The alternative complement pathway is longitudinally associated with adverse cardiovascular outcomes

Adipsin in the pathogenesis of cardiovascular diseases

Adipsin is an adipokine predominantly synthesized in adipose tissues and released into circulation. It is also known as complement factor-D (CFD), acting as the rate-limiting factor in the alternative complement pathway and exerting essential functions on the activation of complement system. The deficiency of CFD in humans is a very rare condition. However, complement overactivation has been implicated in the etiology of numerous disorders, including cardiovascular disease (CVD). Increased circulating level of adipsin has been reported to promote vascular derangements, systemic inflammation, and endothelial dysfunction. Prospective and case-control studies showed that this adipokine is directly associated with all-cause death and rehospitalization in patients with coronary artery disease. Adipsin has also been implicated in pulmonary arterial hypertension, abdominal aortic aneurysm, pre-eclampsia, and type-2 diabetes which is a major risk factor for CVD. Importantly, serum adipsin has been recognized as a unique prognostic marker for assessing cardiovascular diseases. At present, there is paucity of experimental evidence about the precise role of adipsin in the etiology of CVD. However, this mini review provides some insight on the contribution of adipsin in the pathogenesis of CVD and highlights its role on endothelial, smooth muscle and immune cells that mediate cardiovascular functions.

Serum proteomic identification and validation of two novel atherosclerotic aortic aneurysm biomarkers, profilin 1 and complement factor D

BACKGROUND

Effective diagnostic biomarkers for aortic aneurysm (AA) that are detectable in blood tests are required because early detection and rupture risk assessment of AA can provide insights into medical therapy and preventive treatments. However, known biomarkers for AA lack specificity and reliability for clinical diagnosis.

METHODS

We performed proteome analysis of serum samples from patients with atherosclerotic thoracic AA (TAA) and healthy control (HC) subjects to identify diagnostic biomarkers for AA. Serum samples were separated into low-density lipoprotein, high-density lipoprotein, and protein fractions, and the major proteins were depleted. From the proteins identified in the three fractions, we narrowed down biomarker candidates to proteins uniformly altered in all fractions between patients with TAA and HC subjects and evaluated their capability to discriminate patients with TAA and those with abdominal AA (AAA) from HC subjects using receiver operating characteristic (ROC) analysis. For the clinical validation, serum concentrations of biomarker candidates were measured in patients with TAA and AAA registered in the biobank of the same institute, and their capability for the diagnosis was evaluated.

RESULTS

Profilin 1 (PFN1) and complement factor D (CFD) showed the most contrasting profiles in all three fractions between patients with TAA and HC subjects and were selected as biomarker candidates. The PFN1 concentration decreased, whereas the CFD concentration increased in the sera of patients with TAA and AAA when compared with those of HC subjects. The ROC analysis showed that these proteins could discriminate patients with TAA and AAA from HC subjects. In the validation study, these candidates showed significant concentration differences between patients with TAA or AAA and controls. PFN1 and CFD showed sufficient area under the curve (AUC) in the ROC analysis, and their combination further increased the AUC. The serum concentrations of PFN1 and CFD also showed significant differences between patients with aortic dissection and controls in the validation study.

CONCLUSION

PFN1 and CFD are potential diagnostic biomarkers for TAA and AAA and measurable in blood samples; their diagnostic performance can be augmented by their combination. These biomarkers may facilitate the development of diagnostic systems to identify patients with AA.

Plasma factor D is cross-sectionally associated with low-grade inflammation, endothelial dysfunction and cardiovascular disease: The Maastricht study

BACKGROUND AND AIMS

The complement system, particularly the alternative complement pathway, may contribute to vascular damage and development of cardiovascular disease (CVD). We investigated the association of factor D, the rate-limiting protease in alternative pathway activation, with adverse cardiovascular outcomes.

METHODS

In 2947 participants (50.6% men, 59.9 ± 8.2 years, 26.5% type 2 diabetes [T2D], oversampled) we measured markers of low-grade inflammation (LGI, composite score, in SD) and, endothelial dysfunction (ED, composite score, in SD), carotid intima-media thickness (cIMT, μm), ankle-brachial index (ABI), CVD (yes/no) and plasma concentrations of factor D (in SD). Associations were estimated using multiple linear and logistic regression, adjusting for demographic, lifestyle, and dietary factors.

RESULTS

Factor D (per SD) significantly associated with LGI (0.171 SD [0.137; 0.205]), ED (0.158 SD [0.123; 0.194]) and CVD (OR 1.15 [1.04; 1.27]) but not significantly with cIMT (-6.62 μm [-13.51; 0.27]) or ABI (-0.003 [-0.007; 0.001]). Interaction analyses show that factor D more strongly associated with ED in non-diabetes (0.237 SD [0.189; 0.285] than in T2D (0.095 SD [0.034; 0.157]), pinteraction <0.05. These results were largely corroborated by additional analyses with C3 and C3a. In contrast, factor D inversely associated with cIMT in non-diabetes (-13.37 μm [-21.84; -4.90]), but not in T2D (4.49 [-7.91; 16.89]), pinteraction <0.05.

CONCLUSIONS

Plasma factor D is independently associated with LGI, ED, and prevalent CVD but not with ABI or cIMT. Hence, greater plasma factor D concentration in CVD may potentially induce complement activation which, in turn, might contribute to further disease progression via a process that may involve inflammation and endothelial dysfunction but was not directly related to atherosclerosis or arterial injury. The observation that, in participants without diabetes, factor D associated with worse ED but smaller cIMT warrants further investigation.

Alternative pathway activation in pregnancy, a measured amount "complements" a successful pregnancy, too much results in adverse events

During pregnancy, the maternal host must adapt in order to enable growth of the fetus. These changes affect all organ systems and are designed both to protect the fetus and to minimize risk to the mother. One of the most prominent adaptations involves the immune system. The semi-allogenic fetoplacental unit has non-self components and must be protected against attack from the host. This requires both attenuation of adaptive immunity and protection from innate immune defense mechanisms. One of the key innate immune players is complement, and it is important that the fetoplacental unit is not identified as non-self and subjected to complement attack. Adaptation of the complement response must, however, be managed in such a way that maternal protection against infection is not compromised. As the complement system also plays a significant facilitating role in many of the stages of a normal pregnancy, it is also important that any necessary adaptation to accommodate the semi-allogenic aspects of the fetoplacental unit does not compromise this. In this review, both the physiological role of the alternative pathway of complement in facilitating a normal pregnancy, and its detrimental participation in pregnancy-specific disorders, are discussed.

Complement factors D and C3 cross-sectionally associate with arterial stiffness, but not independently of metabolic risk factors: The Maastricht Study

BACKGROUND

Arterial stiffness predicts cardiovascular outcomes. The complement system, particularly the alternative complement pathway, has been implicated in cardiovascular diseases. We herein investigated the associations of factor D, the rate-limiting protease of the alternative pathway, and C3, the central complement component, with arterial stiffness.

METHODS

In 3019 population-based participants (51.9% men, 60.1 ± 8.2 years, 27.7% type 2 diabetes [T2D], oversampled]), we measured carotid-femoral pulse wave velocity (cfPWV), carotid distensibility coefficient (DC) and carotid Young's elastic modulus (YEM), and plasma concentrations of factors D and C3. We conducted multiple linear regression to investigate the association of factors D and C3 (main independent variables, standardized) with cfPWV (primary outcome) and DC and YEM (secondary outcomes), adjusted for potential confounders.

RESULTS

Per SD higher factors D and C3, cfPWV was 0.41 m/s [95% confidence interval: 0.34; 0.49] and 0.33 m/s [0.25; 0.41] greater, respectively. These associations were substantially attenuated when adjusted for age, sex, education, mean arterial pressure, and heart rate (0.08 m/s [0.02; 0.15] and 0.11 m/s [0.05; 0.18], respectively), and were not significant when additionally adjusted for T2D, waist circumference and additional cardiovascular risk factors (0.06 m/s [-0.01; 0.13] and 0.01 m/s [-0.06; 0.09], respectively). Results were comparable for carotid YEM and DC. In persons with T2D, but not in those without, the association between factors D and cfPWV was significant in the fully adjusted model (0.14 m/s, [0.01; 0.27], P  = 0.038, Pinteraction  < 0.05).

CONCLUSION

The strong association of plasma factors D and C3 with arterial stiffness in this population-based cohort was not independent of T2D and other metabolic risk factors. Our data suggest that a possible causal pathway starting from alternative complement activation may via hypertension and T2D contribute to greater arterial stiffness.

A randomized diet-induced weight-loss intervention reduces plasma complement C3: Possible implication for endothelial dysfunction

OBJECTIVE

Complement C3 and other components of the alternative pathway are higher in individuals with obesity. Moreover, C3 has been identified as a risk factor for cardiovascular disease. This study investigated whether, and how, a weight-loss intervention reduced plasma C3, activated C3 (C3a), and factor D and explored potential biological effects of such a reduction.

METHODS

The study measured plasma C3, C3a, and factor D by ELISA and measured visceral adipose tissue, subcutaneous adipose tissue, and intrahepatic lipid by magnetic resonance imaging in lean men (n = 25) and men with abdominal obesity (n = 52). The men with obesity were randomized to habitual diet or an 8-week dietary weight-loss intervention.

RESULTS

The intervention significantly reduced C3 (-0.15 g/L [95% CI: -0.23 to -0.07]), but not C3a or factor D. The C3 reduction was mainly explained by reduction in visceral adipose tissue but not subcutaneous adipose tissue or intrahepatic lipid. This reduction in C3 explained a part of the weight-loss-induced improvement of markers of endothelial dysfunction, particularly the reduction in soluble endothelial selectin and soluble intercellular adhesion molecule.

CONCLUSIONS

Diet-induced weight loss in men with abdominal obesity could be a way to lower plasma C3 and thereby improve endothelial dysfunction. C3 reduction may be part of the mechanism via which diet-induced weight loss could ameliorate the risk of cardiovascular disease in men with abdominal obesity.

Diagnostic circulating biomarkers to detect vision-threatening diabetic retinopathy: Potential screening tool of the future?

With the increasing prevalence of diabetes in developing and developed countries, the socio-economic burden of diabetic retinopathy (DR), the leading complication of diabetes, is growing. Diabetic retinopathy (DR) is currently one of the leading causes of blindness in working-age adults worldwide. Robust methodologies exist to detect and monitor DR; however, these rely on specialist imaging techniques and qualified practitioners. This makes detecting and monitoring DR expensive and time-consuming, which is particularly problematic in developing countries where many patients will be remote and have little contact with specialist medical centres. Diabetic retinopathy (DR) is largely asymptomatic until late in the pathology. Therefore, early identification and stratification of vision-threatening DR (VTDR) is highly desirable and will ameliorate the global impact of this disease. A simple, reliable and more cost-effective test would greatly assist in decreasing the burden of DR around the world. Here, we evaluate and review data on circulating protein biomarkers, which have been verified in the context of DR. We also discuss the challenges and developments necessary to translate these promising data into clinically useful assays, to detect VTDR, and their potential integration into simple point-of-care testing devices.

The role of properdin and Factor H in disease

The complement system consists of three pathways (alternative, classical, and lectin) that play a fundamental role in immunity and homeostasis. The multifunctional role of the complement system includes direct lysis of pathogens, tagging pathogens for phagocytosis, promotion of inflammatory responses to control infection, regulation of adaptive cellular immune responses, and removal of apoptotic/dead cells and immune complexes from circulation. A tight regulation of the complement system is essential to avoid unwanted complement-mediated damage to the host. This regulation is ensured by a set of proteins called complement regulatory proteins. Deficiencies or malfunction of these regulatory proteins may lead to pro-thrombotic hematological diseases, renal and ocular diseases, and autoimmune diseases, among others. This review focuses on the importance of two complement regulatory proteins of the alternative pathway, Factor H and properdin, and their role in human diseases with an emphasis on: (a) characterizing the main mechanism of action of Factor H and properdin in regulating the complement system and protecting the host from complement-mediated attack, (b) describing the dysregulation of the alternative pathway as a result of deficiencies, or mutations, in Factor H and properdin, (c) outlining the clinical findings, management and treatment of diseases associated with mutations and deficiencies in Factor H, and (d) defining the unwanted and inadequate functioning of properdin in disease, through a discussion of various experimental research findings utilizing in vitro, mouse and human models.

Transcriptomic and Lipidomic Mapping of Macrophages in the Hub of Chronic Beta-Adrenergic-Stimulation Unravels Hypertrophy-, Proliferation-, and Lipid Metabolism-Related Genes as Novel Potential Markers of Early Hypertrophy or Heart Failure

Sympathetic nervous system overdrive with chronic release of catecholamines is the most important neurohormonal mechanism activated to maintain cardiac output in response to heart stress. Beta-adrenergic signaling behaves first as a compensatory pathway improving cardiac contractility and maladaptive remodeling but becomes dysfunctional leading to pathological hypertrophy and heart failure (HF). Cardiac remodeling is a complex inflammatory syndrome where macrophages play a determinant role. This study aimed at characterizing the temporal transcriptomic evolution of cardiac macrophages in mice subjected to beta-adrenergic-stimulation using RNA sequencing. Owing to a comprehensive bibliographic analysis and complementary lipidomic experiments, this study deciphers typical gene profiles in early compensated hypertrophy (ECH) versus late dilated remodeling related to HF. We uncover cardiac hypertrophy- and proliferation-related transcription programs typical of ECH or HF macrophages and identify lipid metabolism-associated and Na⁺ or K⁺ channel-related genes as markers of ECH and HF macrophages, respectively. In addition, our results substantiate the key time-dependent role of inflammatory, metabolic, and functional gene regulation in macrophages during beta-adrenergic dependent remodeling. This study provides important and novel knowledge to better understand the prevalent key role of resident macrophages in response to chronically activated beta-adrenergic signaling, an effective diagnostic and therapeutic target in failing hearts.

The Alternative Complement Pathway Is Activated Without a Corresponding Terminal Pathway Activation in Patients With Heart Failure

Objective

Dysregulation of the complement system has been described in patients with heart failure (HF). However, data on the alternative pathway are scarce and it is unknown if levels of factor B (FB) and the C3 convertase C3bBbP are elevated in these patients. We hypothesized that plasma levels of FB and C3bBbP would be associated with disease severity and survival in patients with HF.

Methods

We analyzed plasma levels of FB, C3bBbP, and terminal C5b-9 complement complex (TCC) in 343 HF patients and 27 healthy controls.

Results

Compared with controls, patients with HF had elevated levels of circulating FB (1.6-fold, p < 0.001) and C3bBbP (1.3-fold, p < 0.001). In contrast, TCC, reflecting the terminal pathway, was not significantly increased (p = 0.15 vs controls). FB was associated with NT-proBNP, troponin, eGFR, and i.e., C-reactive protein. FB, C3bBbP and TCC were not associated with mortality in HF during a mean follow up of 4.3 years.

Conclusion

Our findings suggest that in patients with HF, the alternative pathway is activated. However, this is not accompanied by activation of the terminal pathway.

Hypoglycemia-induced changes in complement pathways in type 2 diabetes

Background and aims

An association between hypoglycaemia and adverse cardiovascular events has been suggested from longitudinal and retrospective cohort studies. The complement pathway proteins in hypoglycemia are not well studied. Here, we hypothesized that these circulating proteins would be elevated in response to hypoglycemia in type 2 diabetes (T2D) through the inflammatory response.

Methods

A prospective, parallel study in T2D (n = 23) and controls (n = 23). Subjects underwent insulin-induced hypoglycemia with blood sampling at baseline, hypoglycemia and post-hypoglycemia; SOMAscan proteomic analysis of complement pathway-related proteins, cytokines and inflammatory proteins was undertaken.

Results

At baseline: Complement C2 (p < 0.05) and Factor B (p < 0.05) were elevated in T2D. At hypoglycemia: Complement C2 (p < 0.05) and Factor B (p < 0.01) remained elevated, whilst Factor I became elevated (p < 0.05) in T2D; Complement C4b became elevated in controls (p < 0.05). In the post-hypoglycemia follow up period, Complement C2, Factor B and Factor I remained elevated in T2D; in addition, Factor D, Factor H and mannose-binding protein C showed elevations in T2D, whilst properdin, complement C3b, Factor H-related protein 5, complement C1q and decay-accelerating factor (DAF) showed elevations in controls. Granger causality analysis showed that inflammatory proteins appeared to drive complement protein changes in T2D; conversely, in controls, complement proteins drove inflammatory protein changes.

Conclusions

Baseline elevations in C2 and Factor B indicate upregulation of the complement pathway in T2D. Changes in complement pathway-related protein levels in response to hypoglycemia suggest both intrinsic and alternative pathway activation at 2-h that appears driven by the underlying inflammation in T2D and could contribute to a cardiovascular event.ClinicalTrials.gov NCT03102801. Date of registration April 6, 2017, retrospectively registered. https://clinicaltrials.gov/ct2/show/NCT03102801?term=NCT03102801&draw=2&rank=1.

Association between serum adipsin and plaque vulnerability determined by optical coherence tomography in patients with coronary artery disease

Background

Early identification of vulnerable plaques is important for patients with coronary artery disease (CAD) to reduce acute coronary events and improve their prognosis. We sought to examine the relationship between adipsin, an adipokine secreted from adipocytes, and plaque vulnerability in CAD patients.

Methods

A total of 103 plaques from 99 consecutive patients who underwent coronary angiography were assessed by optical coherence tomography. The serum level of adipsin was measured using enzyme-linked immunosorbent assay (ELISA). The accuracy of adipsin for detecting thin-cap fibroatheroma (TCFA) was determined by the area under the receiver operating characteristic curve (AUC).

Results

Of the 99 patients, 49 were classified into the low adipsin group and 50 into the high adipsin group according to the median level of serum adipsin (2.43 µg/mL). The plaques from the high adipsin group exhibited a greater lipid index (2,700.0 vs. 1,975.9° × mm, P=0.015) and an increased proportion of TCFAs (41.2% vs. 21.2%, P=0.028) compared with the low adipsin group. Serum adipsin was found to be negatively correlated with fibrous cap thickness (ρ=−0.322, P=0.002), while it was positively correlated with average lipid arc (ρ=0.253, P=0.015), maximum lipid arc (ρ=0.211, P=0.044), lipid core length (ρ=0.241, P=0.021), lipid index (ρ=0.335, P=0.001), and vulnerability score (ρ=0.254, P=0.014). Furthermore, adipsin had a significant association with TCFAs (OR: 1.290, 95% CI: 1.048–1.589, P=0.016) in the multivariate analysis, while having a moderate diagnostic accuracy for TCFAs (AUC: 0.710, 95% CI: 0.602–0.817, P<0.001).

Conclusions

Our findings suggest that serum adipsin is significantly and positively correlated with the incidence of TCFAs. The application of adipsin as a biomarker may offer improvement in the diagnosis of vulnerable plaques and clinical benefits for CAD patients.

C3 and alternative pathway components are associated with an adverse lipoprotein subclass profile: The CODAM study

BACKGROUND

Plasma lipoproteins contain heterogeneous subclasses. Previous studies on the associations of the complement system with lipids and lipoproteins are mainly limited to the major lipid classes, and associations of complement with lipoprotein subclass characteristics remain unknown.

OBJECTIVE

We investigated the associations of C3 and other components of the alternative complement pathway with plasma lipoprotein subclass profile.

METHODS

Plasma complement concentrations (complement component 3 [C3], properdin, factor H, factor D, MASP-3, C3a, Bb), and lipoprotein subclass profile (as measured by nuclear magnetic resonance spectroscopy) were obtained in 523 participants (59.6 ± 6.9 years, 60.8% men) of the Cohort on Diabetes and Atherosclerosis Maastricht (CODAM) study. Multiple linear regression was used to investigate the associations of C3 (primary determinant) and other alternative pathway components (secondary determinants) with characteristics (particle concentration and size [main outcomes], and lipid contents [secondary outcomes]) of 14 lipoprotein subclasses, ranging from extremely large VLDL to small HDL (all standardized [std] values).

RESULTS

Participants with higher C3 concentrations had more circulating VLDL (stdβs ranging from 0.27 to 0.36), IDL and LDL (stdβs ranging from 0.14 to 0.17), and small HDL (stdβ = 0.21). In contrast, they had fewer very large and large HDL particles (stdβs = -0.36). In persons with higher C3 concentrations, all lipoprotein subclasses were enriched in triglycerides. Similar but weaker associations were observed for properdin, factor H, factor D, and MASP-3, but not for C3a and Bb.

CONCLUSIONS

The alternative complement pathway, and most prominently C3, is associated with an adverse lipoprotein subclass profile that is characterized by more triglyceride-enriched lipoproteins but fewer large HDL.

Extrinsic and Intrinsic Responses in the Development and Progression of Atherosclerosis

Atherosclerosis is a multifactorial disease that is thought to be primarily inflammatory in origin. Given the contribution of inflammation to the development and progression of atherosclerosis, other conditions that are characterised by a dysregulated inflammatory response have also been proposed to play a role. The purpose of this review is to organise and present the various inflammatory processes that can affect atherosclerosis into two broad categories: extrinsic or host-independent and intrinsic or host-dependent. Within these two categories, we will discuss various processes that may contribute to the development and progression of atherosclerosis and the clinical studies describing these associations. Although the clinical trials investigating anti-inflammatory therapies have to date provided mixed results, further studies, particularly in conjunction with lipid-lowering and blood pressure lowering therapies should be considered.

The role of the complement factor B-arginase-polyamine molecular axis in uremia-induced cardiac remodeling in mice

The role of complement system in heart diseases is controversial. Besides, the mechanisms by which complement components participate in cardiac remodeling (CR) and heart failure during uremia are unclear. In this study, 5/6 nephrectomy was performed to adult mice to establish the uremic model and CR deteriorated over the course of uremia. Although complement pathways were not further activated over the course of the disease, soluble complement factor B (CFB) was upregulated at post-nephrectomy day 90 (PNx90) compared with PNx30. Further, CFB notably deteriorated CR in uremic mice but this effect was reversed by depletion of macrophages with liposomal clodronate. In vivo and in vitro CFB upregulated arginase 1 (ARG1) expression, increased ARG1 enzymatic activity, and stimulated the syntheses of ornithine, leading to polyamine overproduction in macrophages. Putrescine, an important polyamine, promoted cardiac fibroblast proliferation and collagen production, resulting in progressive CR. In vivo the inhibition of ARG1 activity with N^ω -hydroxyl-l-arginine remarkably improved the general survival rates, inhibited the infiltration of cardiac fibroblasts, and alleviated progression of CR in uremic mice. Taken together, the CFB-ARG1-putrescine axis is related to progression of CR and ARG1 hyperactivity in macrophages may provide a novel therapeutic target against the heart injury in uremia.

The endocrine function of adipose tissues in health and cardiometabolic disease

In addition to their role in glucose and lipid metabolism, adipocytes respond differentially to physiological cues or metabolic stress by releasing endocrine factors that regulate diverse processes, such as energy expenditure, appetite control, glucose homeostasis, insulin sensitivity, inflammation and tissue repair. Both energy-storing white adipocytes and thermogenic brown and beige adipocytes secrete hormones, which can be peptides (adipokines), lipids (lipokines) and exosomal microRNAs. Some of these factors have defined targets; for example, adiponectin and leptin signal through their respective receptors that are expressed in multiple organs. For other adipocyte hormones, receptors are more promiscuous or remain to be identified. Furthermore, many of these hormones are also produced by other organs and tissues, which makes defining the endocrine contribution of adipose tissues a challenge. In this Review, we discuss the functional role of adipose tissue-derived endocrine hormones for metabolic adaptations to the environment and we highlight how these factors contribute to the development of cardiometabolic diseases. We also cover how this knowledge can be translated into human therapies. In addition, we discuss recent findings that emphasize the endocrine role of white versus thermogenic adipocytes in conditions of health and disease.

Gene Expression Differences in Pediatric Lymphatic Malformations: Size Really Matters

Lymphatic malformations (LMs) are congenital vascular anomalies characterized by dilated and cystic lymphatic channels. They are subdivided into macrocystic and microcystic lesions based upon the predominant size of the cysts involved. However, significant differences in clinical characteristics, treatment outcomes, and prognosis between macrocytic and microcytic disease suggest variation in underlying biologic and genetic influences. Indirect differential expression analysis revealed that 426 genes are significantly different (p < 0.01) in a small sample of LM subtypes. Functional analyses on the differentially expressed gene sets showed that microcystic LM gene expression favors a prooncogenic profile with upregulation of MYC target genes and cell cycle proteins, whereas macrocystic expression demonstrates hypoxic events that lead to angiogenesis and cell proliferation. Therefore, microcystic and macrocystic LMs, although histologically and physiologically similar, may occur under the influence of vastly different biological pathways and mechanisms of action.

The role of properdin in complement-mediated renal diseases: a new player in complement-inhibiting therapy?

Properdin is known as the only positive regulator of the complement system. Properdin promotes the activity of this defense system by stabilizing its key enzymatic complexes: the complement alternative pathway (AP) convertases. Besides, some studies have indicated a role for properdin as an initiator of complement activity. Though the AP is a powerful activation route of the complement system, it is also involved in a wide variety of autoimmune and inflammatory diseases, many of which affect the kidneys. The role of properdin in regulating complement in health and disease has not received as much appraisal as the many negative AP regulators, such as factor H. Historically, properdin deficiency has been strongly associated with an increased risk for meningococcal disease. Yet only recently had studies begun to link properdin to other complement-related diseases, including renal diseases. In the light of the upcoming complement-inhibiting therapies, it is interesting whether properdin can be a therapeutic target to attenuate AP-mediated injury. A full understanding of the basic concepts of properdin biology is therefore needed. Here, we first provide an overview of the function of properdin in health and disease. Then, we explore its potential as a therapeutic target for the AP-associated renal diseases C3 glomerulopathy, atypical hemolytic uremic syndrome, and proteinuria-induced tubulointerstitial injury. Considering current knowledge, properdin-inhibiting therapy seems promising in certain cases. However, knowing the complexity of properdin's role in renal pathologies in vivo, further research is required to clarify the exact potential of properdin-targeted therapy in complement-mediated renal diseases.

Complement C3 and C4, but not their regulators or activated products, are associated with incident metabolic syndrome: the CODAM study

PURPOSE

We investigated the associations of components of the alternative (C3, C3a, Bb, factor D [FD], factor H [FH], properdin) and the classical complement pathway (C4, C1q, C1-inhibitor [C1-INH]) with prevalent and incident metabolic syndrome in a cohort with a moderately increased risk of cardiometabolic disease.

METHODS

The study cohort was comprised of 574 participants (61% men, age 59.6 ± 7.0 years) at baseline and 489 participants after 7-year follow-up. Multiple logistic regression analyses were done to investigate the associations of concentrations of baseline plasma complement (standardized values) with prevalent and incident (in those without metabolic syndrome at baseline, n = 189) metabolic syndrome.

RESULTS

C3 (odds ratio (OR) = 1.48 [95% confidence interval: 1.02; 2.14]) and C4 (OR = 1.95 [1.32; 2.88]), but none of the other complement components were associated with incident metabolic syndrome (n = 40 cases). Notably, in the cross-sectional analyses, we did observe higher levels of C3a (OR = 1.25 [1.03; 1.52]), FH (OR = 2.93 [2.24; 3.83]), and properdin (OR = 1.88 [1.50; 2.34]), in addition to C3 (OR = 3.60 [2.73; 4.75]) and C4 (OR = 1.39 [1.13; 1.69]), in those with the metabolic syndrome compared to those without, while no association was observed for FD, Bb, C1q, or C1-INH.

CONCLUSIONS

In the cross-sectional analyses, the effects sizes (standardized regression coefficients) for C3 and C4 were similar to those of (some of) the regulators and activators, yet only C3 and C4 were associated with incident disease. These findings suggest a role for C3 and C4, but not their regulators or activated products, in the development of the metabolic syndrome.

Endothelial Microparticles and Systemic Complement Activation in Patients With Chronic Kidney Disease

BACKGROUND

Endothelial microparticles are associated with chronic kidney disease (CKD) and complement activation. We hypothesized that the complement pathway is activated in patients with CKD via endothelial microparticles and that complement activation correlates with endothelial dysfunction in CKD.

METHODS AND RESULTS

We analyzed complement data of 30 healthy subjects, 30 patients with stage III/IV CKD, and 30 renal transplant recipients with stage III/IV CKD, evaluating the potential correlation of complement fragments with brachial artery flow-mediated dilation, Chronic Kidney Disease Epidemiology Collaboration glomerular filtration rate, and urinary albumin/creatinine ratio. Endothelial microparticles were characterized via proteomic analysis and compared between study groups. Complement fragment Ba was significantly increased in CKD and post-kidney transplant CKD. Plasma Ba levels correlated significantly with lower brachial artery flow-mediated dilation, lower Chronic Kidney Disease Epidemiology Collaboration glomerular filtration rate, and higher urinary albumin/creatinine ratio. Factor D levels were significantly higher in the plasma microparticles of patients with CKD versus healthy controls. Plasma microparticles isolated from patients with CKD and containing factor D activated the alternative pathway in vitro.

CONCLUSION

The alternative complement pathway is activated in CKD and correlates with endothelial dysfunction and markers of CKD. Future studies are needed to evaluate whether endothelial microparticles with increased factor D play a pathologic role in CKD-associated vascular disease.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT02230202.

Properdin: A multifaceted molecule involved in inflammation and diseases

Properdin, the widely known positive regulator of the alternative pathway (AP), has undergone significant investigation over the last decade to define its function in inflammation and disease, including its role in arthritis, asthma, and kidney and cardiovascular diseases. Properdin is a glycoprotein found in plasma that is mainly produced by leukocytes and can positively regulate AP activity by stabilizing C3 and C5 convertases and initiating the AP. Promotion of complement activity by properdin results in changes in the cellular microenvironment that contribute to innate and adaptive immune responses, including pro-inflammatory cytokine production, immune cell infiltration, antigen presenting cell maturation, and tissue damage. The use of properdin-deficient mouse models and neutralizing antibodies has contributed to the understanding of the mechanisms by which properdin contributes to promoting or preventing disease pathology. This review mainly focusses on the multifaceted roles of properdin in inflammation and diseases, and how understanding these roles is contributing to the development of new disease therapies.

Cafestol Inhibits Cyclic-Strain-Induced Interleukin-8, Intercellular Adhesion Molecule-1, and Monocyte Chemoattractant Protein-1 Production in Vascular Endothelial Cells

Moderate coffee consumption is inversely associated with cardiovascular disease mortality; however, mechanisms underlying this causal effect remain unclear. Cafestol, a diterpene found in coffee, has various properties, including an anti-inflammatory property. This study investigated the effect of cafestol on cyclic-strain-induced inflammatory molecule secretion in vascular endothelial cells. Cells were cultured under static or cyclic strain conditions, and the secretion of inflammatory molecules was determined using enzyme-linked immunosorbent assay. The effects of cafestol on mitogen-activated protein kinases (MAPK), heme oxygenase-1 (HO-1), and sirtuin 1 (Sirt1) signaling pathways were examined using Western blotting and specific inhibitors. Cafestol attenuated cyclic-strain-stimulated intercellular adhesion molecule-1 (ICAM-1), monocyte chemoattractant protein- (MCP-) 1, and interleukin- (IL-) 8 secretion. Cafestol inhibited the cyclic-strain-induced phosphorylation of extracellular signal-regulated kinase and p38 MAPK. By contrast, cafestol upregulated cyclic-strain-induced HO-1 and Sirt1 expression. The addition of zinc protoporphyrin IX, sirtinol, or Sirt1 silencing (transfected with Sirt1 siRNA) significantly attenuated cafestol-mediated modulatory effects on cyclic-strain-stimulated ICAM-1, MCP-1, and IL-8 secretion. This is the first study to report that cafestol inhibited cyclic-strain-induced inflammatory molecule secretion, possibly through the activation of HO-1 and Sirt1 in endothelial cells. The results provide valuable insights into molecular pathways that may contribute to the effects of cafestol.

Longitudinal associations of the alternative and terminal pathways of complement activation with adiposity: The CODAM study

OBJECTIVE

To investigate longitudinal associations of components of the alternative (C3, C3a, Bb, factor D [FD], factor H [FH], and properdin) and the terminal complement pathway (C5a, sC5b-9) with adiposity.

METHODS

A prospective human cohort study (n=574 at baseline, n=489 after 7 years follow-up) was analyzed. Generalized estimating equations were used to evaluate the longitudinal associations between complement components (standardized values) and adiposity (main outcome BMI [kg/m²]). Multiple linear regression models were used to investigate the associations between change in complement levels and change in BMI. Analyses were adjusted for age, sex, medication and lifestyle.

RESULTS

Over the 7-year period, baseline C3 was positively associated with BMI (β=1.72 [95% confidence interval (CI): 1.35; 2.09]). Positive associations were also observed for C3a (β=0.64 [0.31; 0.97]), FD (β=1.00 [0.59; 1.42]), FH (β=1.17 [0.82; 1.53]), and properdin (β=0.60 [0.28; 0.92]), but not for Bb, C5a or sC5b-9. Moreover, changes in C3 (β=0.52 [0.34; 0.71]) and FH (β=0.51 [0.32; 0.70]) were significantly associated with changes in BMI.

CONCLUSIONS

The complement system, particularly activation of the alternative pathway, may be involved in development of adiposity. Whether individual aspects of alternative pathway activation have a causal role in human obesity, remains to be investigated.

Evaluation of expression levels and mechanism of complement activation

The present study aimed to reveal the expression changes of complement system activation and complement activation product C3a receptor during acute myocardial infarction. Blood samples were collected from healthy individuals and from patients with coronary artery stenosis or acute myocardial infarction. The subjects received physical examination in hospital between January and July 2015 (n=5). Cytometric bead array was performed to measure the levels of complement system activation product anaphylatoxin C3a, C4a and C5a. Immunohistochemical investigations were performed in tissues of patients who underwent coronary artery bypass grafting between January and July 2015 to detect the expression of C3a receptor. The results of cytometric bead array showed that the content of complement activation products C3a, C4a and C5a in the plasma of patients with coronary artery stenosis and acute myocardial infarction were significantly higher than those of the control group (P<0.01). The results of immunoblotting suggested that the protein expression of C3a receptor in infarct tissues of patients with acute myocardial infarction was significantly higher than that of normal tissues adjacent to the infarcted area (P<0.05). There is complement system activation in patients with acute myocardial infarction. Additionally, the increase in the expression of complement C3a receptor in tissues of infarct area suggested that C3a-C3a receptor signaling pathway may be involved in the development of myocardial infarction.

Risks of newly onset hemorrhagic stroke in patients with neovascular age-related macular degeneration

PURPOSE

Age-related macular degeneration (AMD) is an eye disease causing blindness in the elderly. It shares many common possible pathogenic mechanisms with cardiovascular diseases. Many studies have discussed the association between AMD and stroke, but the results were inconsistent. Our aim was to determine the associations between neovascular AMD and the risk of stroke in the Taiwanese population.

METHODS

This is a retrospective cohort study. We used claims data from National Health Insurance Research Database. Patients aged more than 45 years without stroke, myocardial infarction, or any AMD were selected from 2001 to 2008 and followed until 2010. The index date was defined as the date of nAMD diagnosis (ICD-9 code, 362.52). The comparison group was patients without an nAMD diagnosis with age- and sex-matched to nAMD subjects at a ratio of up to 10 to 1. Kaplan-Meier survival analysis and Cox regression analysis were used. The incidence of stroke events (ICD-9 codes, 430-434) and their subtypes (hemorrhagic and ischemic) were primary outcomes. Secondary outcomes included acute myocardial infarction (AMI), composite AMI/stroke, and all-cause mortality.

RESULTS

Patients with nAMD had a higher risk of developing stroke, with an adjusted HR of 1.30 (95% CI, 1.01-1.68). A higher risk for hemorrhagic stroke (HR, 1.70, 95% CI, 1.03-2.83) was also found. No significant differences were observed in ischemic stroke, the composite of AMI/stroke, and all-cause mortality.

CONCLUSIONS

Patients with nAMD had a significantly higher risk of developing stroke, which was driven mainly by the increased risk of developing the hemorrhagic subtype.

Complement Factor B Is a Determinant of Both Metabolic and Cardiovascular Features of Metabolic Syndrome

CFB (complement factor B) is elevated in adipose tissue and serum from patients with type 2 diabetes mellitus and cardiovascular disease, but the causal relationship to disease pathogenesis is unclear. Cfb is also elevated in adipose tissue and serum of the spontaneously hypertensive rat, a well-characterized model of metabolic syndrome. To establish the role of CFB in metabolic syndrome, we knocked out the Cfb gene in the spontaneously hypertensive rat. Cfb-/- rats showed improved glucose tolerance and insulin sensitivity, redistribution of visceral to subcutaneous fat, increased adipocyte mitochondrial respiration, and marked changes in gene expression. Cfb-/- rats also had lower blood pressure, increased ejection fraction and fractional shortening, and reduced left ventricular mass. These changes in metabolism and gene expression, in adipose tissue and left ventricle, suggest new adipose tissue-intrinsic and blood pressure-independent mechanisms for insulin resistance and cardiac hypertrophy in the spontaneously hypertensive rat. In silico analysis of the human CFB locus revealed 2 cis-regulated expression quantitative trait loci for CFB expression significantly associated with visceral fat, circulating triglycerides and hypertension in genome-wide association studies. Together, these data demonstrate a key role for CFB in the development of spontaneously hypertensive rat metabolic syndrome phenotypes and of related traits in humans and indicate the potential for CFB as a novel target for treatment of cardiometabolic disease.

Polymorphisms in genes related to the complement system and antibody-mediated cardiac allograft rejection

BACKGROUND

Heart transplantation (HT) is a life-saving treatment for patients with end-stage heart failure. One of the main problems after HT is the humoral response termed antibody-mediated rejection (AMR). Complement activation plays a key role in AMR contributing to graft damage. The aim of this study was to analyze genetic variants in genes related to the complement pathways that could be associated with the development of AMR.

METHODS

Analysis of 51 genes related to the complement pathway was performed by next-generation sequencing in 46 HT recipients, 23 with and 23 without AMR. Statistical analysis was performed with SNPstats and R.

RESULTS

We identified 2 single nucleotide polymorphisms, 1 in the mannose-binding lectin 2 gene (p.Gly54Asp-MBL2) and 1 in the complement factor properdin gene (p.Asn428(p=)-CFP), that showed significant association with the absence and development of AMR, respectively. Moreover, the presence of the rare allele in p.Gly54Asp-MBL2 control patients correlated with an immunodeficiency of mannose-binding lectin (6.24 ng/ml vs 207.50 ng/ml, p < 0.01), whereas the presence of the rare allele p.Asn428(p=)-CFP in patients with AMR correlated with higher levels of properdin protein (14.65 μg/ml vs 10.77 μg/ml, p < 0.05).

CONCLUSIONS

AMR is a complex phenotype affected by many recipient factors. Variants in p.Gly54Asp-MBL2 and p.Asn428(p=)-CFP genes, encoding mannose-binding lectin 2 and properdin, may influence the risk of AMR.

Hypaphorine Attenuates Lipopolysaccharide-Induced Endothelial Inflammation via Regulation of TLR4 and PPAR-γ Dependent on PI3K/Akt/mTOR Signal Pathway

Endothelial lesion response to injurious stimuli is a necessary step for initiating inflammatory cascades in blood vessels. Hypaphorine (Hy) from different marine sources is shown to exhibit anti-inflammatory properties. However, the potential roles and possible molecular mechanisms of Hy in endothelial inflammation have yet to be fully clarified. We showed that Hy significantly inhibited the positive effects of lipopolysaccharide (LPS) on pro-inflammatory cytokines expressions, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), monocyte chemoattractant protein 1 (MCP-1) and vascular cellular adhesion molecule-1 (VCAM-1), as well as induction of the phosphorylation of Akt and mTOR in HMEC-1 cells. The downregulated peroxisome proliferator-activated receptor γ (PPAR-γ) and upregulated toll-like receptor 4 (TLR4) expressions in LPS-challenged endothelial cells were prevented by Hy. Inhibition of both PI3K and mTOR reversed LPS-stimulated increases in TLR4 expressions and decreases in PPAR-γ levels. Genetic silencing of TLR4 or PPAR-γ agonist pioglitazone obviously abrogated the levels of pro-inflammatory cytokines in LPS-treated HMEC-1 cells. These results suggest that Hy may exert anti-inflammatory actions through the regulation of TLR4 and PPAR-γ dependent on PI3K/Akt/mTOR signal pathways. Hy may be considered as a therapeutic agent that can potentially relieve or ameliorate endothelial inflammation-associated diseases.

The alternative complement pathway is dysregulated in patients with chronic heart failure

The complement system, an important arm of the innate immune system, is activated in heart failure (HF). We hypothesized that HF patients are characterized by an imbalance of alternative amplification loop components; including properdin and complement factor D and the alternative pathway inhibitor factor H. These components and the activation product, terminal complement complex (TCC), were measured in plasma from 188 HF patients and 67 age- and sex- matched healthy controls by enzyme immunoassay. Our main findings were: (i) Compared to controls, patients with HF had significantly increased levels of factor D and TCC, and decreased levels of properdin, particularly patients with advanced clinical disorder (i.e., NYHA functional class IV), (ii) Levels of factor D and properdin in HF patients were correlated with measures of systemic inflammation (i.e., C-reactive protein), neurohormonal deterioration (i.e., Nt-proBNP), cardiac function, and deteriorated diastolic function, (iii) Low levels of factor H and properdin were associated with adverse outcome in univariate analysis and for factor H, this was also seen in an adjusted model. Our results indicate that dysregulation of circulating components of the alternative pathway explain the increased degree of complement activation and is related to disease severity in HF patients.

Dysfunctional adipose tissue and low-grade inflammation in the management of the metabolic syndrome: current practices and future advances

The ongoing worldwide obesity epidemic makes the metabolic syndrome an increasingly important entity. In this review, we provide a short background on the metabolic syndrome, we discuss recent developments in the three main options that have been identified for intervention in the metabolic syndrome, i.e. lifestyle and surgical and pharmacological interventions, and we focus on different views in the literature and also include our own viewpoints on the metabolic syndrome. In addition, we discuss some emerging treatment targets for adipose tissue dysfunction and low-grade inflammation, i.e. activation of the inflammasome and the complement system, and consider some selected opportunities for intervention in these processes.