Role of complement in the pathomechanism of atherosclerotic vascular diseases

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.

Determination of the optimal concentration and duration of C5aR antagonist application in an inflammatory model of human dental pulp cells

Deep tooth decay approaching the pulp may develop into pulpitis; to prevent this, pulp cells need to balance the rapid immune response to avoid rapid swelling of the pulp. Current treatment of deep decay that approaches the pulp involves the application of drugs that induce low-level inflammation in the dental pulp to promote its repair, but this treatment is sometimes insufficient. However, the unsuccessful treatment often resulted in pulpitis. The C5a-C5aR is the initial stage of the immune cascade response. Blocking the binding of C5a-C5aR can slow the immune response in the narrow pulp cavity, so that dental pulp cells have enough time to proliferate, migrate, and differentiate. In this study, we compared lipoteichoic acid (LTA) and lipopolysaccharides (LPS) at different concentrations and time points and used the C5aR antagonist W54011 to block the C5a-C5aR axis. The blocking effect was detected by analyzing the expression of C5a, C5aR, interleukin (IL)-6, and Toll-like receptors 2 and 4 (TLR-2, 4). Next, we determined the optimal concentration and duration of LTA and LPS treatment in combination with W54011. Based on our results, we selected 1.0 μg·mL-1 LPS treatment for 48 h to generate an inflammatory model of human dental pulp cells. We then regrouped the cells and conducted expression analyses to monitor the expression of C5a, C5aR, IL-6, and TLR-4 at the protein and mRNA levels. LPS stimulation for 48 h and treatment with W54011 for 48 h effectively inhibited inflammation and did not affect C5a expression. This study provides a basis for follow-up studies of W54011 in dental pulp cells.

Identification of Hub Genes Associated with Abnormal Endothelial Function in Early Coronary Atherosclerosis

Abnormal coronary endothelial function is an important step in the development of atherosclerosis. Coronary atherosclerosis is one of the main causes of death worldwide. We constructed a co-expression network to identify hub genes associated with abnormal coronary endothelial function in early coronary atherosclerosis. In brief, we used the GSE132651 dataset from the gene expression omnibus database. The top 5000 genes with greatest variances were used for weighted gene co-expression network analysis, and the module most strongly correlated with abnormal coronary endothelial function was chosen as key module. Functional enrichment analysis was performed for genes in the key module, a protein-protein interaction network was constructed to find hub genes, and gene set enrichment analysis (GSEA) was also performed. Genes were classified into 7 modules, with the midnightblue module being the one that was most related to abnormal coronary endothelial function and containing genes enriched in DNA replication, cell cycle, nucleotide excision repair, and Human T-cell leukemia virus 1 infection. We identified nine hub genes (HOXC5, PRND, PADI3, RC3H1, DAPP1, SIT1, DRICH1, GPRIN2, and RHO), which differently expressed in abnormal and normal coronary endothelial function samples. GSEA suggested that samples associated with abnormal coronary endothelial function and highly expressed hub genes were linked with immune, coagulation, hypoxia, and angiogenesis processes. These hub genes, their expression pattern, and pathways may be involved in the development of abnormal coronary endothelial function and promotion of early coronary atherosclerosis.

Expression of Blood Cells Associated CD Markers and Cardiovascular Diseases: Clinical Applications in Prognosis

BACKGROUND

Cardiovascular diseases (CVDs) are a major cause of mortality worldwide. The results of various studies have shown that abnormality in the frequency and function of blood cells can be involved in CVD complications. In this review, we have focused on abnormalities in the expression of the CD (cluster of differentiation) markers of blood cells to assess the association of these abnormalities with CVD prognosis.

METHODS

We identified the relevant literature through a PubMed search (1990-2018) of English-language articles using the terms "Cardiovascular diseases", "CD markers", "leukocytes", "platelets", and "endothelial cells".

RESULTS

There is a variety of mechanisms for the effect of CD-marker expressions on CVDs prognosis, ranging from proinflammatory processes to dysfunctional effects in blood cells.

CONCLUSION

Considering the possible effects of CD-marker expression on CVDs prognosis, particularly prognosis of acute myocardial infarction and atherosclerosis, long-term studies in large cohorts are required to identify the prognostic value of CD markers and to target them with appropriate therapeutic agents.

Time-dependent C5a and C5aR expression in dental pulp cells following stimulation with LTA and LPS

Clinically, deep decay can lead to inflammation in the dental pulp. Apart from the use of various materials to sooth the inflamed pulp, there is currently no adequate treatment, and the gold standard, calcium hydroxide, that is used to cover the dentin/pulp, has limited effect. Sometimes the pulp will remain infected and cause pulpitis, and ultimately, the pulp will need to be removed. The first principle of oral treatment is to protect the pulp. Therefore, it is necessary to study the immune response and regeneration of pulp cells in conditions of deep decay. Of the terminal complement system proteins, complement 5a (C5a) has the most potent effect compared to complement 3a (C3a) and complement 4a (C4a). C5a is 20- to 2,500-fold stronger than C3a and C4a. The purpose of this study was to elucidate the association between C5a, secreted by complement activation, and the duration of inflammation. Another key goal was to detect the expression of C5a and its receptor, complement 5a receptor (C5aR). To this end, the cells were divided into 4 groups as per stimulation with lipoteichoic acid (LTA) or lipopolysaccharide (LPS) as follows: i) The 1 µg/ml LTA group; ii) the 1 µg/ml LPS group; iii) the 1 µg/ml LTA and 1 µg/ml LPS group; and iv) the PBS-only group, which served as a control. There were 5 time points for all 4 groups: 1, 2, 3, 5 and 7 days. Reverse transcription-quantitative polymerase chain reaction was used to detect the gene expression levels of C5a, C5aR and interleukin (IL)-6 at different time points. Western blot analyses was carried out to detect the expression of C5aR. Transmission electron microscopy was also conducted to assess the ultra-structural features of dental pulp cells. The gene expression trends of C5a and C5aR mRNA were identical. C5a and C5aR mRNA was highly expressed on the second day of LTA or LPS stimulation. However, in the LTA and LPS co-stimulation group, C5a and C5aR mRNA were highly expressed on both the first and second day, with higher levels on the second day. IL-6 expression decreased as time progressed in the LTA only and in the LTA + LPS co-stimulation groups. However, a peak in its expression was observed on the second day in the LPS group. On the whole, this study demonstrates that a 1 µg/ml concentration of LTA and LPS stimulates human dental pulp cells to activate the expression of C5a.

Investigation of vascular endothelial dysfunction in the patients with age-related macular degeneration

PURPOSE

This study aims to evaluate the association between age-related macular degeneration (AMD) and cardiovascular disease by using the noninvasive flow-mediated dilation (FMD) test to show endothelial dysfunction as an indicator of subclinical atherosclerosis.

METHOD

Participants in this study included 30 dry AMD patients, 30 wet AMD patients, and 30 healthy controls without any systemic disease, including AMD. FMD and the intima media thickness (IMT) of the carotid artery were compared between the groups.

RESULTS

Comparison of FMD between the groups showed a 10.96% brachial artery dilation in the healthy controls, 3.99% in the dry AMD group, and 5.03% in the wet AMD group. While a significant difference was not observed between the wet and dry AMD groups, comparison of the control group to the wet and dry AMD groups yielded a significant difference. When brachial artery dilation below 7% was accepted as an abnormal FMD, 26.7% of the healthy controls, 66.7% of the dry AMD patients and 76.7% of the wet AMD patients were found to be abnormal. Similarly, while no significant difference was observed between the wet and dry AMD groups, comparison of the control group with the wet and dry AMD patients yielded a significant difference. When an IMT below 0.7 mm was accepted as abnormal, 26.7% of the healthy controls, 33.3% of the dry AMD, and 43.3% of the wet AMD were found to have an abnormal IMT. However, differences between the groups did not reach statistical significance.

CONCLUSIONS

In this study, use of the FMD test showed endothelial dysfunction among AMD patients. No significant differences were found between the dry and wet AMD patient groups.

Polymorphism of the complement 5 gene is associated with large artery atherosclerosis stroke in Chinese patients

Methods

C5 rs17611 genetic variants were investigated in 494 IS patients and 330 control individuals .Ischemic stroke was classified into subtypes and patients were assessed 90 days post-stroke with the modified Rankin Scale to determine stroke outcome.

Results

The presence of C5 polymorphism was associated with the incidence of large artery atherosclerosis (LAA)-subtype IS (n =2 00; p = 0.031), which even persisted after adjustment for covariates (OR = 1.518; 95%CI = 1.093-2.018; p = 0.013). However, no association was found between genotypes and the severity and outcome of stroke (p = 0.978; p = 0.296).

Conclusions

The C5 polymorphism might contribute to the risk of LAA-subtype IS independently of other known risk predictors.

Complement factors C1q, C3 and C5b-9 in the posterior sclera of guinea pigs with negative lens-defocused myopia

AIM

To investigate the expression of complement factors in the posterior scleral fibroblasts of guinea pigs with negative lens-defocused myopia.

METHODS

Eighteen guinea pigs were assigned randomly to two groups: the negative lens-defocused group (NLD group, n=9) and the normal control without treatment group (NC group, n=9). The effect of myopic induction was compared in three subgroups: eyes treated with a -10.00 D negative lens in the NLD group (NL group), eyes treated with a plano (0 D) lens in the NLD group (PL group), and untreated right eyes in the NC group (NC group). The following analyses were conducted at four weeks: examination of the refractive error via retinoscopy, assessment of complement C5b-9 expression in the posterior scleral fibroblasts using immunohistochemistry, and measurements of complement C1q and C3 protein levels in the posterior sclera by Western blot.

RESULTS

After an induction period of four weeks, a significant myopic shift was detected in the eyes of the NL group, relative to that of the PL and NC groups (P<0.05). Data analysis showed a significant increase in the percentage of C5b-9 immunopositive fibroblasts in the posterior sclera of the NL group eyes, compared to the PL group (q=11.50, P<0.001). Significantly higher levels of C1q (q=4.94, P=0.01) and C3 (q=4.07, P=0.03) protein were detected in the posterior sclera of NL group eyes, compared to the PL group. There were no significant difference between the PL and NC groups for C5b-9 (q=2.44, P=0.10), C1q (q=1.55, P=0.53) and C3 (q=0.98, P=0.77) in the posterior sclera.

CONCLUSION

The data from present study provide evidence of the up-regulation of C5b-9, C1q and C3 in the posterior scleral fibroblasts in a NLD myopic animal model. The results suggest that the complement system may be involved in the development of myopia.

Candidate pathway-based genome-wide association studies identify novel associations of genomic variants in the complement system associated with coronary artery disease

BACKGROUND

Genomic variants identified by genome-wide association studies (GWAS) explain <20% of heritability of coronary artery disease (CAD), thus many risk variants remain missing for CAD. Identification of new variants may unravel new biological pathways and genetic mechanisms for CAD. To identify new variants associated with CAD, we developed a candidate pathway-based GWAS by integrating expression quantitative loci analysis and mining of GWAS data with variants in a candidate pathway.

METHODS AND RESULTS

Mining of GWAS data was performed to analyze variants in 32 complement system genes for positive association with CAD. Functional variants in genes showing positive association were then identified by searching existing expression quantitative loci databases and validated by real-time reverse transcription polymerase chain reaction. A follow-up case-control design was then used to determine whether the functional variants are associated with CAD in 2 independent GeneID Chinese populations. Candidate pathway-based GWAS identified positive association between variants in C3AR1 and C6 and CAD. Two functional variants, rs7842 in C3AR1 and rs4400166 in C6, were found to be associated with expression levels of C3AR1 and C6, respectively. Significant association was identified between rs7842 and CAD (P=3.99×10(-6); odds ratio, 1.47) and between rs4400166 and CAD (P=9.30×10(-3); odds ratio, 1.24) in the validation cohort. The significant findings were confirmed in the replication cohort (P=1.53×10(-5); odds ratio, 1.37 for rs7842; P=8.41×10(-3); odds ratio, 1.21 for rs4400166).

CONCLUSIONS

Integration of GWAS with biological pathways and expression quantitative loci is effective in identifying new risk variants for CAD. Functional variants increasing C3AR1 and C6 expression were shown to confer significant risk of CAD for the first time.

Macrovascular involvement in a child with atypical hemolytic uremic syndrome

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) is a disorder of the complement system which leads to thrombotic microangiopathy. It is caused by either acquired or hereditary defects in the activation or regulation of the alternative complement pathway and is therefore considered to be a disease of local complement dysregulation in microvasculature with predominantly renal involvement. However, extrarenal manifestations are observed in approximately one-fifth of aHUS patients, with the myocardium and central nervous system (CNS) being involved most often. Additionally, there have been a few reports of aHUS with cerebral artery stenoses or periphereal gangrene, suggesting the possibility of 'macrovascular' involvement in aHUS.

CASE-DIAGNOSIS/TREATMENT

We present a child with early onset aHUS and a C3 gain-of-function mutation who developed cerebral artery stenoses, leading ultimately to death due to a massive stroke 9 days after successful renal transplantation under prophylactic eculizumab treatment. Similar cases described in the literature are also briefly summarized.

CONCLUSIONS

The disease course in our patient with aHUS confirms that dysregulated complement activation can induce arterial steno-occlusive lesions in the absence of acute episodes of HUS. Further studies are required to document the frequency of such macrovascular complications and the role of eculizumab treatment in preventing their development and progression.

Distinct associations of complement C3a and its precursor C3 with atherosclerosis and cardiovascular disease. The CODAM study

Complement C3 is a novel risk factor for cardiovascular disease (CVD), but the underlying mechanism is currently unknown. We determined the associations of the anaphylatoxin C3a, the activation product of C3, and of C3 itself with estimates of atherosclerosis and CVD. We studied associations of C3a and C3 with carotid intima-media thickness (cIMT), ankle-arm blood pressure index (AAIx) and CVD in cross-sectional analyses among 545 participants of the Cohort on Diabetes and Atherosclerosis Maastricht (CODAM) study (62% men, 59.4 ± 6.9 years) and examined effect modification by smoking. We conducted linear and logistic regression analyses with adjustments for age, sex, glucose metabolism status, lipids, adiposity, renal function, blood pressure, pack-years smoked, physical activity, use of medication and investigated mediation by inflammation. C3a was independently associated with cIMT (β=0.032 mm, [95% confidence interval: 0.004; 0.060]) and AAIx (β=-0.022, [-0.043; -0.001]), but C3 was not. Effect modification by smoking was only observed for CVD (P(smoking*C3a)=0.008, P(smoking*C3)=0.018), therefore these associations were stratified for smoking behaviour. Both C3a (odds ratio [OR] =2.96, [1.15; 7.62]) and C3 (OR =1.98, [1.21; 3.22]) were independently associated with CVD in heavy smokers. The association of C3 with CVD was independent of C3a. Low-grade inflammation did partially explain the association of C3a with AAIx, but not the other observed associations. This suggests that C3a and C3 have distinct roles in pathways leading to CVD. C3a may promote atherosclerosis and additionally advance CVD in heavy smokers. Conversely, C3 may be associated with CVD in heavy smokers via pathways other than atherosclerosis.

Immunology of age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness in aged individuals. Recent advances have highlighted the essential role of immune processes in the development, progression and treatment of AMD. In this Review we discuss recent discoveries related to the immunological aspects of AMD pathogenesis. We outline the diverse immune cell types, inflammatory activators and pathways that are involved. Finally, we discuss the future of inflammation-directed therapeutics to treat AMD in the growing aged population.

Complement system activation and endothelial dysfunction in patients with age-related macular degeneration (AMD): possible relationship between AMD and atherosclerosis

Age-related macular degeneration (AMD) shares several pathological and epidemiological similarities with systemic atherosclerosis (AS). First, an association between AS and AMD is apparent from the analyses of the histological and biochemical structure of atherosclerotic plaques in the vascular walls and retinal drusen, the hallmark of AMD. Second, there is considerable evidence implicating endothelial dysfunction in the pathogenesis of both disorders, and cellular oxidative stress appears to be a common denominator underlying this process. Moreover, there are observations that the complement system (CS) triggering inflammatory response contributes to the onset and advancement of both diseases. The CS plays a role in the generation of drusen and neovascularization in AMD as well as in vascular endothelium activation, cell damage and ultimately atherosclerotic plaque formation in the course of systemic arteriosclerosis. It is widely recognized that both AMD and AS are not only related to local stimulation of the CS, but also result in its systemic activation. In addition, a specific Y402H polymorphism of the complement inhibitor factor H has been found to be associated with the incidence of both AMD and AS. Here, we propose a linking hypothesis between CS activation, endothelial dysfunction and the pathogenesis of two common and age-related pathological processes, AS and AMD. We also discuss the potential therapeutic value of pharmacological modulation of CS activation in these disorders.

Elevated C1rC1sC1inh levels independently predict atherosclerotic coronary heart disease

Clinical studies as well as animal models emphasized the importance of the complement system in the pathogenesis of coronary atherosclerosis and cardiovascular diseases. Our aim was to examine the extent and clinical implication of complement system activation in patients with stable atherosclerotic coronary heart disease (ACHD). Seventy-six patients with stable angina pectoris (SAP) scheduled for elective coronary angiography were enrolled into the study. Percutaneous coronary intervention (PCI) was performed in 24 patients, in 27 patients (NOPCI group) the coronary angiography showed significant stenosis and bypass surgery (CABG) or optimal medical therapy (OMT) were advised, whereas in 25 patients the coronary angiography was negative (NC group). 115 volunteers served as healthy controls (HC). In all individuals, the plasma level of several complement activation products - C1rC1sC1inh, C3bBbP and SC5b-9 - were determined on admission, strictly before the coronary angiography. In patients with angiographically proven ACHD (PCI and NOPCI groups), the baseline C1rC1sC1inh levels were significantly higher compared to NC group and HC (p<0.0001, for both comparisons). According to the multiple logistic regression analysis, high C1rC1sC1inh level proved to be an independent biomarker of coronary heart disease (p<0.026, OR: 65.3, CI: 1.628-2616.284).

CONCLUSION

Activation of the classical complement pathway can be observed in angiographically proven coronary atherosclerosis. Elevated C1rC1sC1inh levels might represent an useful biomarker for coronary artery disease.

Influence of hypertension, obesity and nicotine abuse on quantitative and qualitative changes in acute-phase proteins in patients with essential hypertension

Background

Hypertension is a powerful risk factor for cardiovascular disease and frequently occurs in conjunction with obesity. Accumulative evidence suggests a link between inflammation and hypertension. The aim of study was to evaluate whether blood pressure, obesity and smoking may influence acute-phase response.

Material/Methods

Ninety-two patients with essential hypertension and 75 healthy volunteers as a control group were studied. In all subjects assessment of hsCRP, α1-acid glycoprotein (AGP), α1-antichymotrypsin, transferrin, α1-antitrypsin, and C3 and C4 complement were performed. Evaluation of glycosylation profile and reactivity coefficient (RC) for AGP was done by means of affinity immunoelectrophoresis with concanavalin A as a ligand.

Results

When compared to the controls, hypertensive subjects presented significantly higher hsCRP concentrations and lower transferrin level. Hypertensive patients had elevated AGP-AC. The intensification of the inflammatory reaction was greater in the subgroup of hypertensive patients smoking cigarettes. In obese hypertensives, elevated serum C3 complement level was found.

Conclusions

We conclude that arterial hypertension may evoke the acute-phase response in humans. Markers of acute-phase response are particularly strongly expressed in smokers. Serum C 3 complement, but not other APPs, is elevated in hypertension coexisting with obesity.

The role of complement in the development and manifestation of murine atherogenic inflammation: novel avenues

Atherosclerosis is a chronic progressive inflammatory disease which manifests in the arterial vascular tree. It is a major cause of cardiovascular morbidity and contributes significantly to mortality in the developed world. Triggers for this inflammatory process are elevated levels of cholesterol, bacterial infection and obesity. The immune response in atherosclerosis is essentially pro-atherogenic, leading to lipid accumulation and cellular changes within the arterial wall. Small-animal models of atherosclerosis are used to study the relevance of candidate factors (cells, genes, diets) in the development and progression of lesions. From a multidisciplinary viewpoint, there are challenges and limitations to this approach. Activation of complement determines or modifies the outcome of acute and chronic inflammation. This review dissects the role of complement in the early development as well as the progressive manifestation of murine atherosclerosis and the advances in knowledge provided by the use of specific mouse models. It gives a critical overview of existing models, analyses seemingly conflicting results obtained with complement-deficient mouse models, highlights the importance of interrelationships between pro-coagulpant activity, adipose tissue, macrophages and complement, and uncovers exciting avenues of topical research.

Complement in atherosclerosis: friend or foe?

Atherosclerosis is a chronic inflammatory disease and the complement system plays a central role in innate immunity. Increasing evidence exists that the complement system is activated within atherosclerotic plaques. However, the role of complement in atherogenesis is not fully understood. Whereas complement activation by the classic and lectin pathway may be protective by removing apoptotic cells and cell debris from atherosclerotic plaques, activation of the complement cascade by the alternative pathway and beyond the C3 convertase with formation of anaphylatoxins and the terminal complement complex may be proatherogenic and may play a role in plaque destabilization leading to its rupture and the onset of acute cardiovascular events. In this review article we present evidence for complement activation within atherosclerotic plaques and we discuss recent data derived from experimental animal models that suggest a dual role of complement in the development of the disease. In addition, we summarize the role of complement components as biomarkers for cardiovascular disease.