Patterns of C1-Inhibitor/Plasma Serine Protease Complexes in Healthy Humans and in Hereditary Angioedema Patients

Elevated C1s/C1-INH in serum and plasma of myasthenia gravis patients

Myasthenia Gravis (MG) is an autoimmune neuromuscular disorder where acetylcholine receptor (AChR) antibodies induce membrane attack complex formation at the muscle membrane. The C1-inhibitor (C1-INH) regulates the classical pathway and is a promising marker in other autoimmune disorders. Treatment options for AChR antibody MG include complement inhibitors; nevertheless, the early pathway activation in MG remains unclear. Serum and plasma C1s-C1-INH levels were higher in MG patients than in matched healthy controls, supporting early classical pathway activation in most MG patients. These findings allow prospective validation studies of activated C1s as a putative treatment target and potential accompanying biomarker in MG.

Inter-α-trypsin inhibitor heavy chain 4 (ITIH4) as a compensatory protease inhibitor in hereditary angioedema

BACKGROUND

Hereditary angioedema (HAE) is a genetic disorder that manifests as recurrent angioedema attacks, most frequently due to absent or reduced C1 inhibitor (C1INH) activity. C1INH is a crucial regulator of enzymatic cascades in the complement, fibrinolytic, and contact systems. Inter-α-trypsin inhibitor heavy chain 4 (ITIH4) is an abundant plasma protease inhibitor that can inhibit enzymes in the proteolytic pathways associated with HAE. Nothing is known about its role in HAE.

OBJECTIVE

We investigated ITIH4 activation in HAE, establishing it as a potential biomarker, and explored its involvement in HAE-associated proteolytic pathways.

METHODS

Specific immunoassays for noncleaved ITIH4 (intact ITIH4) and an assay detecting both intact and cleaved ITIH4 (total ITIH4) were developed. We initially tested serum samples from HAE patients (n = 20), angiotensin-converting enzyme inhibitor-induced edema patients (ACEI) (n = 20), and patients with HAE of unknown cause (HAE-UNK) (n = 20). Validation involved an extended cohort of 80 HAE patients (60 with HAE-C1INH type 1, 20 with HAE-C1INH type 2), including samples taken during attack and quiescent disease periods, as well as samples from 100 healthy controls.

RESULTS

In 63% of HAE patients, intact ITIH4 assay showed lower signals than total ITIH4 assay. This difference was not observed in ACEI and HAE-UNK patients. Western blot analysis confirmed cleaved ITIH4 with low intact ITIH4 samples. In serum samples lacking intact endogenous ITIH4, we observed immediate cleavage of added recombinant ITIH4, suggesting continuous enzymatic activity in the serum. Confirmatory HAE cohort analysis revealed significantly lower intact ITIH4 levels in both type 1 and type 2 HAE patients compared to controls, with consistently low intact/total ITIH4 ratios during clinical HAE attacks.

CONCLUSION

The disease-specific low intact ITIH4 levels highlight its unique nature in HAE. ITIH4 may exhibit compensatory mechanisms in HAE, suggesting its utility as a diagnostic and prognostic biomarker. The variations during quiescent and active disease periods raise intriguing questions about the dynamics of proteolytic pathways in HAE.

sMR and PTX3 levels associate with COVID-19 outcome and survival but not with Long COVID

Biomarkers for monitoring COVID-19 disease course are lacking. Study aim was to identify biomarkers associated with disease severity, survival, long-term outcome, and Long COVID. As excessive macrophages activation is a hallmark of COVID-19 and complement activation is key in this, we selected the following proteins involved in these processes: PTX3, C1q, C1-INH, C1s/C1-INH, and sMR. EDTA-plasma concentrations were measured in 215 patients and 47 controls using ELISA. PTX3, sMR, C1-INH, and C1s/C1-INH levels were associated with disease severity. PTX3 and sMR were also associated with survival and long-term immune recovery. Lastly, sMR levels associate with ICU admittance. sMR (AUC 0.85) and PTX3 (AUC 0.78) are good markers for disease severity, especially when used in combination (AUC 0.88). No association between biomarker levels and Long COVID was observed. sMR has not previously been associated with COVID-19 disease severity, ICU admittance or survival and may serve as marker for disease course.

Humoral complementomics - exploration of noninvasive complement biomarkers as predictors of renal cancer progression

Despite the progress of anti-cancer treatment, the prognosis of many patients with solid tumors is still dismal. Reliable noninvasive biomarkers are needed to predict patient survival and therapy response. Here, we propose a Humoral Complementomics approach: a work-up of assays to comprehensively evaluate complement proteins, activation fragments, and autoantibodies targeting complement proteins in plasma, which we correlated with the intratumoral complement activation, and/or local production, focusing on localized and metastatic clear cell renal cell carcinoma (ccRCC). In two prospective ccRCC cohorts, plasma C2, C5, Factor D and properdin were elevated compared to healthy controls, reflecting an inflammatory phenotype that correlated with plasma calprotectin levels but did not associate with CRP or with patient prognosis. Conversely, autoantibodies against the complement C3 and the reduced form of FH (a tumor neo-epitope reported in lung cancer) correlated with a favorable outcome. Our findings pointed to a specific group of patients with elevated plasma C4d and C1s-C1INH complexes, indicating the initiation of the classical pathway, along with elevated Ba and Bb, indicating alternative pathway activation. Boostrapped Lasso regularized Cox regression revealed that the most predictive complement biomarkers were elevated plasma C4d and Bb levels at the time of surgery, which correlated with poor prognosis. In conclusion, we propose Humoral Complementomics as an unbiased approach to study the global state of the complement system in any pathological plasma sample and disease context. Its implementation for ccRCC revealed that elevated C4d and Bb in plasma are promising prognostic biomarkers, correlating with shorter progression-free survival.

The Lectin Pathway of the Complement System-Activation, Regulation, Disease Connections and Interplay with Other (Proteolytic) Systems

The complement system is the other major proteolytic cascade in the blood of vertebrates besides the coagulation-fibrinolytic system. Among the three main activation routes of complement, the lectin pathway (LP) has been discovered the latest, and it is still the subject of intense research. Mannose-binding lectin (MBL), other collectins, and ficolins are collectively termed as the pattern recognition molecules (PRMs) of the LP, and they are responsible for targeting LP activation to molecular patterns, e.g., on bacteria. MBL-associated serine proteases (MASPs) are the effectors, while MBL-associated proteins (MAps) have regulatory functions. Two serine protease components, MASP-1 and MASP-2, trigger the LP activation, while the third component, MASP-3, is involved in the function of the alternative pathway (AP) of complement. Besides their functions within the complement system, certain LP components have secondary ("moonlighting") functions, e.g., in embryonic development. They also contribute to blood coagulation, and some might have tumor suppressing roles. Uncontrolled complement activation can contribute to the progression of many diseases (e.g., stroke, kidney diseases, thrombotic complications, and COVID-19). In most cases, the lectin pathway has also been implicated. In this review, we summarize the history of the lectin pathway, introduce their components, describe its activation and regulation, its roles within the complement cascade, its connections to blood coagulation, and its direct cellular effects. Special emphasis is placed on disease connections and the non-canonical functions of LP components.

Proteomic Comparisons of Caprine Milk Whole Cream Buttermilk Whey and Cheese Whey Cream Buttermilk

Buttermilk, a potential material used to produce milk fat globule membrane (MFGM), is obtained as a byproduct of butter making from milk whole cream and cheese whey cream. This study investigated the effects of rennet and acid coagulation on the protein profiles of buttermilk rennet-coagulated whey (BRW) and buttermilk acid-coagulated whey (BAW). They were compared to those of whey cream buttermilk (WCB). Rennet coagulation was more efficient in removing casein, while retaining more IgG and lactoferrin than acid coagulation. BRW had more MFGM than BAW. Butyrophilin, xanthine dehydrogenase, and mucin1 were significantly higher (P < 0.05) in BRW, while fatty acid-binding protein 3 was enriched in BAW. KEGG analysis showed that complement and coagulation cascades had the greatest differences, and the abundance of proteins involved in this signaling pathway in BRW and BAW was higher, suggesting their potential anticoagulant and anti-inflammatory activity. BAW had higher apolipoprotein A4 and transcobalamin 2, which are essential carriers for transporting long-chain fatty acids and vitamin B12 from the intestine to the blood. Therefore, BAW intake might improve lipids and vitamin B12 absorption. This study can help deepen the understanding of protein composition of MFGM-enriched whey and facilitate the production of MFGM proteins for infants and old-aged populations.

Restriction of C1-inhibitor activity in hereditary angioedema by dominant-negative effects of disease-associated SERPING1 gene variants

BACKGROUND

Patients with hereditary angioedema experience recurrent, sometimes life-threatening, attacks of edema. It is a rare genetic disorder characterized by genetic and clinical heterogenicity. Most cases are caused by genetic variants in the SERPING1 gene leading to plasma deficiency of the encoded protein C1 inhibitor (C1INH). More than 500 different hereditary angioedema-causing variants have been identified in the SERPING1 gene, but the disease mechanisms by which they result in pathologically low C1INH plasma levels remain largely unknown.

OBJECTIVES

The aim was to describe trans-inhibitory effects of full-length or near full-length C1INH encoded by 28 disease-associated SERPING1 variants.

METHODS

HeLa cells were transfected with expression constructs encoding the studied SERPING1 variants. Extensive and comparative studies of C1INH expression, secretion, functionality, and intracellular localization were carried out.

RESULTS

Our findings characterized functional properties of a subset of SERPING1 variants allowing the examined variants to be subdivided into 5 different clusters, each containing variants sharing specific molecular characteristics. For all variants except 2, we found that coexpression of mutant and normal C1INH negatively affected the overall capacity to target proteases. Strikingly, for a subset of variants, intracellular formation of C1INH foci was detectable only in heterozygous configurations enabling simultaneous expression of normal and mutant C1INH.

CONCLUSIONS

We provide a functional classification of SERPING1 gene variants suggesting that different SERPING1 variants drive the pathogenicity through different and in some cases overlapping molecular disease mechanisms. For a subset of gene variants, our data define some types of hereditary angioedema with C1INH deficiency as serpinopathies driven by dominant-negative disease mechanisms.

Contact system and intrinsic pathway activation in patients with advanced pancreatic cancer: a prospective cohort study

BACKGROUND

Despite high risk of venous thromboembolism (VTE) in patients with pancreatic cancer, there are little data on contact system activation in these patients.

OBJECTIVES

To quantify contact system and intrinsic pathway activation and subsequent VTE risk in patients with pancreatic cancer.

METHODS

Patients with advanced pancreatic cancer were compared with controls. Blood was drawn at baseline and patients were followed for 6 months. Complexes of proteases with their natural inhibitors, C1-esterase inhibitor (C1-INH), antithrombin (AT), or alpha-1 antitrypsin (α1at), were measured for complexes containing kallikrein (PKa:C1-INH), factor (F)XIIa (FXIIa:C1-INH), and FXIa (FXIa:C1-INH, FXIa:AT, FXIa:α1at). The association of cancer with complex levels was assessed in a linear regression model, adjusted for age, sex, and body mass index. In a competing risk regression model, we assessed associations between complex levels and VTE.

RESULTS

One hundred nine patients with pancreatic cancer and 22 controls were included. The mean age was 66 years (SD, 8.4) in the cancer cohort and 52 years (SD, 10.1) in controls. In the cancer cohort, 18 (16.7%) patients developed VTE during follow-up. In the multivariable regression model, pancreatic cancer was associated with increased complexes of PKa:C1-INH (P < .001), FXIa:C1-INH (P < .001), and FXIa:AT (P < .001). High FXIa:α1at (subdistribution hazard ratio, 1.48 per log increase; 95% CI, 1.02-2.16) and FXIa:AT (subdistribution hazard ratio, 2.78 highest vs lower quartiles; 95% CI, 1.10-7.00) were associated with VTE.

CONCLUSION

Complexes of proteases with their natural inhibitors were elevated in patients with cancer. These data suggest that the contact system and intrinsic pathway activation are increased in patients with pancreatic cancer.

Patient-physician interactions in hereditary angioedema-Key learnings from the coronavirus disease 2019 pandemic

BACKGROUND

The coronavirus disease pandemic and its containing measures have caused concerns for patients with hereditary angioedema (HAE) and their treating physicians. Both faced challenges surrounding interaction, and communication had to adapt to facilitate appropriate management. Specifically, the pandemic resulted in reduced in-person contact in clinics. Where possible, telemedicine appointments were offered and treatment outside the hospital setting was encouraged. BODY: The pandemic markedly affected patient-physician communication, which is essential to maintain partnerships and optimize care. Although patients with HAE are often experts in their condition, guidance by their physicians is essential, especially with the recent shift toward patient-centered management for rare diseases and shared decision-making (SDM). SDM enables patients to take control of their disease and allows the risks and benefits of treatment to be discussed with their physicians. This review explores perspectives from patients and physicians in the HAE clinical setting, particularly regarding their experiences with communication throughout the pandemic. We discuss the importance of SDM in rare diseases such as HAE, factors that impact effective communication, and potential solutions.

CONCLUSION

Since patient-centered care and SDM have particular relevance in rare diseases in general, we believe our findings could be transferrable and applicable in the management of other rare diseases.

Decreased adhesion to endothelium leads to elevated neutrophil granulocyte count in hereditary angioedema patients

As many aspects of hereditary angioedema (HAE) due to C1-inhibitor (C1-INH) deficiency (C1-INH-HAE) cannot be explained with elevated bradykinin level alone, it has recently become clear that other factors also play an important role in the pathogenesis. One of these factors could be elevated neutrophil granulocyte (NG) counts, which are associated with increased NG activation in C1-INH-HAE patients; however, their origin has not been elucidated so far. Here, we aimed to investigate whether the excess of NGs is due to disturbed maturation, biased circulating/marginated pool equilibrium or decreased elimination. We enrolled 20 attack-free C1-INH-HAE patients together with 21 healthy controls and collected blood samples. We compared cell surface maturation markers, adhesion molecules, cytokine receptors, and Ca2+-mobilization of NG by flow cytometry, activation markers by ELISA, and NG/endothelial cell adhesion by automated pipetting system. Cell-surface markers showed normal maturation of NGs in C1-INH-HAE patients. Adhesion of NGs to endothelial cells pretreated with lipopolysaccharide or phorbol 12-myristate 13-acetate was significantly weaker in samples from C1-INH-HAE patients and bradykinin had no effect on the adhesion. NGs from C1-INH-HAE patients were in an activated state when assessed by soluble activation markers without any stimulation. Our data support that the maturation of NGs in C1-INH-HAE patients is normal, whereas adhesion properties of patient-derived NGs to the endothelium are reduced compared to those from healthy controls, indicating a bias between the circulating and marginated pools of NGs in patients. Bradykinin may not be responsible for reduced adhesion properties of NGs.

Protein Corona of Anionic Fluid-Phase Liposomes Compromises Their Integrity Rather than Uptake by Cells

Despite the undisputable role of the protein corona in the biointeractions of liposome drug carriers, the field suffers from a lack of knowledge regarding the patterns of protein deposition on lipid surfaces with different compositions. Here, we investigated the protein coronas formed on liposomes of basic compositions containing combinations of egg phosphatidylcholine (PC), palmitoyloleoyl phosphatidylglycerol (POPG), and cholesterol. Liposome-protein complexes isolated by size-exclusion chromatography were delipidated and analyzed using label-free LC-MS/MS. The addition of the anionic lipid and cholesterol both affected the relative protein abundances (and not the total bound proteins) in the coronas. Highly anionic liposomes, namely those containing 40% POPG, carried corona enriched with cationic proteins (apolipoprotein C1, beta-2-glycoprotein 1, and cathelicidins) and were the least stable in the calcein release assay. Cholesterol improved the liposome stability in the plasma. However, the differences in the corona compositions had little effect on the liposome uptake by endothelial (EA.hy926) and phagocytic cells in the culture (U937) or ex vivo (blood-derived monocytes and neutrophils). The findings emphasize that the effect of protein corona on the performance of the liposomes as drug carriers occurs through compromising particle stability rather than interfering with cellular uptake.

Insights into the pathogenesis of hereditary angioedema using genetic sequencing and recombinant protein expression analyses

BACKGROUND

The pathogenesis of hereditary angioedema (HAE) type I and type II is linked to defective C1 esterase inhibitor (C1-INH) encoded by the SERPING1 gene. There are substantial variabilities in the clinical presentations of patients with HAE that are not directly correlated to the serum levels of C1-INH. The impact of SERPING1 variants on C1-INH expression, structure, and function is incompletely understood.

OBJECTIVE

To investigate the influence of SERPING1 variants on the C1-INH expression, structure, and function of 20 patients with HAE from 14 families with no prior genetic diagnosis.

METHODS

Patients underwent whole-exome sequencing (WES). If no variants were identified, whole-genome sequencing (WGS) was performed. Except for the frameshift and large deletions, each C1-INH variant was recombinantly produced and, if synthesized and secreted, was subjected to structural, oligosaccharide, and functional analyses.

RESULTS

We identified 11 heterozygous variants in the SERPING1 gene, of which 5 were classified as pathogenic (E85Dfs∗63, N166Qfs∗91, K201Qfs∗56, P399A, and R466H) and 6 as variants of uncertain significance (C130W, I224S, N272del, K273del, L349F, and F471C). Three large heterozygous deletions were discovered through WGS. Our data indicate that C130W, N272del, P399A, and F471C are poorly synthesized, I224S prevents proper C1-INH folding, and K273del impairs C1-INH function by adding an additional oligosaccharide. Further evaluation suggests that compound variant P399A/L349F contributes to a more severe clinical phenotype.

CONCLUSIONS

Our combined approach of WES and WGS uncovered SERPING1 gene alternations in each patient. The recombinant protein production followed by systematic antigenic, structural, and functional assessment facilitates the identification of underlying pathogenic mechanisms in HAE.

C1-inhibitor/C1-inhibitor antibody complexes in acquired angioedema due to C1-inhibitor deficiency

BACKGROUND

Autoantibodies against C1-inhibitor (C1-INH-Ab) have a diagnostic value in acquired angioedema due to C1-inhibitor deficiency (C1-INH-AAE), even though antibodies can circulate in complexes, which can be undetectable by proven methods. Our aim was to measure C1-INH/C1-INH-Ab complexes (CAC) and investigate their connection to C1-INH-Ab and the changes in their titer over time.

RESULTS

19 patients were diagnosed with C1-INH-AAE in the Hungarian Angioedema Center of Reference and Excellence; 79% of them had an underlying disease. Samples were examined with a newly developed in-house complex ELISA method. Patients with high C1-INH-Ab titer had a CAC titer which did not exceed the normal level and the ones with high CAC titer had a C1-INH-Ab titer which did not exceed the normal level. In case of those patients who had C1-INH-Ab and CAC of the same type of immunoglobulin, the increasing titer of C1-INH-Ab went together with the decreasing level of CAC and vice versa. CAC titer was already increased before the diagnosis of the underlying disease.

CONCLUSIONS

Free circulating and complex antibodies are in a dynamically changing equilibrium. CAC measurements can help to predict the development of an underlying disease. The efficiency of the treatment for underlying disease can be monitored by the decreasing CAC titers. Our results show that the CAC can be of important additional information besides the complement panel examination in case of C1-INH-AAE. Measurement of CAC is recommended to be done parallelly with C1-INH-Ab, so as to detect both free and bound antibodies.

"Super" SERPINs-A stabilizing force against fibrinolysis in thromboinflammatory conditions

The superfamily of serine protease inhibitors (SERPINs) are a class of inhibitors that utilise a dynamic conformational change to trap and inhibit their target enzymes. Their powerful nature lends itself well to regulation of complex physiological enzymatic cascades, such as the haemostatic, inflammatory and complement pathways. The SERPINs α2-antiplasmin, plasminogen-activator inhibitor-1, plasminogen-activator inhibitor-2, protease nexin-1, and C1-inhibitor play crucial inhibitory roles in regulation of the fibrinolytic system and inflammation. Elevated levels of these SERPINs are associated with increased risk of thrombotic complications, obesity, type 2 diabetes, and hypertension. Conversely, deficiencies of these SERPINs have been linked to hyperfibrinolysis with bleeding and angioedema. In recent years SERPINs have been implicated in the modulation of the immune response and various thromboinflammatory conditions, such as sepsis and COVID-19. Here, we highlight the current understanding of the physiological role of SERPINs in haemostasis and inflammatory disease progression, with emphasis on the fibrinolytic pathway, and how this becomes dysregulated during disease. Finally, we consider the role of these SERPINs as potential biomarkers of disease progression and therapeutic targets for thromboinflammatory diseases.

Safety Aspects and Rational Use of Lanadelumab Injections in the Treatment of Hereditary Angioedema (HAE): Clinical Insights

Hereditary angioedema (HAE) is a rare genetic disorder characterized by recurrent episodes of skin/mucosal swelling, and/or attacks of severe abdominal pain when it affects the gastrointestinal tract. The disease might be unexpectedly fatal when the upper airways are compromised. HAE clinical presentation, disease course and prognosis are associated with significant disease burden and severely impaired quality of life. Lanadelumab is a breakthrough therapy for the prevention of attacks in HAE type 1 and 2 patients. This revolutionary approach to administer a single subcutaneous injection (once every two to four weeks) and achieve complete disease control has dramatically improved patient care resulting in significant change in the life of affected families. Current data support the drug's tolerability in adult and adolescent patients without notable safety concerns in both clinical research and real-world settings. Rational use of prophylactic treatments of HAE searches for a socio-economic balance, taking into account the life-long course of the disease, the public health funds who pay the monetary price, and the patients who might need to receive the therapy for a period longer than investigated during the development program. In this review, we address the current evidence on lanadelumab's tolerability, highlighting aspects of the drug's rationale use in clinical practice. Further studies need to investigate whether this therapy might be appropriate in other forms of angioedema, such as idiopathic primary angioedema and HAE with normal C1 inhibitor. Future efforts must focus to improve modern drugs' accessibility in more countries. Although modern prophylactic options lessen the risk of fatal laryngeal attacks, patients must be equipped with reliable on-demand therapies and be trained how to use them as such a risk cannot be fully diminished with potentially life-threatening attacks occurring even in subjects with successful and stable long-term prophylaxis. Notwithstanding, further studies are needed to identify early responders from non-responders and develop therapies for the latter.

SerpinG1: A Novel Biomarker Associated With Poor Coronary Collateral in Patients With Stable Coronary Disease and Chronic Total Occlusion

Background This study aimed to explore predictive biomarkers of coronary collateralization in patients with chronic total occlusion. Methods and Results By using a microarray expression profiling program downloaded from the Gene Expression Omnibus database, weighted gene coexpression network analysis was constructed to analyze the relationship between potential modules and coronary collateralization and screen out the hub genes. Then, the hub gene was identified and validated in an independent cohort of patients (including 299 patients with good arteriogenic responders and 223 patients with poor arteriogenic responders). Weighted gene coexpression network analysis showed that SERPING1 in the light-cyan module was the only gene that was highly correlated with both the gene module and the clinical traits. Serum levels of serpinG1 were significantly higher in patients with bad arteriogenic responders than in patients with good arteriogenic responders (472.53±197.16 versus 314.80±208.92 μg/mL; P<0.001) and were negatively associated with the Rentrop score (Spearman r=-0.50; P<0.001). Receiver operating characteristic curve analysis indicated that the area under the curve was 0.77 (95% CI, 0.72-0.81; P<0.001) for serum serpinG1 in prediction of bad arteriogenic responders. After adjusting for traditional cardiovascular risk factors, serum serpinG1 levels (per SD) remained an independent risk factor for bad arteriogenic responders (odds ratio, 2.20 [95% CI, 1.76-2.74]; P<0.001). Conclusions Our findings illustrate that SERPING1 screened by weighted gene coexpression network analysis was associated with poor collateralization in patients with chronic total occlusion.

Distinction of early complement classical and lectin pathway activation via quantification of C1s/C1-INH and MASP-1/C1-INH complexes using novel ELISAs

The most commonly used markers to assess complement activation are split products that are produced through activation of all three pathways and are located downstream of C3. In contrast, C4d derives from the cleavage of C4 and indicates either classical (CP) or lectin pathway (LP) activation. Although C4d is perfectly able to distinguish between CP/LP and alternative pathway (AP) activation, no well-established markers are available to differentiate between early CP and LP activation. Active enzymes of both pathways (C1s/C1r for the CP, MASP-1/MASP-2 for the LP) are regulated by C1 esterase inhibitor (C1-INH) through the formation of covalent complexes. Aim of this study was to develop validated immunoassays detecting C1s/C1-INH and MASP-1/C1-INH complex levels. Measurement of the complexes reveals information about the involvement of the respective pathways in complement-mediated diseases. Two sandwich ELISAs detecting C1s/C1-INH and MASP-1/C1-INH complex were developed and tested thoroughly, and it was investigated whether C1s/C1-INH and MASP-1/C1-INH complexes could serve as markers for either early CP or LP activation. In addition, a reference range for these complexes in healthy adults was defined, and the assays were clinically validated utilizing samples of 414 COVID-19 patients and 96 healthy controls. The immunoassays can reliably measure C1s/C1-INH and MASP-1/C1-INH complex concentrations in EDTA plasma from healthy and diseased individuals. Both complex levels are increased in serum when activated with zymosan, making them suitable markers for early classical and early lectin pathway activation. Furthermore, measurements of C1-INH complexes in 96 healthy adults showed normally distributed C1s/C1-INH complex levels with a physiological concentration of 1846 ± 1060 ng/mL (mean ± 2SD) and right-skewed distribution of MASP-1/C1-INH complex levels with a median concentration of 36.9 (13.18 - 87.89) ng/mL (2.5-97.5 percentile range), while levels of both complexes were increased in COVID-19 patients (p<0.0001). The newly developed assays measure C1-INH complex levels in an accurate way. C1s/C1-INH and MASP-1/C1-INH complexes are suitable markers to assess early classical and lectin pathway activation. An initial reference range was set and first studies showed that these markers have added value for investigating and unraveling complement activation in human disease.

Diagnosing Pediatric Patients With Hereditary C1-Inhibitor Deficiency—Experience From the Hungarian Angioedema Center of Reference and Excellence

Background

Hereditary Angioedema with C1-inhibitor deficiency (C1-INH-HAE) is a rare disease characterized by recurrent subcutaneous and/or submucosal edematous (HAE) episodes, which may occur at any age. The mean age of the symptom onset is 10–12 years. Diagnostic protocols differ by age group and family history.

Methods

We retrospectively analyzed clinical and laboratory data (C4-, C1-INH concentration and function) from 49 pediatric patients diagnosed with C1-INH deficiency at our Angioedema Center between 2001 and 2020. Moreover, we analyzed the connection between complement parameters and symptom onset.

Results

From the 49 pediatric patients [boy/girl: 23/26, the average age of diagnosis: 6.7 years (min: 0-max: 18.84)], the majority (36/49, 73%) was diagnosed as the result of family screening. Of all the enrolled patients, 34% (17/49) experienced symptoms before the diagnosis. During the observational period, 33% (16/49) of the patients remained asymptomatic, while 33% (16/49) became symptomatic. The average age at symptom onset was 7.8 years (min: 0.5–max: 18). Only 27% (13/49) of pediatric patients were diagnosed after referrals to our center because of typical symptoms. From those patients diagnosed with family screening, 4/36 experienced symptoms at or before the time of the diagnosis. In the case of five newborns from the family screening group, umbilical cord blood samples were used for complement testing. In the case of 3/36 patients, the first complement parameters did not clearly support the disease, but the presence of the mutation identified in the family verified the diagnosis. Complement results were available from 11 patients who became symptomatic during the observational period. Complement parameters 1 year prior to and after the onset of symptoms were compared, and significantly lower concentrations of C1-INH (p = 0.0078) were detected after the onset of symptoms compared to the preceding (symptom-free) period.

Discussion

The majority of pediatric patients were diagnosed as a result of family screening before the onset of symptoms. Early diagnosis allows supplying the patients with special acute treatment for HAE attacks, which may occur at any time. Our results highlight the importance of DNA analysis in pediatric patients in case of a known mutation in the family, and an ambiguous result of complement testing.

Component 1 Inhibitor Missense (Val480Met) Variant Is Associated With Gene Expression and Sepsis Development in Neonatal Lung Disease

BACKGROUND

Neonatal lung disease has a multifaceted etiopathology, including an explosive inflammatory sequence in the immature lung. Complement component 1 Esterase INHibitor (C1INH) is implicated in controlling inflammation in response to infection/injury.

AIM

To explore for the first time the association of the C1INH rs4926 (Val480Met) variant and circulatory transcript expression levels in the neonates that had evidence of lung disease and the clinic-laboratory data.

METHODS

A total of 139 unrelated neonates were enrolled in this case-control study. C1INH genotyping and expression analyses were done using TaqMan Genotyping and Real-Time qPCR, respectively.

RESULTS

A/A genotype carriers were two times more likely to develop in newborns with lung disease under homozygote (A/A vs. G/G: OR = 2.66, 95%CI = 1.03-6.87, p = 0.039) and recessive (A/A vs. G/G-A/G: OR = 2.42, 95%CI = 1.07-6.06, p = 0.047) models. Also, a higher frequency of A/A genotype was observed in the patient's cohort complicated with sepsis (44.2 vs. 14.3%, p = 0.002). Neonates with lung disease with A variant had more risk for developing sepsis under homozygote (A/A vs. G/G: OR = 5.19, 95%CI = 1.73-15.6, p = 0.002), dominant (A/G-A/A vs. G/G: OR = 2.39, 95%CI = 1.02-5.58, p = 0.041), and recessive (A/A vs. G/G-A/G: OR = 5.38, 95%CI = 1.86-15.5, p < 0.001) models. Regression analysis revealed rs4926^*A/A genotype as an independent predictor risk factor for sepsis development in cohorts with lung disease (adjusted OR = 4.26, 95%CI = 1.38-13.1, p = 0.012). The circulatory transcript was significantly downregulated in neonates with lung disease in whom rs4926^*A/A carriers had the least expression levels (median: -2.86, IQR: -3.55 to -1.71; p < 0.001). ROC curve analysis revealed C1INH expression could differentiate between cohorts with/without subsequent development of sepsis, and the discrimination ability was enhanced when combined with circulatory IL-6 and CRP levels (AUC = 0.926, 95%CI = 0.87-0.97).

CONCLUSION

The C1INH rs4926 variant might play an essential role in the susceptibility to neonatal lung disease and could predict sepsis development in this cohort. Furthermore, the circulatory expression levels of this gene were downregulated in the neonatal lung disease cohort, supporting its potential role in the pathophysiology of this disorder, and highlighting its promising role in future targeted therapy.

COVID-19, Pre-Eclampsia, and Complement System

COVID-19 is characterized by virus-induced injury leading to multi-organ failure, together with inflammatory reaction, endothelial cell (EC) injury, and prothrombotic coagulopathy with thrombotic events. Complement system (C) via its cross-talk with the contact and coagulation systems contributes significantly to the severity and pathological consequences due to SARS-CoV-2 infection. These immunopathological mechanisms overlap in COVID-19 and pre-eclampsia (PE). Thus, mothers contracting SARS-CoV-2 infection during pregnancy are more vulnerable to developing PE. SARS-CoV-2 infection of ECs, via its receptor ACE2 and co-receptor TMPRSS2, can provoke endothelial dysfunction and disruption of vascular integrity, causing hyperinflammation and hypercoagulability. This is aggravated by bradykinin increase due to inhibition of ACE2 activity by the virus. C is important for the progression of normal pregnancy, and its dysregulation can impact in the form of PE-like syndrome as a consequence of SARS-CoV-2 infection. Thus, there is also an overlap between treatment regimens of COVID-19 and PE. C inhibitors, especially those targeting C3 or MASP-2, are exciting options for treating COVID-19 and consequent PE. In this review, we examine the role of C, contact and coagulation systems as well as endothelial hyperactivation with respect to SARS-CoV-2 infection during pregnancy and likely development of PE.

Expanding Horizons in Complement Analysis and Quality Control

Complement not only plays a key role in host microbial defense but also modulates the adaptive immune response through modification of T- and B-cell reactivity. Moreover, a normally functioning complement system participates in hematopoiesis, reproduction, lipid metabolism, and tissue regeneration. Because of its powerful inflammatory potential, multiple regulatory proteins are needed to prevent potential tissue damage. In clinical practice, dysregulation and overactivation of the complement system are major causes of a variety of inflammatory and autoimmune diseases ranging from nephropathies, age-related macular degeneration (AMD), and systemic lupus erythematosus (SLE) to graft rejection, sepsis, and multi-organ failure. The clinical importance is reflected by the recent development of multiple drugs targeting complement with a broad spectrum of indications. The recognition of the role of complement in diverse diseases and the advent of complement therapeutics has increased the number of laboratories and suppliers entering the field. This has highlighted the need for reliable complement testing. The relatively rapid expansion in complement testing has presented challenges for a previously niche field. This is exemplified by the issue of cross-reactivity of complement-directed antibodies and by the challenges of the poor stability of many of the complement analytes. The complex nature of complement testing and increasing clinical demand has been met in the last decade by efforts to improve the standardization among laboratories. Initiated by the IUIS/ICS Committee for the Standardization and Quality Assessment in Complement Measurements 14 rounds of external quality assessment since 2010 resulted in improvements in the consistency of testing across participating institutions, while extending the global reach of the efforts to more than 200 laboratories in 30 countries. Worldwide trends of assay availability, usage, and analytical performance are summarized based on the past years’ experiences. Progress in complement analysis has been facilitated by the quality assessment and standardization efforts that now allow complement testing to provide a comprehensive insight into deficiencies and the activation state of the system. This in turn enables clinicians to better define disease severity, evolution, and response to therapy.

Proteomics and Machine Learning Approaches Reveal a Set of Prognostic Markers for COVID-19 Severity With Drug Repurposing Potential

The pestilential pathogen SARS-CoV-2 has led to a seemingly ceaseless pandemic of COVID-19. The healthcare sector is under a tremendous burden, thus necessitating the prognosis of COVID-19 severity. This in-depth study of plasma proteome alteration provides insights into the host physiological response towards the infection and also reveals the potential prognostic markers of the disease. Using label-free quantitative proteomics, we performed deep plasma proteome analysis in a cohort of 71 patients (20 COVID-19 negative, 18 COVID-19 non-severe, and 33 severe) to understand the disease dynamics. Of the 1200 proteins detected in the patient plasma, 38 proteins were identified to be differentially expressed between non-severe and severe groups. The altered plasma proteome revealed significant dysregulation in the pathways related to peptidase activity, regulated exocytosis, blood coagulation, complement activation, leukocyte activation involved in immune response, and response to glucocorticoid biological processes in severe cases of SARS-CoV-2 infection. Furthermore, we employed supervised machine learning (ML) approaches using a linear support vector machine model to identify the classifiers of patients with non-severe and severe COVID-19. The model used a selected panel of 20 proteins and classified the samples based on the severity with a classification accuracy of 0.84. Putative biomarkers such as angiotensinogen and SERPING1 and ML-derived classifiers including the apolipoprotein B, SERPINA3, and fibrinogen gamma chain were validated by targeted mass spectrometry-based multiple reaction monitoring (MRM) assays. We also employed an in silico screening approach against the identified target proteins for the therapeutic management of COVID-19. We shortlisted two FDA-approved drugs, namely, selinexor and ponatinib, which showed the potential of being repurposed for COVID-19 therapeutics. Overall, this is the first most comprehensive plasma proteome investigation of COVID-19 patients from the Indian population, and provides a set of potential biomarkers for the disease severity progression and targets for therapeutic interventions.

Molecular Basis for Bordetella pertussis Interference with Complement, Coagulation, Fibrinolytic, and Contact Activation Systems: the Cryo-EM Structure of the Vag8-C1 Inhibitor Complex

Complement, contact activation, coagulation, and fibrinolysis are serum protein cascades that need strict regulation to maintain human health. Serum glycoprotein, a C1 inhibitor (C1-INH), is a key regulator (inhibitor) of serine proteases of all the above-mentioned pathways. Recently, an autotransporter protein, virulence-associated gene 8 (Vag8), produced by the whooping cough pathogen, Bordetella pertussis, was shown to bind to C1-INH and interfere with its function. Here, we present the structure of the Vag8-C1-INH complex determined using cryo-electron microscopy at a 3.6-Å resolution. The structure shows a unique mechanism of C1-INH inhibition not employed by other pathogens, where Vag8 sequesters the reactive center loop of C1-INH, preventing its interaction with the target proteases.IMPORTANCE The structure of a 10-kDa protein complex is one of the smallest to be determined using cryo-electron microscopy at high resolution. The structure reveals that C1-INH is sequestered in an inactivated state by burial of the reactive center loop in Vag8. By so doing, the bacterium is able to simultaneously perturb the many pathways regulated by C1-INH. Virulence mechanisms such as the one described here assume more importance given the emerging evidence about dysregulation of contact activation, coagulation, and fibrinolysis leading to COVID-19 pneumonia.

MASPs at the crossroad between the complement and the coagulation cascades - the case for COVID-19

Components of the complement system and atypical parameters of coagulation were reported in COVID-19 patients, as well as the exacerbation of the inflammation and coagulation activity. Mannose binding lectin (MBL)- associated serine proteases (MASPs) play an important role in viral recognition and subsequent activation of the lectin pathway of the complement system and blood coagulation, connecting both processes. Genetic variants of MASP1 and MASP2 genes are further associated with different levels and functional efficiency of their encoded proteins, modulating susceptibility and severity to diseases. Our review highlights the possible role of MASPs in SARS-COV-2 binding and activation of the lectin pathway and blood coagulation cascades, as well as their associations with comorbidities of COVID-19. MASP-1 and/or MASP-2 present an increased expression in patients with COVID-19 risk factors: diabetes, arterial hypertension and cardiovascular disease, chronic kidney disease, chronic obstructive pulmonary disease, and cerebrovascular disease. Based also on the positive results of COVID-19 patients with anti-MASP-2 antibody, we propose the use of MASPs as a possible biomarker of the progression of COVID-19 and the investigation of new treatment strategies taking into consideration the dual role of MASPs, including MASP inhibitors as promising therapeutic targets against COVID-19.

Molecular Dambusters: What Is Behind Hyperpermeability in Bradykinin-Mediated Angioedema?

In the last few decades, a substantial body of evidence underlined the pivotal role of bradykinin in certain types of angioedema. The formation and breakdown of bradykinin has been studied thoroughly; however, numerous questions remained open regarding the triggering, course, and termination of angioedema attacks. Recently, it became clear that vascular endothelial cells have an integrative role in the regulation of vessel permeability. Apart from bradykinin, a great number of factors of different origin, structure, and mechanism of action are capable of modifying the integrity of vascular endothelium, and thus, may participate in the regulation of angioedema formation. Our aim in this review is to describe the most important permeability factors and the molecular mechanisms how they act on endothelial cells. Based on endothelial cell function, we also attempt to explain some of the challenging findings regarding bradykinin-mediated angioedema, where the function of bradykinin itself cannot account for the pathophysiology. By deciphering the complex scenario of vascular permeability regulation and edema formation, we may gain better scientific tools to be able to predict and treat not only bradykinin-mediated but other types of angioedema as well.

Complement Activation in the Central Nervous System: A Biophysical Model for Immune Dysregulation in the Disease State

Complement, a feature of the innate immune system that targets pathogens for phagocytic clearance and promotes inflammation, is tightly regulated to prevent damage to host tissue. This regulation is paramount in the central nervous system (CNS) since complement proteins degrade neuronal synapses during development, homeostasis, and neurodegeneration. We propose that dysregulated complement, particularly C1 or C3b, may errantly target synapses for immune-mediated clearance, therefore highlighting regulatory failure as a major potential mediator of neurological disease. First, we explore the mechanics of molecular neuroimmune relationships for the regulatory proteins: Complement Receptor 1, C1-Inhibitor, Factor H, and the CUB-sushi multiple domain family. We propose that biophysical and chemical principles offer clues for understanding mechanisms of dysregulation. Second, we describe anticipated effects to CNS disease processes (particularly Alzheimer's Disease) and nest our ideas within existing basic science, clinical, and epidemiological findings. Finally, we illustrate how the concepts presented within this manuscript provoke new ways of approaching age-old neurodegenerative processes. Every component of this model is testable by straightforward experimentation and highlights the untapped potential of complement dysregulation as a driver of CNS disease. This includes a putative role for complement-based neurotherapeutic agents and companion biomarkers.

Pathways of Neutrophil Granulocyte Activation in Hereditary Angioedema with C1 Inhibitor Deficiency

Hereditary angioedema (HAE) with C1-inhibitor deficiency belongs to bradykinin-mediated angioedemas. It is characterized by recurrent subcutaneous and/or submucosal swelling episodes (HAE attacks) and erythema marginatum skin rash as a pre-attack (prodromal) phase. HAE attacks were shown to be accompanied by peripheral blood neutrophilia. We aimed to find molecular mechanisms that may explain the distinct role of neutrophil granulocytes in HAE. Plasma levels of blood cells and factors related to neutrophil activation (cytokines, chemokines, chemotactic factors, enzymes, and neutrophil extracellular trap) were measured in plasma samples obtained from patients during symptom-free periods (n = 77), during prodromal phase (n = 8) and attacks (n = 14), during a spontaneously resolved attack (n = 1), and in healthy controls (n = 79). Higher counts of white blood cells, lymphocytes, and neutrophil granulocytes were found in symptom-free patients compared with controls; these cell counts were elevated further during HAE attacks. The level of chemokine (C–C motif) ligand 5, monocyte chemoattractant protein-1, and myeloperoxidase were also higher in the symptom-free patients than in the controls. Levels of monocyte chemoattractant protein-1, leukotriene B4, neutrophil elastase, and myeloperoxidase were elevated during attacks. During erythema marginatum, white blood cells and monocyte count and levels of interleukin 8 were elevated compared with symptom-free period. Similar changes were detected during the attack follow-up. We conclude that the activation of NGs in symptom-free periods and a further increase observed during attacks suggests that NGs may be involved in the pathomechanism of HAE with C1-INH deficiency.