Sulfated Dendritic Polyglycerol Is a Potent Complement Inhibitor

Abstract

The complement system is a powerful mechanism of the innate immune defense system. Dysregulation may contribute to several diseases. Heparin is a known regulator of the complement system, but its application is limited due to its anticoagulative activity. A promising alternative is the synthetic analogue dendritic polyglycerol sulfate (dPGS). Although dPGS-mediated inhibition of the classical and alternative pathway has been roughly described previously, here we analyzed the effects of dPGS regarding the three pathways at different levels of the proteolytic cascades for the first time. Regarding the final outcome (membrane attack complex formation), IC50 values for dPGS varied between the alternative (900 nM), the classical (300 nM), and the lectin pathway (60 nM). In a backward approach, processing of proteins C5 and C3 via the respective convertase was analyzed by ELISA to narrow down dPGS targets. A dose-dependent reduction of C5a and C3a levels was detected. Further, the analysis via surface plasmon resonance revealed novel dPGS binding proteins; the pro-inflammatory anaphylatoxins C3a and C5a and the classical pathway activator C1q showed down to nanomolar binding affinities. The fully synthetic multivalent polymer dPGS seems to be a promising candidate for the further development to counteract excessive complement activation in disease.

Understanding the Interaction of Polyelectrolyte Architectures with Proteins and Biosystems

“…In the meantime, several inflammation and tumor‐relevant proteins were identified as nanomolar binders for dPGS, such as interleukin‐1 (IL‐1), L‐selectin, P‐selectin, interleukin‐6 (IL‐6), [198] lectin‐type oxidized low‐density lipoprotein receptor 1 (LOX‐1), [199] and the complement factors C1q and C5a [200] . The binding of dPGS is rather unspecific and does not necessarily depend on a unique protein structure.…”

“…identified that dPGS targets the three different pathways of the complement cascade and that charge–charge interaction plays an important role to balance the activation (Figure 8). [200] It was shown that dPGS binding to the complement factors C3 and C5 inhibits further processing and subsequent release of the anaphylatoxins C3a and C5a. In addition, charge‐dependent sequestration limits the anaphylatoxin function.…”

“…In addition, charge‐dependent sequestration limits the anaphylatoxin function. Highly charged polyelectrolytes such as heparin and heparan sulfate were shown to act similarly, [204] but by far not as effective as the synthetic polymer dPGS that binds the anaphylatoxin C3a with low micromolar affinity and C5a with nanomolar affinity [200] . Thus, dPGS may be a promising candidate for a drug that counteracts an overshooting complement activation in sepsis and other diseases such as rheumatoid arthritis [205–207] …”

“… Complement pathway: dPGS interferes with the three pathways of complement activation and reduces formation of the membrane attack complex (MAC), which is a pore that is inserted into the cytoplasmic membrane and thereby leads to cell death. Reduced activity of the C3 and C5 convertase results in IC 50 values of 60 n m (lectin pathway), 300 n m (classical pathway), and 900 n m (alternative pathway) [200] …”

Wechselwirkung von Polyelektrolyt‐Architekturen mit Proteinen und Biosystemen

“…Inzwischen konnten mehrere entzündungs‐ und tumorrelevante Proteine als nanomolare Interaktionspartner für dPGS identifiziert werden, z. B. Interleukin‐1 (IL‐1), L‐Selektin, P‐Selektin, Interleukin‐6 (IL‐6), [198] der lektinartige oxidierte Low‐Density‐Lipoprotein‐Rezeptor 1 (LOX‐1) [199] und die Komplementfaktoren C1q und C5a [200] . Die Bindungseigenschaften der dPGS‐Wechselwirkung sind eher unspezifisch und hängen nicht unbedingt von einer eindeutigen Proteinstruktur ab.…”