the in vivo behaviour of the particles is approached.

Cellulose carbamates and derivatives as hemocompatible membrane materials for hemodialysis

Dialysis membranes made from regenerated cellulose are under dispute because of their alleged lack of hemocompatibility. The introduction of membranes from synthetically modified cellulose, like cellulose acetate or Hemophan, has proven, however, that hemocompatible membranes can be fabricated from cellulose by means of chemical surface modifications. In addition to membranes made from modified cellulose like ethers or esters, which were investigated in earlier experiments, we looked for further cellulose modifications to be assessed for their hemocompatibility. For this purpose, we synthesized a series of cellulose carbamate derivatives to profit from the excellent hemocompatibility pattern of the urethane family. In vitro investigations on membranes made from these cellulose modifications proved a direct relationship between the degree of modification and hemocompatibility. This was proven for the following 3 representative hemocompatibility parameters: complement C5a generation, thrombin-antithrombin (TAT) III formation, and platelet count (PC). As already shown for modifications made from cellulose esters, a direct dependency between improved hemocompatibility and the degree of substitution (DS) in the cellulose molecule could be found. In our experiments, a degree of substitution below a value of 0.1 led to a nearly complete suppression of complement activation for all cellulose carbamates under investigation. In contrast to data on cellulose esters, we observed that molecular weight or molecular conformation of chemical substituents exerted only a minor effect on the hemocompatibility pattern. In addition, data on cellulose carbamate esters (e.g., cellulose succinate-phenyl-carbamate) show that a simultaneous but balanced substitution with hydrophilic and hydrophobic groups at the surface of the cellulose polymer is a further prerequisite for optimal hemocompatibility. It seems that the carbamate configuration per se has a positive effect on the hemocompatibility pattern of synthetically modified cellulose membranes.

The role of surface characteristics in eliciting humoral encapsulation of foreign bodies in Plasmodium-refractory and -susceptible strains of Anopheles gambiae

A refractory strain of the mosquito, Anopheles gambiae, melanotically encapsulates and kills many species of malaria parasites, whereas susceptible strains allow the parasites to develop normally. To study the role of surface characteristics in eliciting this immune response, 27 types of chromatography beads that differed in matrix type, charge, functional group, and functional group density were assayed for degree of melanotic encapsulation in refractory and susceptible mosquitoes. Overall, two glucan-based matrices, Sephadex (dextran) and cellulose, stimulated the strongest responses, regardless of functional group. Substituting matrix hydroxyl groups with functional groups on Sephadex and cellulose beads decreased the level of encapsulation. These results demonstrate that glucans induce melanotic encapsulation in An. gambiae. Beads with agarose, polystyrene, and acrylic matrices, and most methacrylate-based beads elicited little or no melanization; however, epoxide-methacrylate beads were encapsulated, demonstrating that glucans are not essential for eliciting a response. Comparisons between the two strains demonstrated that refractory mosquitoes melanized many bead types to a greater degree than did susceptible mosquitoes. On this basis, we propose that an important difference between the two strains is that one of the enzymes involved in the melanization pathway functions at a higher level in the refractory strain. Finally, of all beads tested, only 85% substituted CM-Sephadex beads were virtually unmelanized in susceptible mosquitoes but highly melanized in the refractory strain; thus, a specific surface microenvironment is necessary to demonstrate this effect.

Interactions of nanoparticles bearing heparin or dextran covalently bound to poly(methyl methacrylate) with the complement system

The efficient uptake of injected nanoparticles by cells of the mononuclear phagocyte system (MPS) limits the development of long-circulating colloidal drug carriers. The complement system plays a major role in the opsonization and recognition processes of foreign materials. Since heparin is an inhibitor of complement activation, nanoparticles bearing heparin covalently bound to poly(methyl methacrylate) (PMMA) have been prepared and their interactions with complement evaluated. The particles retained the complement-inhibiting properties of soluble heparin. Nanoparticles bearing covalently bound dextran instead of heparin were weak activators of complement as compared with crosslinked dextran (Sephadex) or bare PMMA nanoparticles. In addition to the specific activity of bound heparin, the protective effect of both polysaccharides is hypothesized to be due to the presence of a dense brush-like layer on the surface of the particles. Such properties are expected to reduce the uptake by MPS in vivo.

Effect of PEO surface density on long-circulating PLA-PEO nanoparticles which are very low complement activators

The rapid uptake of injected nanoparticles by cells of the mononuclear phagocytes system (MPS) is a major obstacle when a long blood circulation time is needed. Whereas nanoparticles made from PLA and stabilized by surfactants (PLA-F68) are rapidly phagocytized, the rate of phagocytosis is strongly reduced in case of nanoparticles made from a diblock copolymer (PLA-PEO). Because of the role of the complement system in opsonization, this difference of phagocytosis was hypothesized to be related to this system. An important complement consumption was obtained in 5 min in the presence of PLA-F68 particles. In the presence of a higher surface area of PLA-PEO particles possessing a high PEO surface density, the consumption remained very low. When the average PEO surface density was decreased on such particles below a given threshold, a fast and strong complement consumption occurred again. These experimental data support the concept of steric repulsion towards proteins, by surfaces covered with terminally attached PEO chains and emphasize the prime importance of PEO surface density in such an effect. The major, but probably not exclusive, role of complement as an opsonin capable of inducing a fast phagocytosis by MPS should be taken into account concerning the in vitro evaluation of nanoparticles as candidates for a long blood circulation.