Distinct Polymer Architecture Mediates Switching of Complement Activation Pathways at the Nanosphere−Serum Interface: Implications for Stealth Nanoparticle Engineering

Abstract

Nanoparticles with surface projected polyethyleneoxide (PEO) chains in "mushroom؊brush" and "brush" configurations display stealth properties in systemic circulation and have numerous applications in sitespecific targeting for controlled drug delivery and release as well as diagnostic imaging. We report on the "structure؊activity" relationship pertaining to surface-immobilized PEO of various configurations on model nanoparticles, and the initiation of complement cascade, which is the most ancient component of innate human immunity, and its activation may induce clinically significant adverse reactions in some individuals. Conformational states of surface-projected PEO chains, arising from the block copolymer poloxamine 908 adsorption, on polystyrene nanoparticles trigger complement activation differently. Alteration of copolymer architecture on nanospheres from mushroom to brush configuration not only switches complement activation from C1q-dependent classical to lectin pathway but also reduces the level of generated complement activation products C4d, Bb, C5a, and SC5b-9. Also, changes in adsorbed polymer configuration trigger alternative pathway activation differently and through different initiators. Notably, the role for properdin-mediated activation of alternative pathway was only restricted to particles displaying PEO chains in a transition mushroom؊brush configuration. Since nanoparticle-mediated complement activation is of clinical concern, our findings provide a rational basis for improved surface engineering and design of immunologically safer stealth and targetable nanosystems with polymers for use in clinical medicine.

Harnessing Nanoparticles for Immune Modulation

“…Like, PEG, PEO forms a mushroom-or brush-like configuration on the surface of NPs. Unlike PEG, however, PEO may activate the C1q-dependent complement pathway in its mushroom-like configuration, whereas the brush-like configuration can trigger the lectin-specific complement cascade [44]. Interestingly, although NP coatings may prolong NP serum half-life, cells of the MPS still appear to be involved in the primary clearance mechanism for intravenously infused NPs [43].…”

Biomolecular coronas provide the biological identity of nanosized materials

“…While surface modifications (such as PEGylation 39 ) reduce the binding of additional biomolecules, some association of biomolecules may still occur 35,40 . Their presence may lead to more subtle and poorly understood biological consequences, issues possibly related to current struggles in achieving efficient targeting of nanomedicines in vivo.…”

The role of PEG conformation in mixed layers: from protein corona substrate to steric stabilization avoiding protein adsorption

“…The possibility of tuning the adsorption of proteins is also described here. This might have consequences in determining the final fate of NPs in organisms since important processes such as cell uptake [48] or activation of the complement systems are known to be influenced by the adsorption of proteins [11]. Last but not least, a properly designed mixed layer gives the opportunity to tune both functionality and stability of the NPs.…”

“…This has strong consequences on the design of NPs for medicine. For example, a different degree and type of complement activation, which ultimately depends on the recognition of the conjugates by specific proteins, was directly correlated with the conformation of the PEO monolayer on polymeric NPs in a recent work [11]. Briefly, Hamad et al showed that the complement activation was dramatically reduced for the nanospheres which have PEO chains in the brush conformation.…”

“…This is the case of stealthing with the FDA-approved polymer polyethylene glycol (PEG) [8][9][10]. After the simple, but widely exploited, use of PEG as surfactant for NPs (just by adding it in excess), many efforts are now being carried out unveiling the mechanism of action and to properly characterize these nanosystems to achieve a better control over physicochemical properties such as colloidal stability at working conditions or interactions with proteins [6,[10][11][12][13]. This is of special interest in environments where high ionic strength solutions, such as the biological fluids (e.g.…”