Elevated C1rC1sC1inh levels independently predict atherosclerotic coronary heart disease

Cytoprotective effects of C1s enzyme in macrophages in atherosclerosis mediated through the LRP5 and Wnt/β-catenin pathway

C1s enzyme (active C1s) is a subunit of the complement C1 complex that cleaves low-density lipoprotein receptor-related proteins 5 and 6, leading to Wnt/β-catenin pathway activation in some cell lines. Macrophages have two major functional polarization states (the classically activated M1 state and the alternatively activated M2 state) and play an essential role in atherosclerosis. An increasing amount of evidence suggests that canonical Wnt signaling is related to macrophage polarization. In this study, we explored the cytoprotective effects of C1s enzyme in macrophages. The results show that C1s enzyme activates canonical Wnt signaling in macrophages, exacerbates macrophage M2 polarization, and inhibits M1 polarization. Moreover, C1s enzyme reduces foam cell formation and simultaneously enhances efferocytosis. This study reveals a novel function of C1s enzyme in macrophages in the context of atherosclerosis.

Free complement and complement containing extracellular vesicles as potential biomarkers for neuroinflammatory and neurodegenerative disorders

The complement system is implicated in a broad range of neuroinflammatory disorders such as Alzheimer's disease (AD) and multiple sclerosis (MS). Consequently, measuring complement levels in biofluids could serve as a potential biomarker for these diseases. Indeed, complement levels are shown to be altered in patients compared to controls, and some studies reported a correlation between the level of free complement in biofluids and disease progression, severity or the response to therapeutics. Overall, they are not (yet) suitable as a diagnostic tool due to heterogeneity of reported results. Moreover, measurement of free complement proteins has the disadvantage that information on their origin is lost, which might be of value in a multi-parameter approach for disease prediction and stratification. In light of this, extracellular vesicles (EVs) could provide a platform to improve the diagnostic power of complement proteins. EVs are nanosized double membrane particles that are secreted by essentially every cell type and resemble the (status of the) cell of origin. Interestingly, EVs can contain complement proteins, while the cellular origin can still be determined by the presence of EV surface markers. In this review, we summarize the current knowledge and future opportunities on the use of free and EV-associated complement proteins as biomarkers for neuroinflammatory and neurodegenerative disorders.

Proteomic analysis of extracellular vesicles enriched serum associated with future ischemic stroke

Identifying new biomarkers beyond the established risk factors that make it possible to predict and prevent ischemic stroke has great significance. Extracellular vesicles are powerful cell‒cell messengers, containing disease-specific biomolecules, which makes them powerful diagnostic candidates. Therefore, this study aimed to identify proteins derived from extracellular vesicles enriched serum related to future ischemic stroke events, using a proteomic method. Of Japanese subjects who voluntarily participated in health checkups at our institute a number of times, 10 subjects (6 males and 4 females, age: 64.2 ± 3.9 years) who developed symptomatic ischemic stroke (7.3 ± 4.4 years’ follow-up) and 10 age‒sex matched controls without brain lesions (6.7 ± 2.8 years’ follow-up) were investigated. Extracellular vesicles enriched fractions were derived from serum collected at the baseline visit. Differentially expressed proteins were evaluated using isobaric tagging for relative and absolute protein quantification (iTRAQ)-based proteomic analysis. Of the 29 proteins identified, alpha-2-macroglobulin, complement C1q subcomponent subunit B, complement C1r subcomponent, and histidine-rich glycoprotein were significantly upregulated (2.21-, 2.15-, 2.24-, and 2.16-fold, respectively) in subjects with future ischemic stroke, as compared with controls. Our study supports the concept of serum-derived extracellular vesicles enriched fractions as biomarkers for new-onset stroke. These proteins may be useful for prediction or for targeted therapy.

Serum Complement C1q Activity Is Associated With Obstructive Coronary Artery Disease

Background: Complement C1q plays a dual role in the atherosclerosis. Previous studies showed inconsistent results about the association of serum C1q levels and coronary artery disease (CAD). Here, we explored the associations of serum C1q activity with CAD, coronary stenosis severity, cardiovascular biomarkers, and 1-year restenosis after coronary artery revascularization.

Methods: We enrolled 956 CAD patients and 677 controls to evaluate the associations of serum complement C1q activity to the presence and severity of obstructive CAD and non-obstructive CAD. Serum C1q activity and the concentrations of laboratory markers were measured in all subjects. All the data were analyzed using SPSS22.0 software.

Results: Serum C1q activity in Obstructive CAD and Non-Obstructive CAD groups was significantly higher than the control group (195.52 ± 48.31 kU/L and 195.42 ± 51.25 kU/L vs. 183.44 ± 31.75 kU/L, P < 0.05). Greater C1q activity was significantly correlated with higher total cholesterol (TC) and triglyceride (TG) levels. C1q activity was associated with an increased Odds Ratio (OR) of CAD (OR = 1.322, 95% CI 1.168–1.496, P < 0.05) and 1-year restenosis after revascularization (the highest OR = 3.544, 95% CI 1.089–12.702, P < 0.05). Complement C1q activity was not correlated with Gensini score in the Obstructive CAD group after adjustment for confounders. C1q activity has low value in predicting the incidence of CAD.

Conclusion: Serum complement C1q activity is associated with obstructive CAD.

The alternative complement pathway is longitudinally associated with adverse cardiovascular outcomes

The alternative pathway of complement activation is highly reactive and can be activated spontaneously in the vasculature. Activation may contribute to vascular damage and development of cardiovascular disease (CVD). We aimed to investigate functional components of the alternative pathway in cardiovascular risk. We studied 573 individuals who were followed-up for seven years. At baseline, we measured the enhancer properdin; the rate-limiting protease factor D (FD); and a marker of systemic activation, Bb. Using generalised estimating equations, we investigated their longitudinal associations with cardiovascular events (CVE, N=89), CVD (N=159), low-grade inflammation (LGI), endothelial dysfunction (ED) and carotid intima-media thickness (cIMT). Furthermore, we investigated associations with incident CVE (N=39) and CVD (N=73) in 342 participants free of CVD at baseline. CVE included myocardial infarction, stroke, cardiac angioplasty and/or cardiac bypass. CVD additionally included ischaemia on an electrocardiogram and/or ankle-brachial index < 0.9. In adjusted analyses, properdin was positively associated with CVE (per 1SD, longitudinal OR=1.36 [1.07; 1.74], OR for incident CVE=1.53 [1.06; 2.20]), but not with CVD. Properdin was also positively associated with ED (β=0.13 [95 %CI 0.06; 0.20]), but not with LGI or cIMT. FD and Bb were positively associated with LGI (per 1SD, FD: β=0.21 [0.12; 0.29], Bb: β=0.14 [0.07; 0.21]), and ED (FD: β=0.20 [0.11; 0.29], Bb: β=0.10 [0.03; 0.18]), but not with cIMT, CVE or CVD. Taken together, this suggests that the alternative complement pathway contributes to processes of vascular damage, and that in particular a high potential to enhance alternative pathway activation may promote unfavourable cardiovascular outcomes in humans.

Supplementary Material to this article is available online at www.thrombosis-online.com.

Association of Low Ficolin-Lectin Pathway Parameters with Cardiac Syndrome X

In patients with typical angina pectoris, inducible myocardial ischaemia and macroscopically normal coronaries (cardiac syndrome X (CSX)), a significantly elevated plasma level of terminal complement complex (TCC), the common end product of complement activation, has been observed without accompanying activation of the classical or the alternative pathways. Therefore, our aim was to clarify the role of the ficolin-lectin pathway in CSX. Eighteen patients with CSX, 37 stable angina patients with significant coronary stenosis (CHD) and 54 healthy volunteers (HC) were enrolled. Serum levels of ficolin-2 and ficolin-3, ficolin-3/MASP-2 complex and ficolin-3-mediated TCC deposition (FCN3-TCC) were determined. Plasma level of TCC was significantly higher in the CSX than in the HC or CHD group (5.45 versus 1.30 versus 2.04 AU/ml, P < 0.001). Serum levels of ficolin-2 and ficolin-3 were significantly lower in the CSX compared to the HC or CHD group (3.60 versus 5.80 or 5.20 μg/ml, P < 0.05; 17.80 versus 24.10 or 26.80 μg/ml, P < 0.05). The ficolin-3/MASP-2 complex was significantly lower in the CSX group compared to the HC group (92.90 versus 144.90 AU/ml, P = 0.006). FCN3-TCC deposition was significantly lower in the CSX group compared to the HC and CHD groups (67.8% versus 143.3% or 159.7%, P < 0.05). In the CSX group, a significant correlation was found between TCC and FCN3-TCC level (r = 0.507, P = 0.032) and between ficolin-3/MASP-2 complex level and FCN3-TCC deposition (r = 0.651, P = 0.003). In conclusion, in patients with typical angina and myocardial ischaemia despite macroscopically normal coronary arteries, low levels of several lectin pathway parameters were observed, indicating complement activation and consumption. Complement activation through the ficolin-lectin pathway might play a role in the complex pathomechanism of CSX.

A vital role for complement in heart disease

Heart diseases are common and significant contributors to worldwide mortality and morbidity. During recent years complement mediated inflammation has been shown to be an important player in a variety of heart diseases. Despite some negative results from clinical trials using complement inhibitors, emerging evidence points to an association between the complement system and heart diseases. Thus, complement seems to be important in coronary heart disease as well as in heart failure, where several studies underscore the prognostic importance of complement activation. Furthermore, patients with atrial fibrillation often share risk factors both with coronary heart disease and heart failure, and there is some evidence implicating complement activation in atrial fibrillation. Moreover, Chagas heart disease, a protozoal infection, is an important cause of heart failure in Latin America, and the complement system is crucial for the protozoa-host interaction. Thus, complement activation appears to be involved in the pathophysiology of a diverse range of cardiac conditions. Determination of the exact role of complement in the various heart diseases will hopefully help to identify patients that might benefit from therapeutic complement intervention.

The complement system in human cardiometabolic disease

The complement system has been implicated in obesity, fatty liver, diabetes and cardiovascular disease (CVD). Complement factors are produced in adipose tissue and appear to be involved in adipose tissue metabolism and local inflammation. Thereby complement links adipose tissue inflammation to systemic metabolic derangements, such as low-grade inflammation, insulin resistance and dyslipidaemia. Furthermore, complement has been implicated in pathophysiological mechanisms of diet- and alcohol induced liver damage, hyperglycaemia, endothelial dysfunction, atherosclerosis and fibrinolysis. In this review, we summarize current evidence on the role of the complement system in several processes of human cardiometabolic disease. C3 is the central component in complement activation, and has most widely been studied in humans. C3 concentrations are associated with insulin resistance, liver dysfunction, risk of the metabolic syndrome, type 2 diabetes and CVD. C3 can be activated by the classical, the lectin and the alternative pathway of complement activation; and downstream activation of C3 activates the terminal pathway. Complement may also be activated via extrinsic proteases of the coagulation, fibrinolysis and the kinin systems. Studies on the different complement activation pathways in human cardiometabolic disease are limited, but available evidence suggests that they may have distinct roles in processes underlying cardiometabolic disease. The lectin pathway appeared beneficial in some studies on type 2 diabetes and CVD, while factors of the classical and the alternative pathway were related to unfavourable cardiometabolic traits. The terminal complement pathway was also implicated in insulin resistance and liver disease, and appears to have a prominent role in acute and advanced CVD. The available human data suggest a complex and potentially causal role for the complement system in human cardiometabolic disease. Further, preferably longitudinal studies are needed to disentangle which aspects of the complement system and complement activation affect the different processes in human cardiometabolic disease.