Evaluating the immunogenicity of heparin and heparin derivatives by measuring their binding to platelet factor 4 using biolayer interferometry

Investigation into the binding domains of platelet factor 4 unlocks new avenues for the design and synthesis of selective sulfated pseudo-tetrasaccharide aminoglycoside ligands

Platelet factor 4 (PF4) is a natural chemokine that binds to negatively charged glycosaminoglycans (GAGs), including the anticoagulant heparin. The formation of the PF4-heparin complex elicits an immune response that results in platelet activation, leading to serious thrombotic complications. This study explores the structure-activity relationships (SAR) of sulfated pseudo-tetrasaccharide aminoglycoside ligands. The binding interactions of these synthetically designed compounds with heparanase (HPSE) and PF4 were systematically elucidated. Through computational design, a library of sulfated aminoglycoside ligands was synthesized in 10-13 steps from readily available paromomycin and neomycin. The SAR studies revealed that hydroxyl-capped ligands interacted with the fondaparinux-binding domain of PF4, while hydrophobic-capped ligands bound to the heparin-binding domain. Notably, steric hindrance imposed by hydrophobic groups impedes the binding of the ligands to PF4's shallow binding site. In contrast, these hydrophobic-capped ligands demonstrated a strong binding affinity for HPSE. The most selective ligands reduced the viability of HPSE-overexpressing cancer cells, highlighting their potential efficacy in modulating the enzymatic activity of HPSE. This SAR study provides a foundational framework for the design of sulfated aminoglycoside-based therapeutics with minimized adverse effects associated with PF4.

Emodin mitigates rheumatoid arthritis through direct binding to TNF-α

Emodin has shown certain anti-rheumatoid arthritis (RA) activity in preliminary studies. However, the precise mechanisms of emodin's anti-RA effects, particularly its direct targets, remain unclear. This study aimed to evaluate the anti-RA activity of emodin and elucidate its potential mechanisms, with a specific focus on identifying its molecular targets. Employing a collagen-induced arthritis (CIA) rat model, along with transcriptomic analysis, thermal proteome profiling (TPP) and TNF-α-induced L929 cell model, the anti-RA activity of emodin was confirmed, identifying TNF-α as a potential target. Techniques such as drug affinity responsive target stability (DARTS), cellular thermal shift assay (CETSA), Affinity ultrafiltration-liquid chromatography/mass spectrometry (AUF-LC/MS), surface plasmon resonance (SPR) and bio-layer interferometry (BLI) validated the direct binding of emodin to TNF-α. Molecular dynamics simulation, ELISA and BLI further revealed that emodin stabilizes the asymmetric trimeric structure of TNF-α, disrupting the TNF-α-TNFR1 interaction. In vitro assays, including luciferase reporter gene assay and TNF-α-induced MH7A cell model, demonstrated that this disruption inhibits TNF-α-induced NF-κB activation, leading to the downregulation of inflammatory mediators such as IL-6, IL-1β, and COX2. In conclusion, emodin directly targets TNF-α, stabilizing its structure and blocking TNF-α-TNFR1 interaction, which subsequently suppresses downstream NF-κB pathway activation and contributes to its potent anti-RA properties.

Anti-Platelet factor 4 immunothrombosis-not just heparin and vaccine triggers

Derailments at the tightly regulated interface of blood coagulation and innate inflammatory immune responses can lead to pathologic immunothrombosis. A special subset of immunothrombosis is caused by antibodies against platelet-factor 4 (PF4). Anti-PF4 antibodies triggered by heparin treatment in heparin-induced thrombocytopenia (HIT) are known for more than 50 years. Interest in anti-PF4 disorders rekindled when first cases of vaccine-induced immune thrombocytopenia and thrombosis (VITT) occurred during the worldwide COVID-19 vaccination campaign. During this time new diagnostic procedures were established to identify affected patients and to differentiate between different kinds of anti-PF4 antibodies. This review article gives an overview about the current knowledge of HIT and VITT with concepts of the underlying pathogenesis. In addition to heparin and vaccination as known triggers for HIT and VITT, concepts for other clinical cases with anti-PF4 antibodies are described in more detail. Anti-PF4 antibodies in atypical HIT-like syndromes could be triggered by presentation of various polyanions, eg, in settings of orthopedic surgery or bacterial infections. Anti-PF4 antibodies in acute VITT-like disorders can occur after viral infections. Chronic VITT-like anti-PF4 antibodies causing recurrent thrombosis and thrombocytopenia are often linked to monoclonal gammopathies. For all disorders with anti-PF4 antibodies, timely identification in patients with thrombocytopenia with or without thrombosis is crucial for successful therapy.

Low molecular weight heparin promotes the PPAR pathway by protecting the glycocalyx of cells to delay the progression of diabetic nephropathy

Diabetic nephropathy (DN) is one of the most important comorbidities for diabetic patients, which is the main factor leading to end-stage renal disease. Heparin analogs can delay the progression of DN, but the mechanism is not fully understood. In this study, we found that low molecular weight heparin therapy significantly upregulated some downstream proteins of the peroxisome proliferator-activated receptor (PPAR) signaling pathway by label-free quantification of the mouse kidney proteome. Through cell model verification, low molecular weight heparin can protect the heparan sulfate of renal tubular epithelial cells from being degraded by heparanase that is highly expressed in a high-glucose environment, enhance the endocytic recruitment of fatty acid-binding protein 1, a coactivator of the PPAR pathway, and then regulate the activation level of intracellular PPAR. In addition, we have elucidated for the first time the molecular mechanism of heparan sulfate and fatty acid-binding protein 1 interaction. These findings provide new insights into understanding the role of heparin in the pathogenesis of DN and developing corresponding treatments.

Inhibition of catechol-O-methyltransferase (COMT) by heparin oligosaccharides with specific structures

COMT inhibitors are commonly used to improve the effectiveness of levodopa in treating Parkinson's disease by inhibiting its conversion to 3-O-methyldopa. Because of the serious side effect of nitrocatechol COMT inhibitors, it is necessary to develop non-nitrocatechol COMT inhibitors with a higher safety profile. Heparin has been observed to bind to COMT. However, the exact functional significance of this interaction is not fully understood. In this study, the contribution of different substitution of heparin to its binding with COMT was investigated. In vitro and in vivo, heparin oligosaccharides can bind to COMT and inhibit its activity. Furthermore, we enriched the functional heparin oligosaccharides that bind to COMT and identified the sequence UA2S-GlcN(S/Ac)6(S/H)-UA2S-GlcNS6(S/H)-UA2(S/H)-GlcNS6S as the characteristic structural domain of these functional oligosaccharides. This study has elucidated the relationship between the structure of heparin oligosaccharides and their activity against COMT, providing valuable insights for the development of non-nitrocatechol COMT inhibitors with improved safety and efficacy.

Sweet but Challenging: Tackling the Complexity of GAGs with Engineered Tailor-Made Biomaterials

Glycosaminoglycans (GAGs) play a crucial role in tissue homeostasis by regulating the activity and diffusion of bioactive molecules. Incorporating GAGs into biomaterials has emerged as a widely adopted strategy in medical applications, owing to their biocompatibility and ability to control the release of bioactive molecules. Nevertheless, immobilized GAGs on biomaterials can elicit distinct cellular responses compared to their soluble forms, underscoring the need to understand the interactions between GAG and bioactive molecules within engineered functional biomaterials. By controlling critical parameters such as GAG type, density, and sulfation, it becomes possible to precisely delineate GAG functions within a biomaterial context and to better mimic specific tissue properties, enabling tailored design of GAG-based biomaterials for specific medical applications. However, this requires access to pure and well-characterized GAG compounds, which remains challenging. This review focuses on different strategies for producing well-defined GAGs and explores high-throughput approaches employed to investigate GAG-growth factor interactions and to quantify cellular responses on GAG-based biomaterials. These automated methods hold considerable promise for improving the understanding of the diverse functions of GAGs. In perspective, the scientific community is encouraged to adopt a rational approach in designing GAG-based biomaterials, taking into account the in vivo properties of the targeted tissue for medical applications.