Low-molecular weight inhibitors of the alternative complement pathway

Emerging Oral Pharmaceuticals for Dry Age-Related Macular Degeneration: Mechanism of Action, Current Clinical Status, and Future Directions

Dry age-related macular degeneration (AMD) has been historically managed with lifestyle modifications, monitoring for conversion to wet AMD, and vitamins. Recently there has been a flurry of research focused on discovering new targets to prevent worsening of dry AMD. In 2023, the US Food and Drug Administration approved the first two intravitreal complement inhibitors to slow the rate of geographic atrophy progression. However, serial intravitreal injections for a chronic progressive disease are burdensome for patients and have procedural risks. Therefore, there is significant research to discover novel oral medications to manage dry AMD. Several oral medications are currently in phase 2 and 3 clinical trials for dry AMD, whereas others have had recent readouts on their clinical trials and efficacy. The purpose of this review is to describe the therapeutic pathways currently being investigated and to provide an update on the clinical status of novel oral medications for the management of dry AMD. [Ophthalmic Surg Lasers Imaging Retina 2024;55:XX-XX.].

mRNA-LNP COVID-19 Vaccine Lipids Induce Complement Activation and Production of Proinflammatory Cytokines: Mechanisms, Effects of Complement Inhibitors, and Relevance to Adverse Reactions

A small fraction of people vaccinated with mRNA-lipid nanoparticle (mRNA-LNP)-based COVID-19 vaccines display acute or subacute inflammatory symptoms whose mechanism has not been clarified to date. To better understand the molecular mechanism of these adverse events (AEs), here, we analyzed in vitro the vaccine-induced induction and interrelations of the following two major inflammatory processes: complement (C) activation and release of proinflammatory cytokines. Incubation of Pfizer-BioNTech's Comirnaty and Moderna's Spikevax with 75% human serum led to significant increases in C5a, sC5b-9, and Bb but not C4d, indicating C activation mainly via the alternative pathway. Control PEGylated liposomes (Doxebo) also induced C activation, but, on a weight basis, it was ~5 times less effective than that of Comirnaty. Viral or synthetic naked mRNAs had no C-activating effects. In peripheral blood mononuclear cell (PBMC) cultures supplemented with 20% autologous serum, besides C activation, Comirnaty induced the secretion of proinflammatory cytokines in the following order: IL-1α < IFN-γ < IL-1β < TNF-α < IL-6 < IL-8. Heat-inactivation of C in serum prevented a rise in IL-1α, IL-1β, and TNF-α, suggesting C-dependence of these cytokines' induction, although the C5 blocker Soliris and C1 inhibitor Berinert, which effectively inhibited C activation in both systems, did not suppress the release of any cytokines. These findings suggest that the inflammatory AEs of mRNA-LNP vaccines are due, at least in part, to stimulation of both arms of the innate immune system, whereupon C activation may be causally involved in the induction of some, but not all, inflammatory cytokines. Thus, the pharmacological attenuation of inflammatory AEs may not be achieved via monotherapy with the tested C inhibitors; efficacy may require combination therapy with different C inhibitors and/or other anti-inflammatory agents.

Characterisation of an anticomplement polysaccharide BP-S1 from seeds of Brucea javanica

Bioactivity-guided purification obtained polysaccharide BP-S1 from seeds of Brucea javanica. The results showed that BP-S1 was a homogenous polysaccharide with molecular weight of 45.7 kDa, mainly composed of arabinose and glucose in the ratio of 1.0:1.0 and the backbone of BP-S1 was deduced to be →3,4)-α-Glup-(1→ with branches of →2)-α-Arap-(1→and α-Arap-(1→, and the possible repetitive units were speculated according to result of methylation and 2D-NMR. Moreover, BP-S1 is a periodic rope-like structure. Functional analysis revealed that BP-S1 inhibited complement activation on the classic and alternative pathways with values of CH50 0.073 ± 0.012 mg/mL and AP50 0.097 ± 0.004 mg/mL, respectively. In mechanism study, using complement component depleted-sera methods indicated that BP-S1 selectively interacted with C3 and C4 components.

Large-scale separation of alkaloids from Corydalis decumbens by pH-zone-refining centrifugal partition chromatography and their anticomplement activity

Centrifugal partition chromatography in the pH-zone-refining mode was successfully applied to the separation of alkaloids from the crude extract of Corydalis decumbens. The experiment was performed with a two-phase solvent system composed of petroleum ether-ethyl acetate-ethanol-water (5:5:3:7, v/v/v/v) where triethylamine (10 mM) was added to the stationary phase and hydrochloric acid (10 mM) to the mobile phase. From 1.6 g of the crude extract, 43 mg protopine, 189 mg (+)-egenine, and 158 mg tetrahydropalmatine were obtained with a purity of 98.2%, 94.6%, and 96.7%, respectively. Tetrahydropalmatine showed an interesting anticomplement effect with CH50 0.11 and AP50 0.25 mg/mL, respectively. In a mechanistic study, tetrahydropalmatine interacted with C1, C3, C4, and C5 components in the complement activation cascade.

Iptacopan in Idiopathic Immune Complex-Mediated Membranoproliferative Glomerulonephritis: Protocol of the APPARENT Multicenter, Randomized Phase 3 Study

Introduction

Immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) is an ultra-rare, fast-progressing kidney disease that may be idiopathic (primary) or secondary to chronic infection, autoimmune disorders, or monoclonal gammopathies. Dysregulation of the alternative complement pathway is implicated in the pathophysiology of IC-MPGN; and currently, there are no approved targeted treatments. Iptacopan is an oral, highly potent proximal complement inhibitor that specifically binds to factor B and inhibits the alternative pathway (AP).

Methods

This randomized, double-blind, placebo-controlled phase 3 study (APPARENT; NCT05755386) will evaluate the efficacy and safety of iptacopan in patients with idiopathic (primary) IC-MPGN, enrolling up to 68 patients (minimum of 10 adolescents) aged 12 to 60 years with biopsy-confirmed IC-MPGN, proteinuria ≥1 g/g, and estimated glomerular filtration rate (eGFR) ≥30 ml/min per 1.73 m2. All patients will receive maximally tolerated angiotensin-converting enzyme inhibitor/angiotensin receptor blocker and vaccination against encapsulated bacteria. Patients with any organ transplant, progressive crescentic glomerulonephritis, or kidney biopsy with >50% interstitial fibrosis/tubular atrophy, will be excluded. Patients will be randomized 1:1 to receive either iptacopan 200 mg twice daily (bid) or placebo for 6 months, followed by open-label treatment with iptacopan 200 mg bid for all patients for 6 months. The primary objective of the study is to evaluate the efficacy of iptacopan versus placebo in proteinuria reduction measured as urine protein-to-creatinine ratio (UPCR) (24-h urine) at 6 months. Key secondary end points will assess kidney function measured by eGFR, patients who achieve a proteinuria-eGFR composite end point, and patient-reported fatigue.

Conclusion

This study will provide evidence toward the efficacy and safety of iptacopan in idiopathic (primary) IC-MPGN.

A bispecific inhibitor of complement and coagulation blocks activation in complementopathy models via a novel mechanism

Inhibitors of complement and coagulation are present in the saliva of a variety of blood-feeding arthropods that transmit parasitic and viral pathogens. Here, we describe the structure and mechanism of action of the sand fly salivary protein lufaxin, which inhibits the formation of the central alternative C3 convertase (C3bBb) and inhibits coagulation factor Xa (fXa). Surface plasmon resonance experiments show that lufaxin stabilizes the binding of serine protease factor B (FB) to C3b but does not detectably bind either C3b or FB alone. The crystal structure of the inhibitor reveals a novel all β-sheet fold containing 2 domains. A structure of the lufaxin-C3bB complex obtained via cryo-electron microscopy (EM) shows that lufaxin binds via its N-terminal domain at an interface containing elements of both C3b and FB. By occupying this spot, the inhibitor locks FB into a closed conformation in which proteolytic activation of FB by FD cannot occur. C3bB-bound lufaxin binds fXa at a separate site in its C-terminal domain. In the cryo-EM structure of a C3bB-lufaxin-fXa complex, the inhibitor binds to both targets simultaneously, and lufaxin inhibits fXa through substrate-like binding of a C-terminal peptide at the active site as well as other interactions in this region. Lufaxin inhibits complement activation in ex vivo models of atypical hemolytic uremic syndrome (aHUS) and paroxysmal nocturnal hemoglobinuria (PNH) as well as thrombin generation in plasma, providing a rationale for the development of a bispecific inhibitor to treat complement-related diseases in which thrombosis is a prominent manifestation.

Heme Interactions as Regulators of the Alternative Pathway Complement Responses and Implications for Heme-Associated Pathologies

Heme (Fe²⁺-protoporphyrin IX) is a pigment of life, and as a prosthetic group in several hemoproteins, it contributes to diverse critical cellular processes. While its intracellular levels are tightly regulated by networks of heme-binding proteins (HeBPs), labile heme can be hazardous through oxidative processes. In blood plasma, heme is scavenged by hemopexin (HPX), albumin and several other proteins, while it also interacts directly with complement components C1q, C3 and factor I. These direct interactions block the classical pathway (CP) and distort the alternative pathway (AP). Errors or flaws in heme metabolism, causing uncontrolled intracellular oxidative stress, can lead to several severe hematological disorders. Direct interactions of extracellular heme with alternative pathway complement components (APCCs) may be implicated molecularly in diverse conditions at sites of abnormal cell damage and vascular injury. In such disorders, a deregulated AP could be associated with the heme-mediated disruption of the physiological heparan sulphate-CFH coat of stressed cells and the induction of local hemostatic responses. Within this conceptual frame, a computational evaluation of HBMs (heme-binding motifs) aimed to determine how heme interacts with APCCs and whether these interactions are affected by genetic variation within putative HBMs. Combined computational analysis and database mining identified putative HBMs in all of the 16 APCCs examined, with 10 exhibiting disease-associated genetic (SNPs) and/or epigenetic variation (PTMs). Overall, this article indicates that among the pleiotropic roles of heme reviewed, the interactions of heme with APCCs could induce differential AP-mediated hemostasis-driven pathologies in certain individuals.

Targeted genotyping of COVID-19 patients reveals a signature of complement C3 and factor B coding SNPs associated with severe infection

We have attempted to explore further the involvement of complement components in the host COVID-19 (Coronavirus disease-19) immune responses by targeted genotyping of COVID-19 adult patients and analysis for missense coding Single Nucleotide Polymorphisms (coding SNPs) of genes encoding Alternative pathway (AP) components. We have identified a small group of common coding SNPs in Survivors and Deceased individuals, present in either relatively similar frequencies (CFH and CFI SNPs) or with stark differences in their relative abundance (C3 and CFB SNPs). In addition, we have identified several sporadic, potentially protective, coding SNPs of C3, CFB, CFD, CFH, CFHR1 and CFI in Survivors. No coding SNPs were detected for CD46 and CD55. Our demographic analysis indicated that the C3 rs1047286 or rs2230199 coding SNPs were present in 60 % of all the Deceased patients (n = 25) (the rs2230199 in 67 % of all Deceased Males) and in 31 % of all the Survivors (n = 105, p = 0.012) (the rs2230199 in 25 % of all Survivor Males). When we analysed these two major study groups using the presence of the C3 rs1047286 or rs2230199 SNPs as potential biomarkers, we noticed the complete absence of the protective CFB rs12614 and rs641153 coding SNPs from Deceased Males compared to Females (p = 0.0023). We propose that in these individuals, C3 carrying the R102G and CFB lacking the R32W or the R32Q amino acid substitutions, may contribute to enhanced association dynamics of the C3bBb AP pre-convertase complex assembly, thus enabling the exploitation of the activation of the Complement Alternative pathway (AP) by SARS-CoV-2.