Hybrid proteins of Cobra Venom Factor and cobra C3: tools to identify functionally important regions in Cobra Venom Factor

Combined analysis of single-cell sequencing and bulk transcriptome sequencing reveals new mechanisms for non-healing diabetic foot ulcers

Diabetic foot ulcers (DFUs) pose a significant challenge in diabetes care. Yet, a comprehensive understanding of the underlying biological disparities between healing and non-healing DFUs remains elusive. We conducted bioinformatics analysis of publicly available transcriptome sequencing data in an attempt to elucidate these differences. Our analysis encompassed differential analysis to unveil shifts in cell composition and gene expression profiles between non-healing and healing DFUs. Cell communication alterations were explored employing the Cellchat R package. Pseudotime analysis and cytoTRACE allowed us to dissect the heterogeneity within fibroblast subpopulations. Our findings unveiled disruptions in various cell types, localized low-grade inflammation, compromised systemic antigen processing and presentation, and extensive extracellular matrix signaling disarray in non-healing DFU patients. Some of these anomalies partially reverted in healing DFUs, particularly within the abnormal ECM-receptor signaling pathway. Furthermore, we distinguished distinct fibroblast subpopulations in non-healing and healing DFUs, each with unique biological functions. Healing-associated fibroblasts exhibited heightened extracellular matrix (ECM) remodeling and a robust wound healing response, while non-healing-associated fibroblasts showed signs of cellular senescence and complement activation, among other characteristics. This analysis offers profound insights into the wound healing microenvironment, identifies pivotal cell types for DFU healing promotion, and reveals potential therapeutic targets for DFU management.

Identification of intermolecular bonds between human factor B and Cobra Venom Factor important for C3 convertase stability

Cobra venom factor (CVF) is the complement-activating protein in cobra venom. CVF is a structural and functional analog of complement component C3. CVF, like C3b, forms a convertase with factor B. This bimolecular complex CVF, Bb is an enzyme that cleaves C3 and C5. However, CVF, Bb exhibits significantly different functional properties from C3b,Bb. Whereas both, CVF, Bb and C3b, Bb exhibit spontaneous decay-dissociation into the respective subunits, thereby eliminating the enzymatic activity, the CVF, Bb convertase is physico-chemically far more stable, decaying with a half-life that is more than two orders of magnitude slower than that of C3b,Bb. In addition, CVF, Bb is completely resistant to inactivation by Factors H and I. These two properties of CVF, Bb allow continuous activation of C3 and C5, and complement depletion in serum. In order to understand the structural basis for the physico-chemical stability of CVF,Bb, we have created recombinant hybrid proteins of CVF and human C3, based on structural differences between CVF and human C3b in the C-terminal C345C domain. Here we describe three human C3/CVF hybrid proteins which differ in only one, two, or five amino acid residues from earlier described hybrid proteins. In all three cases, the hybrid proteins containing CVF residues form more stable convertases, and exhibit stronger complement-depletion activity than hybrid proteins with human C3 residues. Three bonds between CVF residues and Factor Bb residues could be identified by crystallographic modeling that contribute to the greater stability of the convertases.

Complement C3 participates in the function and mechanism of traumatic brain injury at simulated high altitude

BACKGROUND

Traumatic brain injury (TBI) leads to severe mortality and disability, in which secondary injury induced by complement activation plays an important role. TBI tends to be associated with more severe cerebral edema and worse neurological functional recovery if it occurs in high-altitude areas than in low-altitude areas. However, the underlying mechanism of this difference is unknown. Thus, we used cobra venom factor (CVF) to deplete complement C3 in simulated high-altitude areas to explore whether the differences in outcome at different altitudes are related to secondary injury caused by complement C3.

METHODS

The weight-drop model was adopted to induce TBI in rats. Rats were randomly divided into the following groups: sham + saline (sham), high altitude + TBI + saline (HAT), high altitude + TBI + CVF (H-CVF), low altitude + TBI + saline (LAT), and low altitude + TBI + CVF (L-CVF). Brain contusion and edema volumes, brain water content, myelin basic protein (MBP) expression, tumor necrosis factor alpha (TNF-a) expression, interleukin 1 beta (IL1B) expression, mortality rate, neurological function, and complement component 3 (C3) mRNA expression were measured by techniques such as Evans blue fluorescence, Perls staining, TUNEL staining, ELISA, immunohistochemistry and Western blotting to evaluate correlations between complement activation and secondary injury.

RESULTS

The activation of complement after TBI was significantly higher at high altitude than at low altitude. High-altitude TBI resulted in a leakier blood-brain barrier, more severe cerebral edema and higher mortality than low-altitude TBI did. In addition, high-altitude TBI tended to be associated with more MBP degradation, ferric iron deposition, neuronal apoptosis, and inflammatory factor deposition than low-altitude TBI. All of these effects of TBI were partially reversed by inhibiting complement activation using CVF.

CONCLUSION

Our study provided evidence that TBI at high altitude leads to severe edema and high mortality and disability rates. Complement C3 activation is one of the important factors contributing to secondary brain injury.

Absence of a neutralizing antibody response to humanized cobra venom factor in mice

Cobra venom factor (CVF) is the complement-activating protein in cobra venom. Humanized CVF (hCVF) is a human C3 derivative where the C-terminal 168 amino acid residues were replaced with the homologous sequence from CVF. hCVF has been shown in multiple models of disease with complement pathology to be a promising therapeutic agent, with no observed adverse effects. Here we describe the antibody response to hCVF in two different strains of mice. hCVF was able to repeatedly decomplement the mice after four injections in weekly intervals, demonstrating the absence of a neutralizing antibody response. In contrast, natural CVF caused decomplementation in all mice only after the first administration. After two additional administrations of natural CVF, decomplementation was inconsistent and varied tremendously from mouse to mouse. After the fourth administration, natural CVF was essentially unable to deplete complement, consistent with the known generation of a neutralizing antibody response. We also analyzed the IgG antibody response to hCVF. There was great variation, with approximately one quarter of the mice exhibiting non-detectable levels of anti-hCVF IgG, and another quarter very low levels. The levels of anti-hCVF IgG did not correlate with the levels of remaining C3. The anti-hCVF antibodies cross-reacted with natural CVF, recombinant CVF, and human C3. Whereas overall the level of anti-hCVF IgG cross-reacting with human C3 was lower compared to rCVF or nCVF, mice with higher levels of anti-hCVF IgG exhibited higher binding to CVF and human C3, excluding the possibility that higher antibody levels reflect preferential immunogenicity of CVF-specific or human C3-specific epitopes.

Complement depletion with humanised cobra venom factor: Efficacy in preclinical models of vascular diseases

The complement system is an intrinsic part of the immune system and has important functions in both innate and adaptive immunity. On the other hand, inadvertent or misdirected complement activation is also involved in the pathogenesis of many diseases, contributing solely or significantly to tissue injury and disease development. Multiple approaches to develop pharmacological agents to inhibit complement are currently being pursued. We have developed a conceptually different approach of not inhibiting but depleting complement, based on the complement-depleting activities of cobra venom factor (CVF), a non-toxic cobra venom component with structural and functional homology to complement component C3. We developed a humanised version of CVF by creating human complement component C3 derivatives with complement-depleting activities of CVF (humanised CVF) as a promising therapeutic agent for diseases with complement pathogenesis. Here we review the beneficial therapeutic effect of humanised CVF in several murine models of vascular diseases such as reperfusion injury.

Complement activation and inhibition in wound healing

Complement activation is needed to restore tissue injury; however, inappropriate activation of complement, as seen in chronic wounds can cause cell death and enhance inflammation, thus contributing to further injury and impaired wound healing. Therefore, attenuation of complement activation by specific inhibitors is considered as an innovative wound care strategy. Currently, the effects of several complement inhibitors, for example, the C3 inhibitor compstatin and several C1 and C5 inhibitors, are under investigation in patients with complement-mediated diseases. Although (pre)clinical research into the effects of these complement inhibitors on wound healing is limited, available data indicate that reduction of complement activation can improve wound healing. Moreover, medicine may take advantage of safe and effective agents that are produced by various microorganisms, symbionts, for example, medicinal maggots, and plants to attenuate complement activation. To conclude, for the development of new wound care strategies, (pre)clinical studies into the roles of complement and the effects of application of complement inhibitors in wound healing are required.