Activation of Human Complement System by Dextran-Coated Iron Oxide Nanoparticles Is Not Affected by Dextran/Fe Ratio, Hydroxyl Modifications, and Crosslinking

Nanoparticle-Binding Immunoglobulins Predict Variable Complement Responses in Healthy and Diseased Cohorts

Systemic administration of nanomedicines results in the activation of the complement cascade, promoting phagocytic uptake and triggering proinflammatory responses. Identifying the biomarkers that can predict the "risk" of abnormally high complement responders can improve the safety and efficacy of nanomedicines. Polyethylene glycol (PEG) and dextran are two types of clinically approved polymer coatings that trigger complement activation. We performed a multifaceted analysis of the factors affecting the complement activation by PEGylated liposomal doxorubicin (PLD) and dextran-coated superparamagnetic iron oxide nanoworms (SPIO NWs) in plasma from patients with different inflammatory disease conditions and healthy donors. The complement activation (measured as deposition of the complement protein C3) varied greatly, with 29-fold and 26-fold differences for PLD and SPIO NWs, respectively. Chronic inflammation, acute infection, use of steroids, and sex had minor effects on the variable complement activation, whereas age inversely correlated with the complement activation. C-reactive protein level was not predictive of high (top 20th percentile) complement responses. Plasma concentrations of the main complement factors, as well as total IgG and IgM, showed no correlation with the activation by either nanoparticle. On the other hand, plasma concentrations of anti-PEG IgG and IgM showed a strong positive correlation with the activation by PLD. Particularly, titers of anti-PEG IgM showed the best predictive value for the "risk" of high complement activation by PLD. Titers of antidextran IgG and IgM showed a lower correlation with the activation by SPIO NWs and poor predictive value of the top 20% complement responses. Nanoparticle-bound immunoglobulins showed the best correlation with complement activation and a strong predictive value, supporting the critical role of immunoglobulins in inciting complement. The opsonization of PLD with C3 in plasma with high anti-PEG antibodies was predominantly via the alternative pathway. Characterizing the nature of nanoparticle-binding antibodies has important implications in mitigating and stratifying nanomedicine safety.

Validation of dot blot immunoassay for measurement of complement opsonization of nanoparticles

Complement plays a critical role in the immune response toward nanomaterials. The complement attack on a foreign surface results in the deposition of C3, assembly of C3 convertases, the release of anaphylatoxins C3a and C5a, and finally, the formation of membrane attack complex C5b-9. Various technologies can measure complement activation markers in the fluid phase, but measurements of surface C3 deposition are less common. Previously, we developed an ultracentrifugation-based dot blot immunoassay (DBI) to measure the deposition of C3 and other protein corona components on nanoparticles. Here, we validate the repeatability of the DBI and its correlation with pathway-specific and common fluid phase markers. Moreover, we discuss the advantages of DBI, such as cost-effectiveness and versatility, while addressing potential limitations. This study provides insights into complement activation at the nanosurface level, offering a valuable tool for nanomedicine researchers in the field.

Accumulation of Iron Oxide-Based Contrast Agents in Rabbit Atherosclerotic Plaques in Relation to Plaque Age and Vulnerability Features

Purpose

In this study, a detailed characterization of a rabbit model of atherosclerosis was performed to assess the optimal time frame for evaluating plaque vulnerability using superparamagnetic iron oxide nanoparticle (SPION)-enhanced magnetic resonance imaging (MRI).

Methods

The progression of atherosclerosis induced by ballooning and a high-cholesterol diet was monitored using angiography, and the resulting plaques were characterized using immunohistochemistry and histology. Morphometric analyses were performed to evaluate plaque size and vulnerability features. The accumulation of SPIONs (novel dextran-coated SPIONDex and ferumoxytol) in atherosclerotic plaques was investigated by histology and MRI and correlated with plaque age and vulnerability. Toxicity of SPIONDex was evaluated in rats.

Results

Weak positive correlations were detected between plaque age and intima thickness, and total macrophage load. A strong negative correlation was observed between the minimum fibrous cap thickness and plaque age as well as the mean macrophage load. The accumulation of SPION in the atherosclerotic plaques was detected by MRI 24 h after administration and was subsequently confirmed by Prussian blue staining of histological specimens. Positive correlations between Prussian blue signal in atherosclerotic plaques, plaque age, and macrophage load were detected. Very little iron was observed in the histological sections of the heart and kidney, whereas strong staining of SPIONDex and ferumoxytol was detected in the spleen and liver. In contrast to ferumoxytol, SPIONDex administration in rabbits was well tolerated without inducing hypersensitivity. The maximum tolerated dose in rat model was higher than 100 mg Fe/kg.

Conclusion

Older atherosclerotic plaques with vulnerable features in rabbits are a useful tool for investigating iron oxide-based contrast agents for MRI. Based on the experimental data, SPIONDex particles constitute a promising candidate for further clinical translation as a safe formulation that offers the possibility of repeated administration free from the risks associated with other types of magnetic contrast agents.

Inhibition of acute complement responses towards bolus-injected nanoparticles using targeted short-circulating regulatory proteins

Effective inhibition of the complement system is needed to prevent the accelerated clearance of nanomaterials by complement cascade and inflammatory responses. Here we show that a fusion construct consisting of human complement receptor 2 (CR2) (which recognizes nanosurface-deposited complement 3 (C3)) and complement receptor 1 (CR1) (which blocks C3 convertases) inhibits complement activation with picomolar to low nanomolar efficacy on many types of nanomaterial. We demonstrate that only a small percentage of nanoparticles are randomly opsonized with C3 both in vitro and in vivo, and CR2-CR1 immediately homes in on this subpopulation. Despite rapid in vivo clearance, the co-injection of CR2-CR1 in rats, or its mouse orthologue CR2-Crry in mice, with superparamagnetic iron oxide nanoparticles nearly completely blocks complement opsonization and unwanted granulocyte/monocyte uptake. Furthermore, the inhibitor completely prevents lethargy caused by bolus-injected nanoparticles, without inducing long-lasting complement suppression. These findings suggest the potential of the targeted complement regulators for clinical evaluation.

PEN-coated superparamagnetic iron-mediated delivery of siSnail2 to inhibit metastasis and promote ferroptosis in the treatment of cancer

Cancer represents a significant global public health challenge, and conventional cancer therapies such as surgery and chemoradiotherapy are not enough due to the increased complexity of cancer. Nanotechnology has the potential to revolutionize tumor treatments by integrating gene therapy, tumor targeting, and drug delivery. In this study, we demonstrated that Snail2 plays a crucial role in the migration and invasion of lung and liver carcinoma. We proposed a novel approach to synergize the aminated crosslinking dextran coat of superparamagnetic iron oxide nano worms (CLIO-NH2, CN) with small interfering Snail2 RNA (siSnail2). The efficiency of siSnail2 delivery was significantly improved by coating CN with N-Isopropylacrylamide-modified polyethylenimine (CNP). In vitro, experiments revealed that CNP@siSnail2 effectively inhibited cancer cell EMT, migration, and invasion. Moreover, CNP@ siSnail2 promoted cancer cell death through various mechanisms, including apoptosis and ferroptosis. The combination of CNP@ siSnail2 and cisplatin significantly improved the anti-tumor effect of the treatment. Animal models demonstrated that the combined treatment of CNP@ siSnail2 and cisplatin resulted in excellent tumor inhibition effects. Our findings provide a potential combined treatment strategy for cancer therapy.

Nanoparticle-induced immune response: Health risk versus treatment opportunity?

Nanoparticles (NPs) are not only employed in many biomedical applications in an engineered form, but also occur in our environment, in a more hazardous form. NPs interact with the immune system through various pathways and can lead to a myriad of different scenarios, ranging from their quiet removal from circulation by macrophages without any impact for the body, to systemic inflammatory effects and immuno-toxicity. In the latter case, the function of the immune system is affected by the presence of NPs. This review describes, how both the innate and adaptive immune system are involved in interactions with NPs, together with the models used to analyse these interactions. These models vary between simple 2D in vitro models, to in vivo animal models, and also include complex all human organ on chip models which are able to recapitulate more accurately the interaction in the in vivo situation. Thereafter, commonly encountered NPs in both the environment and in biomedical applications and their possible effects on the immune system are discussed in more detail. Not all effects of NPs on the immune system are detrimental; in the final section, we review several promising strategies in which the immune response towards NPs can be exploited to suit specific applications such as vaccination and cancer immunotherapy.

Comparative in vitro and in vivo Evaluation of Different Iron Oxide-Based Contrast Agents to Promote Clinical Translation in Compliance with Patient Safety

Introduction

One of the major challenges in the clinical translation of nanoparticles is the development of formulations combining favorable efficacy and optimal safety. In the past, iron oxide nanoparticles have been introduced as an alternative for gadolinium-containing contrast agents; however, candidates available at the time were not free from adverse effects.

Methods

Following the development of a potent iron oxide-based contrast agent SPION^Dex, we now performed a systematic comparison of this formulation with the conventional contrast agent ferucarbotran and with ferumoxytol, taking into consideration their physicochemical characteristics, bio- and hemocompatibility in vitro and in vivo, as well as their liver imaging properties in rats.

Results

The results demonstrated superior in vitro cyto-, hemo- and immunocompatibility of SPION^Dex in comparison to the other two formulations. Intravenous administration of ferucarbotran or ferumoxytol induced strong complement activation-related pseudoallergy in pigs. In contrast, SPION^Dex did not elicit any hypersensitivity reactions in the experimental animals. In a rat model, comparable liver imaging properties, but a faster clearance was demonstrated for SPION^Dex.

Conclusion

The results indicate that SPION^Dex possess an exceptional safety compared to the other two formulations, making them a promising candidate for further clinical translation.

Quantitative comparison of the protein corona of nanoparticles with different matrices

Nanoparticles (NPs) are paving the way for improved treatments for difficult to treat diseases diseases; however, much is unknown about their fate in the body. One important factor is the interaction between NPs and blood proteins leading to the formation known as the “protein corona” (PC). The PC, consisting of the Hard (HC) and Soft Corona (SC), varies greatly based on the NP composition, size, and surface properties. This highlights the need for specific studies to differentiate the PC formation for each individual NP system. This work focused on comparing the HC and SC of three NPs with different matrix compositions: a) polymeric NPs based on poly(lactic-co-glycolic) acid (PLGA), b) hybrid NPs consisting of PLGA and Cholesterol, and c) lipidic NPs made only of Cholesterol. NPs were formulated and characterized for their physico-chemical characteristics and composition, and then were incubated in human plasma. In-depth purification, identification, and statistical analysis were then performed to identify the HC and SC components. Finally, similar investigations demonstrated whether the presence of a targeting ligand on the NP surface would affect the PC makeup. These results highlighted the different PC fingerprints of these NPs, which will be critical to better understand the biological influences of the PC and improve future NP designs.

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NPs with different matrices were formulated: PLGA, Cholesterol, or mixed PLGA-Chol hybrids.

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The hard and soft corona of each formulation was quantified and compared.

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The PC seems to be more strongly affected by the polymer rather than the lipid in mixed NPs.

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The soft corona depends more on the hard corona composition than on the matrix.

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Surface modification with a targeting ligand did not influence PC composition.

Antibody-Dependent Complement Responses toward SARS-CoV-2 Receptor-Binding Domain Immobilized on "Pseudovirus-like" Nanoparticles

Many aspects of innate immune responses to SARS viruses remain unclear. Of particular interest is the role of emerging neutralizing antibodies against the receptor-binding domain (RBD) of SARS-CoV-2 in complement activation and opsonization. To overcome challenges with purified virions, here we introduce "pseudovirus-like" nanoparticles with ∼70 copies of functional recombinant RBD to map complement responses. Nanoparticles fix complement in an RBD-dependent manner in sera of all vaccinated, convalescent, and naı̈ve donors, but vaccinated and convalescent donors with the highest levels of anti-RBD antibodies show significantly higher IgG binding and higher deposition of the third complement protein (C3). The opsonization via anti-RBD antibodies is not an efficient process: on average, each bound antibody promotes binding of less than one C3 molecule. C3 deposition is exclusively through the alternative pathway. C3 molecules bind to protein deposits, but not IgG, on the nanoparticle surface. Lastly, "pseudovirus-like" nanoparticles promote complement-dependent uptake by granulocytes and monocytes in the blood of vaccinated donors with high anti-RBD titers. Using nanoparticles displaying SARS-CoV-2 proteins, we demonstrate subject-dependent differences in complement opsonization and immune recognition.

Getting to the Core of It All: Nanocapsules to Mitigate Infusion Reactions Can Promote Hemostasis and Be a Platform for Intravenous Therapies

One of the significant challenges to translation of intravenously administered nanomaterials has been complement-mediated infusion reactions which can be lethal. Slow infusions can reduce infusion reactions, but slow infusions are not always possible in applications like controlling bleeding following trauma. Thus, avoiding complement activation and infusion responses is essential to manage bleeding. We identified nanocapsules based on polyurethane as candidates that did not activate C5a and explored their PEGylation and functionalization with the GRGDS peptide to create a new class of hemostatic nanomaterials. Using the clinically relevant rotational thromboelastography (ROTEM), we determined that nanocapsules promote faster clotting than controls and maintain the maximum clot firmness, which is critical for reducing bleeding. Excitingly, these polyurethane-based nanocapsules did not activate complement or the major pro-inflammatory cytokines. This work provides critical evidence for the role of modulating the core material in developing safer nanomedicines for intravenous applications.

The ancillary effects of nanoparticles and their implications for nanomedicine

Nanoparticles are often engineered as a scaffolding system to combine targeting, imaging and/or therapeutic moieties into a unitary agent. However, mostly overlooked, the nanomaterial itself interacts with biological systems exclusive of application-specific particle functionalization. This nanoparticle biointerface has been found to elicit specific biological effects, which we term 'ancillary effects'. In this Review, we describe the current state of knowledge of nanobiology gleaned from existing studies of ancillary effects with the objectives to describe the potential of nanoparticles to modulate biological effects independently of any engineered function; evaluate how these effects might be relevant for nanomedicine design and functional considerations, particularly how they might be useful to inform clinical decision-making; identify potential clinical harm that arises from adverse nanoparticle interactions with biology; and, finally, highlight the current lack of knowledge in this area as both a barrier and an incentive to the further development of nanomedicine.

Complement opsonization of nanoparticles: Differences between humans and preclinical species

The complement system plays a key role in opsonization and immune clearance of engineered nanoparticles. Understanding the efficiency, inter-subject, and inter-strain differences of complement opsonization in preclinical species can help with translational nanomedicine development and improve our ability to model complement response in humans. Dextran-coated superparamagnetic iron oxide (SPIO) nanoparticles and a wide range of non-magnetic iron oxide nanoparticle formulations are widely used in magnetic resonance imaging and as clinically approved iron supplements. Previously we found that opsonization of SPIO nanoworms (NW) with the third complement protein (C3) proceeds mostly via the alternative pathway in humans, and via the lectin pathway in mice. Here, we studied the pathway and efficiency of opsonization of 106 nm SPIO NW with C3 in different preclinical species and commonly used laboratory strains. In sera of healthy human donors (n = 6), C3 opsonization proceeded exclusively through the alternative pathway. On the other hand, the C3 opsonization in dogs (6 breeds), rats (4 strains) and mice (5 strains) sera was either partially or completely dependent on the complement Ca²⁺-sensitive pathways (lectin and/or classical). Specifically, C3 opsonization in sera of Long Evans rat strain, and mouse strains widely used in nanomedicine research (BALB/c, C57BL/6 J, and A/J) was only through the Ca²⁺-dependent pathways. Dogs and humans had the highest between-subject variability in C3 opsonization levels, while rat and mouse sera showed the lowest between-strain variability. Furthermore, using a panel of SPIO nanoparticles of different sizes and dextran coatings, we found that the level of C3 opsonization (C3 molecules per milligram Fe) in human sera was lower than in animal sera. At the same time, there was a strong predictive value of complement opsonization in dog and rat sera; nanoparticles with higher C3 deposition in animals showed higher deposition in humans, and vice versa. Notably, the opsonization decreased with decreasing size in all sera. The studies highlight the importance of the consideration of species and strains for predicting human complement responses (opsonization) towards nanomedicines.

In vivo Cell Tracking Using Non-invasive Imaging of Iron Oxide-Based Particles with Particular Relevance for Stem Cell-Based Treatments of Neurological and Cardiac Disease

Stem cell-based therapeutics is a rapidly developing field associated with a number of clinical challenges. One such challenge lies in the implementation of methods to track stem cells and stem cell-derived cells in experimental animal models and in the living patient. Here, we provide an overview of cell tracking in the context of cardiac and neurological disease, focusing on the use of iron oxide-based particles (IOPs) visualized in vivo using magnetic resonance imaging (MRI). We discuss the types of IOPs available for such tracking, their advantages and limitations, approaches for labeling cells with IOPs, biological interactions and effects of IOPs at the molecular and cellular levels, and MRI-based and associated approaches for in vivo and histological visualization. We conclude with reviews of the literature on IOP-based cell tracking in cardiac and neurological disease, covering both preclinical and clinical studies.

Methodological needs in the quality and safety characterisation of nanotechnology-based health products: Priorities for method development and standardisation

Nanotechnology-based health products are providing innovative solutions in health technologies and the pharmaceutical field, responding to unmet clinical needs. However, suitable standardised methods need to be available for quality and safety assessments of these innovative products prior to their translation into the clinic and for monitoring their performance when manufacturing processes are changed. The question arises which technological solutions are currently available within the scientific community to support the requested characterisation of nanotechnology-based products, and which methodological developments should be prioritized to support product developers in their regulatory assessment. To this end, the work presented here explored the state-of-the-art methods to identify methodological gaps associated with the preclinical characterisation of nanotechnology-based medicinal products and medical devices. The regulatory information needs, as expressed by regulatory authorities, were extracted from the guidance documents released so far for nanotechnology-based health products and mapped against available methods, thus allowing an analysis of methodological gaps and needs. In the first step, only standardised methods were considered, leading to the identification of methodological needs in five areas of characterisation, including: (i) surface properties, (ii) drug loading and release, (iii) kinetic properties in complex biological media, (iv) ADME (absorption, distribution, metabolism and excretion) parameters and (v) interaction with blood and the immune system. In the second step, a detailed gap analysis included analytical approaches in earlier stages of development, and standardised test methods from outside of the nanotechnology field that could address the identified areas of gaps. Based on this analysis, three categories of methodological needs were identified, including (i) method optimisation/adaptation to nanotechnological platforms, (ii) method validation/standardisation and (iii) method development for those areas where no technological solutions currently exist. The results of the analysis presented in this work should raise awareness within the scientific community on existing and emerging methodological needs, setting priorities for the development and standardisation of relevant analytical and toxicological methods allowing the development of a robust testing strategy for nanotechnology-based health products.

Nanostrategies to Develop Current Antiviral Vaccines

Infectious diseases are a worldwide concern. They are responsible for increasing the mortality rate and causing economic and social problems. Viral epidemics and pandemics, such as the COVID-19 pandemic, force the scientific community to consider molecules with antiviral activity. A number of viral infections still do not have a vaccine or efficient treatment and it is imperative to search for vaccines to control these infections. In this context, nanotechnology in association with the design of vaccines has presented an option for virus control. Nanovaccines have displayed an impressive immune response using a low dosage. This review aims to describe the advances and update the data in studies using nanovaccines and their immunomodulatory effect against human viruses.

Insights into colloidal nanoparticle-protein corona interactions for nanomedicine applications

Colloidal nanoparticles (NPs) have attracted significant attention due to their unique physicochemical properties suitable for diagnosing and treating different human diseases. Nevertheless, the successful implementation of NPs in medicine demands a proper understanding of their interactions with the different proteins found in biological fluids. Once introduced into the body, NPs are covered by a protein corona (PC) that determines the biological behavior of the NPs. The formation of the PC can eventually favor the rapid clearance of the NPs from the body before fulfilling the desired objective or lead to increased cytotoxicity. The PC nature varies as a function of the different repulsive and attractive forces that govern the NP-protein interaction and their colloidal stability. This review focuses on the phenomenon of PC formation on NPs from a physicochemical perspective, aiming to provide a general overview of this critical process. Main issues related to NP toxicity and clearance from the body as a result of protein adsorption are covered, including the most promising strategies to control PC formation and, thereby, ensure the successful application of NPs in nanomedicine.

Nanoparticle-Induced Complement Activation: Implications for Cancer Nanomedicine

Nanoparticle-based anticancer medications were first approved for cancer treatment almost 2 decades ago. Patients benefit from these approaches because of the targeted-drug delivery and reduced toxicity, however, like other therapies, adverse reactions often limit their use. These reactions are linked to the interactions of nanoparticles with the immune system, including the activation of complement. This activation can cause well-characterized acute inflammatory reactions mediated by complement effectors. However, the long-term implications of chronic complement activation on the efficacy of drugs carried by nanoparticles remain obscured. The recent discovery of protumor roles of complement raises the possibility that nanoparticle-induced complement activation may actually reduce antitumor efficacy of drugs carried by nanoparticles. We discuss here the initial evidence supporting this notion. Better understanding of the complex interactions between nanoparticles, complement, and the tumor microenvironment appears to be critical for development of nanoparticle-based anticancer therapies that are safer and more efficacious.

One-year chronic toxicity evaluation of single dose intravenously administered silica nanoparticles in mice and their Ex vivo human hemocompatibility

Chronic toxicity evaluations of nanotechnology-based drugs are essential to support initiation of clinical trials. Ideally such evaluations should address the dosing strategy in human applications and provide sufficient information for long-term usage. Herein, we investigated one-year toxicity of non-surface modified silica nanoparticles (SNPs) with variations in size and porosity (Stöber SNPs 46 ± 4.9 and 432.0 ± 18.7 nm and mesoporous SNPs 466.0 ± 86.0 nm) upon single dose intravenous administration to female and male BALB/c mice (10 animal/sex/group) along with their human blood compatibility. Our evidence of clinical observation and blood parameters showed no significant changes in body weight, cell blood count, nor plasma biomarker indices. No significant changes were noted in post necropsy examination of internal organs and organ-to-body weight ratio. However, microscopic examination revealed significant amount of liver inflammation and aggregates of histocytes with neutrophils within the spleen suggesting an ongoing or resolving injury. The fast accumulation of these plain SNPs in the liver and spleen upon IV administration and the duration needed for their clearance caused these injuries. There were also subtle changes which were attributed to prior infarctions or resolved intravascular thrombosis and included calcifications in pulmonary vessels, focal cardiac fibrosis with calcifications, and focal renal injury. Most of the pathologic lesions were observed when large, non-porous SNPs were administered. Statistically significant chronic toxicity was not observed for the small non-porous particles and for the mesoporous particles. This one-year post-exposure evaluation indicate that female and male BALB/c mice need up to one year to recover from acute tissue toxic effects of silica nanoparticles upon single dose intravenous administration at their 10-day maximum tolerated dose. Further, ex vivo testing with human blood and plasma revealed no hemolysis or complement activation following incubation with these silica nanoparticles. These results can inform the potential utility of silica nanoparticles in biomedical applications such as controlled drug delivery where intravenous injection of the particles is intended.

Engineering at the nano-bio interface: harnessing the protein corona towards nanoparticle design and function

Unpredictable and uncontrollable protein adsorption on nanoparticles remains a considerable challenge to achieving effective application of nanotechnologies within biological environments. Nevertheless, engineered nanoparticles offer unprecedented functionality and control in probing and altering biological systems. In this review, we highlight recent advances in harnessing the "protein corona" formed on nanoparticles as a handle to tune functional properties of the protein-nanoparticle complex. Towards this end, we first review nanoparticle properties that influence protein adsorption and design strategies to facilitate selective corona formation, with the corresponding characterization techniques. We next focus on literature detailing corona-mediated functionalities, including stealth to avoid recognition and sequestration while in circulation, targeting of predetermined in vivo locations, and controlled activation once localized to the intended biological compartment. We conclude with a discussion of biocompatibility outcomes for these protein-nanoparticle complexes applied in vivo. While formation of the nanoparticle-corona complex may impede our control over its use for the projected nanobiotechnology application, it concurrently presents an opportunity to create improved protein-nanoparticle architectures by exploiting natural or guiding selective protein adsorption to the nanoparticle surface.

Development of a Sensitive Assay to Screen Nanoparticles in vitro for Complement Activation

Nanomedicines are often recognized by the innate immune system as a threat, leading to unwanted clearance due to complement activation. This adverse reaction not only alters the bioavailability of the therapeutic but can also cause cardiopulmonary complications and death in a portion of the population. There is a need for tools for assessing complement response in the early stage of development of nanomedicines. Currently, quantifying complement-mediated response in vitro is limited due to differences between in vitro and in vivo responses for the same precursors, differences in the complement systems in different species, and lack of highly sensitive tools for quantifying the changes. Hence, we have worked on developing complement assay conditions and sample preparation techniques that can be highly sensitive in assessing the complement-mediated response in vitro mimicking the in vivo activity. We are screening the impact of incubation time, nanoparticle dosage, anticoagulants, and species of the donor in both blood and blood components. We have validated the optimal assay conditions by replicating the impact of zeta potential seen in vivo on complement activation in vitro. As observed in our previous in vivo studies, where nanoparticles with neutral zeta-potential were able to suppress complement response, the change in the complement biomarker was least for the neutral nanoparticles as well through our developed guidelines. These assay conditions provide a vital tool for assessing the safety of intravenously administered nanomedicines.

Complement Inhibitors Block Complement C3 Opsonization and Improve Targeting Selectivity of Nanoparticles in Blood

Complement is one of the critical branches of innate immunity that determines the recognition of engineered nanoparticles by immune cells. Antibody-targeted iron oxide nanoparticles are a popular platform for magnetic separations, in vitro diagnostics, and molecular imaging. We used 60 nm cross-linked iron oxide nanoworms (CLIO NWs) modified with antibodies against Her2/neu and EpCAM, which are common markers of blood-borne cancer cells, to understand the role of complement in the selectivity of targeting of tumor cells in whole blood. CLIO NWs showed highly efficient targeting and magnetic isolation of tumor cells spiked in lepirudin-anticoagulated blood, but specificity was low due to high uptake by neutrophils, monocytes, and lymphocytes. Complement C3 opsonization in plasma was predominantly via the alternative pathway regardless of the presence of antibody, PEG, or fluorescent tag, but was higher for antibody-conjugated CLIO NWs. Addition of various soluble inhibitors of complement convertase (compstatin, soluble CD35, and soluble CD55) to whole human blood blocked up to 99% of the uptake of targeted CLIO NWs by leukocytes, which resulted in a more selective magnetic isolation of tumor cells. Using well-characterized nanomaterials, we demonstrate here that complement therapeutics can be used to improve targeting selectivity.

Complement activation by drug carriers and particulate pharmaceuticals: Principles, challenges and opportunities

Considering the multifaceted protective and homeostatic roles of the complement system, many consequences arise when drug carriers, and particulate pharmaceutical formulations clash with complement proteins, and trigger complement cascade. Complement activation may induce formulation destabilization, promote opsonization, and affect biological and therapeutic performance of pharmaceutical nano- and micro-particles. In some cases, complement activation is beneficial, where complement may play a role in prophylactic protection, whereas uncontrolled complement activation is deleterious, and contributes to disease progression. Accordingly, design initiatives with particulate medicines should consider complement activation properties of the end formulation within the context of administration route, dosing, systems biology, and therapeutic perspective. Here we examine current progress in mechanistic processes underlying complement activation by pre-clinical and clinical particles, identify opportunities and challenges ahead, and suggest future directions in nanomedicine-complement interface research.

Feraheme (Ferumoxytol) Is Recognized by Proinflammatory and Anti-inflammatory Macrophages via Scavenger Receptor Type AI/II

Feraheme (ferumoxytol), a negatively charged, carboxymethyl dextran-coated ultrasmall superparamagnetic iron oxide nanoparticle (USPIO, 30 nm, -16 mV), is clinically approved as an iron supplement and is used off-label for magnetic resonance imaging (MRI) of macrophage-rich lesions, but the mechanism of recognition is not known. We investigated mechanisms of uptake of Feraheme by various types of macrophages in vitro and in vivo. The uptake by mouse peritoneal macrophages was not inhibited in complement-deficient serum. In contrast, the uptake of larger and less charged SPIO nanoworms (60 nm, -5 mV; 120 nm, -5 mV, respectively) was completely inhibited in complement deficient serum, which could be attributed to more C3 molecules bound per nanoparticle than Feraheme. The uptake of Feraheme in vitro was blocked by scavenger receptor (SR) inhibitor polyinosinic acid (PIA) and by antibody against scavenger receptor type A I/II (SR-AI/II). Antibodies against other SRs including MARCO, CD14, SR-BI, and CD11b had no effect on Feraheme uptake. Intraperitoneally administered PIA inhibited the peritoneal macrophage uptake of Feraheme in vivo. Nonmacrophage cells transfected with SR-AI plasmid efficiently internalized Feraheme but not noncharged ultrasmall SPIO of the same size (26 nm, -6 mV), suggesting that the anionic carboxymethyl groups of Feraheme are responsible for the SR-AI recognition. The uptake by nondifferentiated bone marrow derived macrophages (BMDM) and by BMDM differentiated into M1 (proinflammatory) and M2 (anti-inflammatory) types was efficiently inhibited by PIA and anti-SR-AI/II antibody. Interestingly, all BMDM types expressed similar levels of SR-AI/II. In conclusion, Feraheme is efficiently recognized via SR-AI/II but not via complement by different macrophage types. The recognition by the common phagocytic receptor has implications for specificity of imaging of macrophage subtypes.

Immunotoxicity Considerations for Next Generation Cancer Nanomedicines

Although interest and funding in nanotechnology for oncological applications is thriving, translating these novel therapeutics through the earliest stages of preclinical assessment remains challenging. Upon intravenous administration, nanomaterials interact with constituents of the blood inducing a wide range of associated immunotoxic effects. The literature on the immunological interactions of nanomaterials is vast and complicated. A small change in a particular characteristic of a nanomaterial (e.g., size, shape, or charge) can have a significant effect on its immunological profile in vivo, and poor selection of specific assays for establishing these undesirable effects can overlook this issue until the latest stages of preclinical assessment. This work describes the current literature on unintentional immunological effects associated with promising cancer nanomaterials (liposomes, dendrimers, mesoporous silica, iron oxide, gold, and quantum dots) and puts focus on what is missing in current preclinical evaluations. Opportunities for avoiding or limiting immunotoxicity through efficient preclinical assessment are discussed, with an emphasis placed on current regulatory views and requirements. Careful consideration of these issues will ensure a more efficient preclinical assessment of cancer nanomedicines, enabling a smoother clinical translation with less failures in the future.

Towards a nanoparticle-based prophylactic for maternal autoantibody-related autism

Recently, the causative agents of Maternal Autoantibody-Related (MAR) autism, pathological autoantibodies and their epitopic targets (e.g. lactate dehydrogenase B [LDH B] peptide), have been identified. Herein, we report on the development of Systems for Nanoparticle-based Autoantibody Reception and Entrapment (SNAREs), which we hypothesized could scavenge disease-propagating MAR autoantibodies from the maternal blood. To demonstrate this functionality, we synthesized 15 nm dextran iron oxide nanoparticles surface-modified with citric acid, methoxy PEG(10 kDa) amine, and LDH B peptide (33.8 μg peptide/cm2). In vitro, we demonstrated significantly lower macrophage uptake for SNAREs compared to control NPs. The hallmark result of this study was the efficacy of the SNAREs to remove 90% of LDH B autoantibody from patient-derived serum. Further, in vitro cytotoxicity testing and a maximal tolerated dose study in mice demonstrated the safety of the SNARE formulation. This work establishes the feasibility of SNAREs as the first-ever prophylactic against MAR autism.

The Interplay Between Blood Proteins, Complement, and Macrophages on Nanomedicine Performance and Responses

In the blood, depending on their physicochemical characteristics, nanoparticles attract a wide range of plasma biomolecules. The majority of blood biomolecules bind nonspecifically to nanoparticles. On the other hand, biomolecules such as pattern-recognition complement-sensing proteins may recognize some structural determinants of the pristine surface, causing complement activation. Adsorption of nonspecific blood proteins could also recruit natural antibodies and initiate complement activation, and this seems to be a global process with many preclinical and clinical nanomedicines. We discuss these issues, since complement activation has ramifications in nanomedicine stability and pharmacokinetics, as well as in inflammation and disease progression. Some studies have also predicted a role for complement systems in infusion-related reactions, whereas others show a direct role for macrophages and other immune cells independent of complement activation. We comment on these discrepancies and suggest directions for exploring the underlying mechanisms.

Overview of the blood compatibility of nanomedicines: A trend analysis of in vitro and in vivo studies

As nanomedicines have the potential to address many currently unmet medical needs, the early identification of regulatory requirements that could hamper a smooth translation of nanomedicines from the laboratory environment to clinical applications is of utmost importance. The blood system is especially relevant as many nanomedicinal products that are currently under development are designed for intravenous administration and cells of the blood system will be among the first biological systems exposed to the injected nanomedicine. This review collects and summarizes the current knowledge related to the blood compatibility of nanomedicines and nanomaterials with a potential use in biomedical applications. Different types of nanomedicines were analyzed for their toxicity to the blood system, and the role of their physicochemical properties was further elucidated. Trends were identified related to: (a) the nature of the most frequently occurring blood incompatibilities such as thrombogenicity and complement activation, (b) the contribution of physicochemical properties to these blood incompatibilities, and (c) the similarities between data retrieved from in vivo and in vitro studies. Finally, we provide an overview of available standards that allow evaluating the compatibility of a material with the blood system. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials Therapeutic Approaches and Drug Discovery > Emerging Technologies Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.

Hemocompatibility of amyloid and/or brain targeted liposomes

Targeted liposomes with different combinations of five ligands (for brain/amyloid targeting) were evaluated for hemocompatibility. Results reveal that all liposomes studied, caused minimum hemolysis; targeted liposomes slightly reduced blood coagulation time, but not significantly more than control liposomes; and compliment factors SC5b9 and iC3b increased when compared with the buffer, by most targeted liposomes. However, the specific amounts of both factors were similar with those induced by control liposomes. Thus, the targeted liposomes are unanticipated to cause hypersensitivity problems. Good correlations between vesicle size and produced factor amounts were observed. In conclusion, the current targeted liposomes are not expected to cause serious blood toxicity, if used in vivo.

Immunoglobulin deposition on biomolecule corona determines complement opsonization efficiency of preclinical and clinical nanoparticles

Deposition of complement factors (opsonization) on nanoparticles may promote clearance from the blood by macrophages and trigger proinflammatory responses, but the mechanisms regulating the efficiency of complement activation are poorly understood. We previously demonstrated that opsonization of superparamagnetic iron oxide (SPIO) nanoworms with the third complement protein (C3) was dependent on the biomolecule corona of the nanoparticles. Here we show that natural antibodies play a critical role in C3 opsonization of SPIO nanoworms and a range of clinically approved nanopharmaceuticals. The dependency of C3 opsonization on immunoglobulin binding is almost universal and is observed regardless of the complement activation pathway. Only a few surface-bound immunoglobulin molecules are needed to trigger complement activation and opsonization. Although the total amount of plasma proteins adsorbed on nanoparticles does not determine C3 deposition efficiency, the biomolecule corona per se enhances immunoglobulin binding to all nanoparticle types. We therefore show that natural antibodies represent a link between biomolecule corona and C3 opsonization, and may determine individual complement responses to nanomedicines.

Accelerated Blood Clearance of Antibodies by Nanosized Click Antidotes

Long blood half-life is one of the advantages of antibodies over small molecule drugs. At the same time, prolonged half-life is a problem for imaging applications or in the case of antibody-induced toxicities. There is a substantial need for antidotes that can quickly clear antibodies from systemic circulation and peripheral tissues. Engineered nanoparticles exhibit intrinsic affinity for clearance organs (mainly liver and spleen). trans-Cyclooctene (TCO) and methyltetrazine (MTZ) are versatile copper-free click chemistry components that are extensively being used for in vivo bioorthogonal couplings. To test the ability of nanoparticles to eliminate antibodies, we prepared a set of click-modified, clinically relevant antidotes based on several classes of drug carriers: phospholipid-PEG micelles, bovine serum albumin (BSA), and cross-linked dextran iron oxide (CLIO) nanoparticles. Mice were injected with IRDye 800CW-labeled, click-modified IgG followed by a click-modified antidote or PBS (control), and the levels of the IgG were monitored up to 72 h postinjection. Long-circulating lipid micelles produced a spike in IgG levels at 1 h, decreased IgG levels at 24 h, and did not decrease the area under the curve (AUC) and IgG accumulation in main organs. Long-circulating BSA decreased IgG levels at 1 and 24 h, decreased the AUC, but did not significantly decrease organ accumulation. Long-circulating CLIO nanoworms increased IgG levels at 1 h, decreased IgG levels at 24 h, did not decrease the AUC, and did not decrease the organ accumulation. On the other hand, short-circulating CLIO nanoparticles decreased IgG levels at 1 and 24 h, significantly decreasing the AUC and accumulation in the main organs. Multiple doses of CLIO and BSA were not able to completely eliminate the antibody from blood, despite the click reactivity of the residual IgG, likely due to exchange of IgG between blood and tissue compartments. Pharmacokinetic modeling suggests that short antidote half-life and fast click reaction rate should result in higher IgG depletion efficiency. Short-circulating click-modified nanocarriers are the most effective antidotes for elimination of antibodies from blood. This study sets a stage for future development of antidotes based on nanomedicine.

Synthesis and characterization of biofunctional quaternized xylan-Fe2O3 core/shell nanocomposites and modification with polylysine and folic acid

The aims of this study are to prepare quaternized xylan-Fe₂O₃ (QX-Fe₂O₃) core/shell nanocomposites and explore their potential application in the biomedical fields. γ-Fe₂O₃ nanoparticles synthesized by a facile solvothermal process are coated with QX via reverse microemulsion method and further modified by polylysine (PLL) and folic acid (FA) to prepare PLL-QX-Fe₂O₃ and FA-QX-Fe₂O₃ nanoparticles. An obvious strong absorption of γ-Fe₂O₃ at 580 cm^-1 in the spectra of QX-Fe₂O₃ is observed, the Fe element content of QX-Fe₂O₃ is 30-75 μg/mL and the saturation magnetization of QX-Fe₂O₃ nanoparticles is 1.49 emu/g. The γ-Fe₂O₃ and QX-Fe₂O₃ nanoparticles are of regular sphericity with diameter of 50-100 nm and 60-150 nm, respectively. The highest zeta potential of QX-Fe₂O₃ nanoparticles is -41 mV, and the PLL-QX-Fe₂O₃ nanoparticles have a positive potential with a maximum value of 45.2 mV. In addition, FA-QX-Fe₂O₃ showed excellent performance in T₂-weighted Magnetic Resonance (MR) imaging with an r₂ value of 190 mM^-1S^-1. Each nanocomposite has its own inherent properties, which contributes to its versatile utilization and application potential.

Properdin: A multifaceted molecule involved in inflammation and diseases

Properdin, the widely known positive regulator of the alternative pathway (AP), has undergone significant investigation over the last decade to define its function in inflammation and disease, including its role in arthritis, asthma, and kidney and cardiovascular diseases. Properdin is a glycoprotein found in plasma that is mainly produced by leukocytes and can positively regulate AP activity by stabilizing C3 and C5 convertases and initiating the AP. Promotion of complement activity by properdin results in changes in the cellular microenvironment that contribute to innate and adaptive immune responses, including pro-inflammatory cytokine production, immune cell infiltration, antigen presenting cell maturation, and tissue damage. The use of properdin-deficient mouse models and neutralizing antibodies has contributed to the understanding of the mechanisms by which properdin contributes to promoting or preventing disease pathology. This review mainly focusses on the multifaceted roles of properdin in inflammation and diseases, and how understanding these roles is contributing to the development of new disease therapies.

Unintended effects of drug carriers: Big issues of small particles

Humoral and cellular host defense mechanisms including diverse phagocytes, leukocytes, and immune cells have evolved over millions of years to protect the body from microbes and other external and internal threats. These policing forces recognize engineered sub-micron drug delivery systems (DDS) as such a threat, and react accordingly. This leads to impediment of the therapeutic action, extensively studied and discussed in the literature. Here, we focus on side effects of DDS interactions with host defenses. We argue that for nanomedicine to reach its clinical potential, the field must redouble its efforts in understanding the interaction between drug delivery systems and the host defenses, so that we can engineer safer interventions with the greatest potential for clinical success.

Dextran-coated superparamagnetic iron oxide nanoparticles for magnetic resonance imaging: evaluation of size-dependent imaging properties, storage stability and safety

BACKGROUND

Rising criticism of currently available contrast agents for magnetic resonance imaging, either due to their side effects or limited possibilities in terms of functional imaging, evoked the need for safer and more versatile agents. We previously demonstrated the suitability of novel dextran-coated superparamagnetic iron oxide nanoparticles (SPIONDex) for biomedical applications in terms of safety and biocompatibility.

METHODS

In the present study, we investigated the size-dependent cross-linking process of these particles as well as the size dependency of their imaging properties. For the latter purpose, we adopted a simple and easy-to-perform experiment to estimate the relaxivity of the particles. Furthermore, we performed an extensive analysis of the particles' storage stability under different temperature conditions, showing their superb stability and the lack of any signs of agglomeration or sedimentation during a 12 week period.

RESULTS

Independent of their size, SPIONDex displayed no irritation potential in a chick chorioallantoic membrane assay. Cell uptake studies of ultra-small (30 nm) SPIONDex confirmed their internalization by macrophages, but not by non-phagocytic cells. Additionally, complement activation-related pseudoallergy (CARPA) experiments in pigs treated with ultra-small SPIONDex indicated the absence of hypersensitivity reactions.

CONCLUSION

These results emphasize the exceptional safety of SPIONDex, setting them apart from the existing SPION-based contrast agents and making them a very promising candidate for further clinical development.

Variability of Complement Response toward Preclinical and Clinical Nanocarriers in the General Population

Opsonization (coating) of nanoparticles with complement C3 component is an important mechanism that triggers immune clearance and downstream anaphylactic and proinflammatory responses. The variability of complement C3 binding to nanoparticles in the general population has not been studied. We examined complement C3 binding to dextran superparamagnetic iron oxide nanoparticles (superparamagnetic iron oxide nanoworms, SPIO NWs, 58 and 110 nm) and clinically approved nanoparticles (carboxymethyl dextran iron oxide ferumoxytol (Feraheme, 28 nm), highly PEGylated liposomal doxorubicin (LipoDox, 88 nm), and minimally PEGylated liposomal irinotecan (Onivyde, 120 nm)) in sera from healthy human individuals. SPIO NWs had the highest variation in C3 binding (n = 47) between subjects, with a 15-30 fold range in levels of C3. LipoDox (n = 12) and Feraheme (n = 18) had the lowest levels of variation between subjects (an approximately 1.5-fold range), whereas Onivyde (n = 18) had intermediate between-subject variation (2-fold range). There was no statistical difference between males and females and no correlation with age. There was a significant correlation in complement response between small and large SPIO NWs, which are similar structurally and chemically, but the correlations between SPIO NWs and other types of nanoparticles, and between LipoDox and Onivyde, were not significant. The calculated average number of C3 molecules bound per nanoparticle correlated with the hydrodynamic diameter but was decreased in LipoDox, likely due to the PEG coating. The conclusions of this study are (1) all nanoparticles show variability of C3 opsonization in the general population; (2) an individual's response toward one nanoparticle cannot be reliably predicted based on another nanoparticle; and (3) the average number of C3 molecules per nanoparticle depends on size and surface coating. These results provide new strategies to improve nanomedicine safety.

Iron oxide nanoparticles induce cytokine secretion in a complement-dependent manner in a human whole blood model

Iron oxide nanoparticles (IONPs) are promising nanomaterials for biomedical applications. However, their inflammatory potential has not been fully established. Here, we used a lepirudin anti-coagulated human whole blood model to evaluate the potential of 10 nm IONPs to activate the complement system and induce cytokine production. Reactive oxygen species and cell death were also assessed. The IONPs activated complement, as measured by C3a, C5a and sC5b-9, and induced the production of pro-inflammatory cytokines in a particle-dose dependent manner, with the strongest response at 10 µg/mL IONPs. Complement inhibitors at C3 (compstatin analog Cp40) and C5 (eculizumab) levels completely inhibited complement activation and secretion of inflammatory mediators induced by the IONPs. Additionally, blockade of complement receptors C3aR and C5aR1 significantly reduced the levels of various cytokines, indicating that the particle-induced secretion of inflammatory mediators is mainly C5a and C3a mediated. The IONPs did not induce cell death or reactive oxygen species, which further suggests that complement activation alone was responsible for most of the particle-induced cytokines. These data suggest that the lepirudin anti-coagulated human whole blood model is a valuable ex vivo system to study the inflammatory potential of IONPs. We conclude that IONPs induce complement-mediated cytokine secretion in human whole blood.

In Vitro and In Vivo Differences in Murine Third Complement Component (C3) Opsonization and Macrophage/Leukocyte Responses to Antibody-Functionalized Iron Oxide Nanoworms

Balancing surface functionalization and low immune recognition of nanomedicines is a major challenge. Opsonization with the third component of the complement protein (C3) plays a major role in immune cell recognition of nanomedicines. We used dextran-coated superparamagnetic iron oxide nanoworms (SPIO NWs) to study the effect of surface functionalization on C3 opsonization in mouse serum and subsequent macrophage/leukocyte recognition in vitro as well as on intravenous injection into mice. Previously, we found that in mouse serum, SPIO NWs became opsonized with C3 via complement lectin pathway. Crosslinking the dextran shell with epichlorohydrin significantly decreased C3 opsonization and uptake by mouse peritoneal macrophages. Crosslinked nanoworms (NWs) further functionalized with polyethylene glycol (PEG) or with PEG-antibody (Ab) (~160 IgG molecules/particle) did not show an increase in C3 opsonization and peritoneal macrophage uptake in vitro. Following tail vein injection into mice, plain crosslinked NWs and PEGylated crosslinked NWs showed very low C3 opsonization and mouse leukocyte uptake. However, Ab-decorated crosslinked NWs showed significant C3 opsonization and high level of complement-dependent uptake by leukocytes in mice. Decreasing the number of conjugated Abs to 46 IgG molecules/particle significantly reduced C3 opsonization and leukocyte uptake. Using fresh mouse lepirudin plasma rather than serum showed better correlation with C3 opsonization in vivo. The reason for this difference could be related to the known instability of complement classical pathway in mouse sera. Our data illustrate that fine-tuning in nanoparticle surface functionalization with Abs is required to avoid excessive complement activation and complement-mediated immune uptake in mice, and raise issues with in vitro immunological assays of nanomedicines intended to mimic in vivo conditions.