Serum C5a Research Articles

Erythropoietin Effect on Complement Activation in Chronic Kidney Disease.

The complement system is an important part of innate immunity. Despite its known protective role, the complement system may contribute to increased inflammation and tissue injury in cases where its balanced activation is disrupted. The kidneys have been shown to be largely affected by complement dysregulation. The aim of the present study was to investigate the effect of erythropoietin administration, on the complement system, in chronic kidney disease patients. The study involved 20 patients with CKD who received erythropoietin and measurements of levels of complement factors C3a and C5a and complement regulatory proteins (CregPs) CD55, CD46, and CD59. An increase in serum C3a and C5a levels was observed in response to EPO therapy. The increase in C3a was statistically significant (p < 0.05) and concurrent with a statistically significant decrease in CD55 in CD4+ T cells (p < 0.05) and B cells (p < 0.05) and CD59 levels in CD4+ and CD8+ T cells (p < 0.05) at completion of EPO therapy compared with healthy controls. The above observations demonstrate that EPO induces complement activation in patients undergoing EPO therapy with a simultaneous restriction of CRegPs expression, thus possibly allowing the uncontrolled complement activation, which may contribute to tissue injury and disease progression.

Clinical values of serum C5a in Alzheimer’s disease patients with different dementia stages

Alzheimer’s disease (AD) is characterized by abnormal inflammatory responses, and complement C5a (C5a) is known to initiate inflammation. This study aimed to investigate the associations between serum C5a, inflammatory responses, and cognitive function in AD patients. A total of 242 AD patients and 132 age-matched controls were included. Enzyme-linked immunosorbent assay revealed increased levels of C5a, interleukin (IL)-4, IL-6, IL-10, IL-1β, and tumor necrosis factor (TNF)-α with advancing stages of AD. Pearson correlation coefficient and receiver operating characteristic curve revealed positive correlations between serum C5a levels, inflammatory cytokine levels, Neuropsychiatric Inventory (NPI) and Activities of Daily Living (ADL) scores, and negative correlations with Mini-mental State Examination (MMSE) and Montreal cognitive assessment (MoCA) scores. Serum C5a above 68.68 pg/mL could aid in the diagnosis of AD. Multivariable logistic analysis revealed that serum C5a was an independent risk factor for IL-1β/IL-6/IL-10/TNF-α and an independent protective factor for IL-4. Higher serum C5a levels were associated with lower MMSE and MoCA scores. In conclusion, elevated serum C5a levels were beneficial for AD diagnosis and predictive of inflammation and cognitive dysfunction.

Enhancing prognostic prediction of invasive candidiasis among cancer patients with a serum C5a-based scoring model.

Invasive candidiasis poses a life-threatening risk, and early prognosis assessment is vital for timely interventions to reduce mortality. Serum C5a levels have recently been linked to prognosis, but confirmation in cancer patients is pending. We detected the concentrations of serum C5a in hospitalized cancer patients with invasive candidiasis from 2020 to 2023, and retrospectively analyzed the clinical data. 372 cases were included in this study, with a 90-day mortality rate of 21.8%. Candida albicans (48.7%) remained the predominant pathogen, followed by Candida glabrata (25.5%), Candida tropicalis (12.4%), and Candida parapsilosis (8.3%). Gastrointestinal cancer was the most diagnosed pathology type (37.6%). Serum C5a demonstrated a noteworthy correlation with 90-day mortality, and employing a cutoff value of 36.7ng/ml revealed significantly higher 90-day mortality in low-C5a patients (41.2%) compared to high-C5a patients (6.3%) (p < 0.001). We also identified no source control, no surgery, metastasis, or chronic renal failure independently correlated with the 90-day mortality. Based on this, a prognostic model combining C5a and clinical parameters was constructed, which performed better than models built solely on C5a or clinical parameters. Furthermore, we weighted scores to each parameter in the model and presented diagnostic sensitivity and specificity corresponding to different score points calculated by the model. We constructed a prognostic scoring model including serum C5a and clinical parameters, which would contribute to precise prognosis assessment and benefit the outcome among cancer patients.

Indoor microbial exposure increases complement component C3a and C-reactive protein concentrations in serum

Indoor exposure to microbial growth, caused by moisture damage, has been an established health risk for several decades. It is likely that a damp indoor environment contains biological pollutants that trigger both the innate and adaptive branches of the immune system.In this study, we investigated the association between moisture damage related microbial exposure and serum C3a, C5a and CRP concentrations in Finnish adults.Serum C3a and CRP concentrations were elevated in individuals exposed to moisture damage and microbial growth in an indoor air environment. The elevated concentrations may be due to environmental factors present in moisture-damaged buildings. Complement activation and the resulting proinflammatory cleavage products may be a driving factor in inflammatory responses following exposure to indoor moisture damage and related microbial growth.

Correlation of serum complement factor 5a level with inflammatory response and cognitive function in patients with Alzheimer’s disease of different severity

BackgroundAlzheimer’s disease (AD) is a common cause of dementia. Serum complement factor 5a (C5a) is exceedingly implicated in AD. We explored the role of C5a levels in AD patients of different severity.MethodsMild, moderate, and severe AD patients, and healthy controls were included. C5a and pro-inflammatory factor (TNF-α, IL-1β, IL-6, CRP) levels were assessed by ELISA, and cognitive function was evaluated by Mini-Mental state examination (MMSE) score. The correlations between C5a, inflammatory factor levels, MMSE score, and plasma Aβ42/Aβ40 ratio were analyzed by Pearson tests. Independent risk factors for AD aggravation were assessed by logistic multivariate regression analysis. According to the cut-off value of receiver operating characteristic (ROC) curve analysis of C5a level, AD patients were assigned into low/high expression groups, and severe AD incidence was compared. Severe AD cumulative incidence was analyzed by Kaplan-Meier curve.ResultsSerum C5a, TNF-α, IL-1β, IL-6 and CRP levels were raised, and MMSE score was lowered in AD. Serum C5a, TNF-α, IL-1β, IL-6 and CRP levels in severe AD patients were higher than those in mild/moderate AD patients, but there were no significant differences in these cytokines between moderate and mild AD groups. The MMSE score of severe AD patients was lower than that of mild/moderate AD patients. Serum C5a level was positively correlated with serum TNF-α, IL-1β, IL-6, and CRP levels, and negatively correlated with MMSE score, with no obvious correlation with plasma Aβ42/Aβ40 ratio. Serum C5a level was one of the independent risk factors for AD aggravation. The occurrence of severe AD might be related to an increase in serum C5a level.ConclusionSerum C5a level increased with AD severity, and its expression was positively correlated with serum pro-inflammatory factor levels, and negatively correlated with cognitive function.

C5a-licensed phagocytes drive sterilizing immunity during systemic fungal infection

Systemic candidiasis is a common, high-mortality, nosocomial fungal infection. Unexpectedly, it has emerged as a complication of anti-complement C5-targeted monoclonal antibody treatment, indicating a critical niche for C5 in antifungal immunity. We identified transcription of complement system genes as the top biological pathway induced in candidemic patients and as predictive of candidemia. Mechanistically, C5a-C5aR1 promoted fungal clearance and host survival in a mouse model of systemic candidiasis by stimulating phagocyte effector function and ERK- and AKT-dependent survival in infected tissues. C5ar1 ablation rewired macrophage metabolism downstream of mTOR, promoting their apoptosis and enhancing mortality through kidney injury. Besides hepatocyte-derived C5, local C5 produced intrinsically by phagocytes provided a key substrate for antifungal protection. Lower serum C5a concentrations or a C5 polymorphism that decreases leukocyte C5 expression correlated independently with poor patient outcomes. Thus, local, phagocyte-derived C5 production licenses phagocyte antimicrobial function and confers innate protection during systemic fungal infection.

C5a Serum Levels in Patients with Endometriosis: A Cross-Sectional Study

ABSTRACT Endometriosis (EM) is a gynecological disorder that presents significant immune dysregulation in its pathophysiology. Recent studies indicate that the Complement System may play a significant role in the immune processes involved in peritoneal clearance and inflammation in EM patients. C5a is a potent anaphylatoxin molecule of complement associated with the development of inflammatory disorders, however its possible impact on EM development requires further investigation. The aim of this study was to determine the concentration of serum C5a in women with EM and to investigate its possible association with severity, symptoms, age and the timing of infertility. Ninety-four patients with EM (from stage I to IV) and 50 healthy controls were assessed for C5a serum levels. Clinical and demographic data were included in the analysis. C5a serum levels were higher in patients with EM than in controls (39.5 ng/mL vs. 26.0 ng/mL; p < .0001), but not different between the EM stages. No association was observed between C5a serum concentration and the presence of symptoms, age, symptom time or infertility time. The C5a serum levels were higher in patients with EM than in controls but not associated with the severity or clinical findings.

Predictive value of soluble CD59 for poor 28-day neurological prognosis and all-cause mortality in patients after cardiopulmonary resuscitation: a prospective observatory study

BackgroundsCD59, as a soluble form of CD59, is observed in multiple types of body fluids and correlated with the cell damage after ischemia/reperfusion injury. This study aims to observe the dynamic changes of serum sCD59 in patients after restoration of spontaneous circulation (ROSC) and explore the association of serum sCD59 with neurological prognosis and all-cause mortality in patients after ROSC.MethodsA total of 68 patients after ROSC were prospectively recruited and divided into survivors (n = 23) and non-survivors (n = 45) groups on the basis of 28-day survival. Twenty healthy volunteers were enrolled as controls. Serum sCD59 and other serum complement components, including sC5b-9, C5a, C3a, C3b, C1q, MBL, Bb, and pro-inflammatory mediators tumor necrosis factor (TNF)-α, interleukin-6 (IL-6), neurological damage biomarkers neuron-specific enolase (NSE) and soluble protein 100β (S100β) were measured by enzyme linked immunosorbent assay on day 1, 3, and 7 after ROSC. Neurologic outcome was assessed using cerebral performance category scores, with poor neurologic outcome defined as 3–5 points.ResultsIn the first week after ROSC, serum levels of sCD59, sC5b-9, C5a, C3a, C3b, C1q, MBL, Bb, TNF-α, IL-6, NSE and S100β were significantly elevated in patients after ROSC compared to healthy volunteers, with a significant elevation in the non-survivors compared to survivors except serum C1q and MBL. Serum sCD59 levels were positively correlated with serum sC5b-9, TNF-α, IL-6, NSE, S100β, SOFA score and APACHE II score. Moreover, serum sCD59 on day 1, 3, and 7 after ROSC could be used for predicting poor 28-day neurological prognosis and all-cause mortality. Serum sCD59 on day 3 had highest AUCs for predicting poor 28-day neurological prognosis [0.862 (95% CI 0.678–0.960)] and 28-day all-cause mortality [0.891 (95% CI 0.769–0.962)]. In multivariate logistic regression analysis, the serum level of sCD59D1 was independently associated with poor 28-day neurological prognosis and all-cause mortality.ConclusionsThe elevated serum level of sCD59 was positively correlated with disease severity after ROSC. Moreover, serum sCD59 could have good predictive values for the poor 28-day neurological prognosis and all-cause mortality in patients after ROSC.

404.6: The Suppression of Macrophage-Mediated Intestinal Transplant Rejection by C5a Receptor Antagonist

Background: Complement component C5a promotes alloreactivity via C5a receptor 1 (C5aR1) on immune cells. However, the role of C5a in small intestinal transplantation immunity has not been reported. During an inflammatory response, macrophages are activated by C5a and produce various inflammatory cytokines. In the present study, we examined the effect of the C5aR1 antagonist PMX53 on macrophage function following small intestinal transplantation. Methods: We established models by heterotopic intestinal transplantation using donor Dark Agouti and recipient Lewis rats. The rats were administered PMX53 starting on the day of operation until postoperative day 7. We assessed graft survival and performed HE staining of grafts and mixed lymphocyte reaction tests (MLR) using mixed cultures of T cells from lymph nodes and spleen cells from donors. Based on the complement activation results, we estimated serum levels of C5a and C5 mRNA levels in the graft on postoperative day 6. We also evaluated macrophage and T cell accumulation in the graft. To verify antibody-mediated rejection, we estimated anti-donor-specific antibodies in serum. Finally, we assessed the effect of PMX53 on macrophage differentiation and activation using bone marrow-derived macrophages (BMDMs). Results: Graft survival was significantly prolonged in the PMX53-treated group compared to that in the untreated group (6.6 vs 13.7 days, p<0.0001). PMX53 treatment inhibited shortening of the graft villus, as shown by the histological evaluation, and significantly lowered the stimulation index of the MLR when compared to the untreated group (2.2 vs 5.1, p<0.0001). In the untreated group, serum C5a and C5 mRNA levels in the graft were elevated. In the treated group, macrophages accumulation in the mesenteric lymph nodes of graft and monocytes in blood were reduced when compared with the untreated group (17.7% vs 7.9%, p=0.0007; 34.3% vs 20.7%, p=0.0005). Anti-donor-specific antibody levels in the treated and untreated groups were similar (MFI: 144.5 vs 116, p=0.068). PMX53 treatment decreased BMDM differentiation (CD11b/c+RT-1b+ cell: 56% vs 30%, p=0.001) as well as IL-1β and TNF-α mRNA expression levels in activated BMDMs (138 vs 45.8, p=0.0001 and 15.1 vs 4.22, p=0.0055). Conclusion: A C5a receptor antagonist suppresses rejection after small intestinal transplantation. Inhibition of C5a/C5aR1 signaling appears to regulate macrophage differentiation and activation.

The expression and clinical significance of neutrophil myeloperoxidase in patients with myeloperoxidase-antineutrophil cytoplasmic antibody associated vasculitis

Objective: To investigate the expression and clinical significance of neutrophil myeloperoxidase (MPO) in patients with MPO-antibody associated vasculitis (AAV). Methods: Thirty-six newly diagnosed MPO-AAV patients who were hospitalized in the First Affiliated Hospital, Anhui Medical University from July 2018 to June 2021 were enrolled,and 36 age and sex matched healthy subjects were selected as controls. Neutrophil MPO level was detected by flow cytometry (FCM) and MPO mRNA was tested by real time quantitative polymerase chain reaction (RT-qPCR) in all subjects. Serum complement fragment C5 (C5a) and MPO in both groups and serum MPO-anti-antineutrophilic cytoplasmic antibody(ANCA) in MPO-AAV group were measured by enzyme linked immunosorbent assay (ELISA), while the disease activity was evaluated by Birmingham vasculitis activity score-V3 (BVAS-V3). Results: Compared with the heathy control group, the expression of MPO mRNA in neutrophils, serum MPO and complement C5a in MPO-AAV group were significantly higher[MPO mRNA:30.2±11.5 vs. 1.9±0.6, P<0.001;MPO:(112.0±68.7) IU/L vs. (87.4±22.9) IU/L, P=0.01; C5a:(187.3±90.3) ng/ml vs. (107.3±31.1) ng/ml, P<0.001; respectively], while the mean fluorescence intensity (MFI) of MPO in neutrophils were significantly lower [ 1 343.3±723.4 vs. 2 868.0±1 136.5, P<0.001]. In MPO-AAV group, the expression of neutrophil MPO mRNA was positively correlated with serum MPO-ANCA and MPO levels (r=0.537, P=0.001 and r=0.358, P=0.032; respectively). Multiple regression analysis suggested that neutrophil MPO mRNA expression was positively correlated with serum MPO-ANCA level (β=0.695, P=0.006); neutrophil MPO level was negatively correlated with serum MPO-ANCA, MPO and complement C5a levels (r=-0.335, P=0.046; r=-0.372, P=0.026; r=-0.577, P<0.001; respectively). Further, neutrophil MPO level was negatively correlated with serum complement C5a level (β=-0.374, P=0.043). BVAS-V3 was positively correlated with MPO mRNA expression in neutrophils, serum MPO-ANCA, MPO and complement C5a (r=0.598, P<0.001; r=0.599, P<0.001; r=0.537, P=0.001; r=0.415, P=0.012; respectively) and negatively correlated with MPO level in neutrophils (r=-0.342, P=0.041). In multiple regression analysis it suggested that BVAS-V3 was positively correlated with MPO mRNA expression in neutrophils (β=0.511, P=0.002). Conclusion: In MPO-AAV patients, MPO synthesis and release in neutrophils are both significantly increased, which might be influenced by serum MPO-ANCA and C5a, respectively. Furthermore, MPO synthesis activity in neutrophils is an independent factor related to disease activity.

Mild Hypothermia Alleviates Complement C5a-Induced Neuronal Autophagy During Brain Ischemia-Reperfusion Injury After Cardiac Arrest.

After restoration of spontaneous circulation (ROSC) following cardiac arrest, complements can be activated and excessive autophagy can contribute to the brain ischemia-reperfusion (I/R) injury. Mild hypothermia (HT) protects against brain I/R injury after ROSC, but the mechanisms have not been fully elucidated. Here, we found that HT significantly inhibited the increases in serum NSE, S100β, and C5a, as well as neurologic deficit scores, TUNEL-positive cells, and autophagic vacuoles in the pig brain cortex after ROSC. The C5a receptor 1 (C5aR1) mRNA and the C5a, C5aR1, Beclin 1, LC3-II, and cleaved caspase-3 proteins were significantly increased, but the P62 protein and the PI3K/Akt/mTOR pathway-related proteins were significantly reduced in pigs after ROSC or neuronal oxygen-glucose deprivation/reoxygenation. HT could significantly attenuate the above changes in NT-treated neurons. Furthermore, C5a treatment induced autophagy and apoptosis and reduced the PI3K/Akt/mTOR pathway-related proteins in cultured neurons, which could be reversed by C5aR1 antagonist PMX205. Our findings demonstrated that C5a could bind to C5aR1 to induce neuronal autophagy during the brain I/R injury, which was associated with the inhibited PI3K/Akt/mTOR pathway. HT could inhibit C5a-induced neuronal autophagy by regulating the C5a-C5aR1 interaction and the PI3K/Akt/mTOR pathway, which might be one of the neuroprotective mechanisms underlying I/R injury. The C5a receptor 1 (C5aR1) mRNA and the C5a, C5aR1, Beclin 1, LC3-II, and cleaved caspase-3 proteins were significantly increased, but the P62 protein and the PI3K/Akt/mTOR pathway-related proteins were significantly reduced in pigs after ROSC or neuronal oxygen-glucose deprivation/reoxygenation. Mild hypothermia (HT) could significantly attenuate the above changes in NT-treated neurons. Furthermore, C5a treatment induced autophagy and apoptosis and reduced the PI3K/Akt/mTOR pathway-related proteins in cultured neurons, which could be reversed by C5aR1 antagonist PMX205. Proposed mechanism by which HT protects against brain I/R injury by repressing C5a-C5aR1-induced excessive autophagy. Complement activation in response to brain I/R injury generates C5a that can interact with C5aR1 to inactivate mTOR, probably through the PI3K-AKT pathway, which can finally lead to autophagy activation. The excessively activated autophagy ultimately contributes to cell apoptosis and brain injury. HT may alleviate complement activation and then reduce C5a-induced autophagy to protect against brain I/R injury. HT, mild hypothermia; I/R, ischemia reperfusion.

Circulating immune-complexes and complement activation through the classical pathway in myeloperoxidase-ANCA-associated glomerulonephritis

Background Anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (AAGN) is the fulminant glomerular diseases with poor renal prognosis. Activation of the complement system has recently been reported in the pathogenesis of AAGN, but it remains to be clarified as to which complement pathway is mainly involved. Methods 20 patients with myeloperoxidase (MPO)-AAGN were retrospectively evaluated. Using serum samples, circulating immune-complexes (CICs) were assessed by the monoclonal rheumatoid factor assay, and C5a and C5b-9 were assessed by ELISA. Complement activation through the classical pathway was further evaluated by the WIESLAB® Complement System Classical Pathway kit. The affinities of ANCAs were evaluated by a competitive inhibition method using ELISA, and were classified into the high, and low-affinity group. Deposition of complement components, such as C3, C5, C4d, C5b-9, factor Bb, mannan-binding lectin serine peptidase (MASP)-1, MASP-2, and mannose/mannan-binding lectin (MBL), in frozen renal sections were analyzed by immunofluorescence staining. Results CICs were found to be positive in 65% of the patients. All CIC-positive patients belonged to the high-affinity group. Furthermore, serum C5a and C5b-9 were significantly increased in MPO-AAGN patients, and these levels positively correlated with CIC levels. A significant negative correlation was also found between levels of WIESLAB® classical pathway kit and CICs. By immunofluorescence staining, glomerular deposition of C4d, C5, and C5b-9 were observed in similar distributions in MPO-AAGN patients, whereas the deposition of MASP-1, MASP-2, MBL, and factor Bb were minimal. Conclusions These results suggest the involvement of immune-complex induced complement activation through the classical pathway in the pathogenesis of MPO-AAGN.

Systemic Inflammation and Complement Activation Parameters Predict Clinical Outcome of Severe SARS-CoV-2 Infections.

Overactivation of the complement system has been characterized in severe COVID-19 cases. Complement components are known to trigger NETosis via the coagulation cascade and have also been reported in human tracheobronchial epithelial cells. In this longitudinal study, we investigated systemic and local complement activation and NETosis in COVID-19 patients that underwent mechanical ventilation. Results confirmed significantly higher baseline levels of serum C5a (24.5 ± 39.0 ng/mL) and TCC (11.03 ± 8.52 µg/mL) in patients compared to healthy controls (p < 0.01 and p < 0.0001, respectively). Furthermore, systemic NETosis was significantly augmented in patients (5.87 (±3.71) × 106 neutrophils/mL) compared to healthy controls (0.82 (±0.74) × 106 neutrophils/mL) (p < 0.0001). In tracheal fluid, baseline TCC levels but not C5a and NETosis, were significantly higher in patients. Kinetic studies of systemic complement activation revealed markedly higher levels of TCC and CRP in nonsurvivors compared to survivors. In contrast, kinetic studies showed decreased local NETosis in tracheal fluid but comparable local complement activation in nonsurvivors compared to survivors. Systemic TCC and NETosis were significantly correlated with inflammation and coagulation markers. We propose that a ratio comprising systemic inflammation, complement activation, and chest X-ray score could be rendered as a predictive parameter of patient outcome in severe SARS-CoV-2 infections.

Persistence of High Levels of Serum Complement C5a in Severe COVID-19 Cases After Hospital Discharge.

Evidence supports a role of complement anaphylatoxin C5a in the pathophysiology of COVID-19. However, information about the evolution and impact of C5a levels after hospital discharge is lacking. We analyzed the association between circulating C5a levels and the clinical evolution of hospitalized patients infected with SARS-CoV-2. Serum C5a levels were determined in 32 hospitalized and 17 non-hospitalized patients from Clinica Universidad de Navarra. One hundred and eighty eight serial samples were collected during the hospitalization stay and up to three months during the follow-up. Median C5a levels were 27.71 ng/ml (25th to 75th percentile: 19.35-34.96) for samples collected during hospitalization, versus 16.76 ng/ml (12.90-25.08) for samples collected during the follow-up (p<0.001). There was a negative correlation between serum C5a levels and the number of days from symptom onset (p<0.001). C5a levels also correlated with a previously validated clinical risk score (p<0.001), and was associated with the severity of the disease (p<0.001). An overall reduction of C5a levels was observed after hospital discharge. However, elevated C5a levels persisted in those patients with high COVID-19 severity (i.e. those with a longest stay in the hospital), even after months from hospital discharge (p=0.020). Moreover, high C5a levels appeared to be associated with the presence of long-term respiratory symptoms (p=0.004). In conclusion, serum C5a levels remain high in severe cases of COVID-19, and are associated with the presence of respiratory symptoms after hospital discharge. These results may suggest a role for C5a in the long-term effects of COVID-19 infection.

Complement Initiation Varies by Sex in Intestinal Ischemia Reperfusion Injury.

Intestinal ischemia reperfusion (IR)-induced tissue injury represents an acute inflammatory response with significant morbidity and mortality. The mechanism of IR-induced injury is not fully elucidated, but recent studies suggest a critical role for complement activation and for differences between sexes. To test the hypothesis that complement initiation differs by sex in intestinal IR, we performed intestinal IR on male and female WT C57B6L/, C1q-/-, MBL-/-, or properdin (P)-/- mice. Intestinal injury, C3b and C5a production and ex vivo secretions were analyzed. Initial studies demonstrated a difference in complement mRNA and protein in male and female WT mice. In response to IR, male C1q-, MBL- and P-deficient mice sustained less injury than male WT mice. In contrast, only female MBL-/- mice sustained significantly less injury than female wildtype mice. Importantly, wildtype, C1q-/- and P-/- female mice sustained significant less injury than the corresponding male mice. In addition, both C1q and MBL expression and deposition increased in WT male mice, while only elevated MBL expression and deposition occurred in WT female mice. These data suggested that males use both C1q and MBL pathways, while females tend to depend on lectin pathway during intestinal IR. Females produced significantly less serum C5a in MBL-/- and P-/- mice. Our findings suggested that complement activation plays a critical role in intestinal IR in a sex-dependent manner.

Arginine Methylation of Hepatic hnRNPH Suppresses Complement Activation and Systemic Inflammation in Alcohol-Fed Mice.

Protein arginine methyl transferase 1 (PRMT1) is the main enzyme for cellular arginine methylation. It regulates many aspects of liver biology including inflammation, lipid metabolism, and proliferation. Previously we identified that PRMT1 is necessary for protection from alcohol‐induced liver injury. However, many PRMT1 targets in the liver after alcohol exposure are not yet identified. We studied the changes in the PRMT1‐dependent arginine methylated proteome after alcohol feeding in mouse liver using mass spectrometry. We found that arginine methylation of the RNA‐binding protein (heterogeneous nuclear ribonucleoprotein [hnRNP]) H1 is mediated by PRMT1 and is altered in alcohol‐fed mice. PRMT1‐dependent methylation suppressed hnRNP H1 binding to several messenger RNAs of complement pathway including complement component C3. We found that PRMT1‐dependent hnRNP H methylation suppressed complement component expression in vitro, and phosphorylation is required for this function of PRMT1. In agreement with that finding, hepatocyte‐specific PRMT1 knockout mice had an increase in complement component expression in the liver. Excessive complement expression in alcohol‐fed PRMT1 knockout mice resulted in further complement activation and an increase in serum C3a and C5a levels, which correlated with inflammation in multiple organs including lung and adipose tissue. Using specific inhibitors to block C3aR and C5aR receptors, we were able to prevent lung and adipose tissue inflammation without affecting inflammation in the liver or liver injury. Conclusion: Taken together, these data suggest that PRMT1‐dependent suppression of complement production in the liver is necessary for prevention of systemic inflammation in alcohol‐fed mice. C3a and C5a play a role in this liver–lung and liver–adipose interaction in alcohol‐fed mice deficient in liver arginine methylation.

Crosstalk between coagulation and complement activation promotes cardiac dysfunction in arrhythmogenic right ventricular cardiomyopathy.

Aims: We previously found that complement components are upregulated in the myocardium of patients with arrhythmogenic right ventricular cardiomyopathy (ARVC), and inhibiting the complement receptor C5aR reduces disease severity in desmin knockout (Des-/-) mice, a model for ARVC. Here, we examined the mechanism underlying complement activation in ARVC, revealing a potential new therapeutic target.Methods: First, immunostaining, RT-PCR and western blot were used to detect the expression levels of complement and coagulation factors. Second, we knocked out the central complement component C3 in Des-/- mice (ARVC model) by crossing Des-/- mice with C3-/- mice to explore whether complement system activation occurs independently of the conventional pathway. Then, we evaluated whether a targeted intervention to coagulation system is effective to reduce myocardium injury. Finally, the plasma sC5b9 level was assessed to investigate the role in predicting adverse cardiac events in the ARVC cohort.Results: The complement system is activated in the myocardium in ARVC. Autoantibodies against myocardial proteins provided a possible mechanism underlying. Moreover, we found increased levels of myocardial C5 and the serum C5a in Des-/-C3-/- mice compared to wild-type mice, indicating that C5 is activated independently from the conventional pathway, presumably via the coagulation system. Crosstalk between the complement and coagulation systems exacerbated the myocardial injury in ARVC mice, and this injury was reduced by using the thrombin inhibitor lepirudin. In addition, we found significantly elevated plasma levels of sC5b9 and thrombin in patients, and this increase was correlated with all-cause mortality.Conclusions: These results suggest that crosstalk between the coagulation and complement systems plays a pathogenic role in cardiac dysfunction in ARVC. Thus, understanding this crosstalk may have important clinical implications with respect to diagnosing and treating ARVC.

Complement Factor C5a Is Increased in Blood of Patients with Abdominal Aortic Aneurysm and Has Prognostic Potential for Aneurysm Growth

In this observational case-control study, circulating levels of complement factors C3a and C5a and leukotriene B4 (LTB4) were analysed in abdominal aortic aneurysm (AAA) patients regarding their association with diagnosis and prognosis. Serum C5a was significantly raised in AAA patients compared to healthy controls—median 84.5 ng/ml (IQR = 37.5 ng/ml) vs. 67.7 ng/ml (IQR = 26.2 ng/ml), p = 0.007—but was not elevated in patients with athero-occlusive disease. Serum C5a levels correlated significantly with the increase in maximum AAA diameter over the following 6 months (r = 0.319, p = 0.021). The median growth in the lowest quartile of C5a (< 70 ng/ml) was 50% less compared to the highest C5a quartile (> 101 ng/ml): 1.0 mm/6 months (IQR = 0.8 mm) vs. 2.0 mm/6 months (IQR = 1.5 mm), p = 0.014. A log-linear mixed model predicted AAA expansion based on current diameter and C5a level. To our knowledge, this is the first study linking complement activation, in particular C5a serum level, with AAA progression.Graphical

Neutralizing Complement C5a Protects Mice with Pneumococcal Pulmonary Sepsis

Community-acquired pneumonia and associated sepsis cause high mortality despite antibiotic treatment. Uncontrolled inflammatory host responses contribute to the unfavorable outcome by driving lung and extrapulmonary organ failure. The complement fragment C5a holds significant proinflammatory functions and is associated with tissue damage in various inflammatory conditions. The authors hypothesized that C5a concentrations are increased in pneumonia and C5a neutralization promotes barrier stabilization in the lung and is protective in pneumococcal pulmonary sepsis. The authors investigated regulation of C5a in pneumonia in a prospective patient cohort and in experimental pneumonia. Two complementary models of murine pneumococcal pneumonia were applied. Female mice were treated with NOX-D19, a C5a-neutralizing L-RNA-aptamer. Lung, liver, and kidney injury and the inflammatory response were assessed by measuring pulmonary permeability (primary outcome), pulmonary and blood leukocytes, cytokine concentrations in lung and blood, and bacterial load in lung, spleen, and blood, and performing histologic analyses of tissue damage, apoptosis, and fibrin deposition (n = 5 to 13). In hospitalized patients with pneumonia (n = 395), higher serum C5a concentrations were observed compared to healthy subjects (n = 24; 6.3 nmol/l [3.9 to 10.0] vs. 4.5 nmol/l [3.8 to 6.6], median [25 to 75% interquartile range]; difference: 1.4 [95% CI, 0.1 to 2.9]; P = 0.029). Neutralization of C5a in mice resulted in lower pulmonary permeability in pneumococcal pneumonia (1.38 ± 0.89 vs. 3.29 ± 2.34, mean ± SD; difference: 1.90 [95% CI, 0.15 to 3.66]; P = 0.035; n = 10 or 11) or combined severe pneumonia and mechanical ventilation (2.56 ± 1.17 vs. 7.31 ± 5.22; difference: 4.76 [95% CI, 1.22 to 8.30]; P = 0.011; n = 9 or 10). Further, C5a neutralization led to lower blood granulocyte colony-stimulating factor concentrations and protected against sepsis-associated liver injury. Systemic C5a is elevated in pneumonia patients. Neutralizing C5a protected against lung and liver injury in pneumococcal pneumonia in mice. Early neutralization of C5a might be a promising adjunctive treatment strategy to improve outcome in community-acquired pneumonia.

Cerebrospinal Fluid Profiles in Parkinson's Disease: No Accumulation of Glucosylceramide, but Significant Downregulation of Active Complement C5 Fragment.

As mutations in glucocerebrosidase 1 (GBA1) are a major risk factor for Parkinson's disease (PD), decreased GBA1 activity might play an important role in the pathogenesis of the disease. However, there are currently no reports on glucosylceramide levels in the cerebrospinal fluid (CSF) in PD. We investigated whether glucosylceramide accumulation and abnormal immune status in the brain are associated with PD. We measured glucosylceramide by liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) as well as levels of the active fragment of complement C5, C5a, in the CSF of 33 PD, 15 amyotrophic lateral sclerosis (ALS) and 22 neurologically normal control (NNC) subjects. Serum C5a levels in all PD and ALS cases and in a limited number of NNC subjects (n = 8) were also measured. C5a levels in CSF were significantly downregulated in PD compared with NNC. Moreover, CSF C5a/serum C5a ratio showed pronounced perturbations in PD and ALS patients. LC-ESI-MS/MS revealed a statistically significant accumulation of a specific subspecies of glucosylceramide (d18 : 1/C23 : 0 acyl chain fatty acid) in ALS, but not in PD. Interestingly, CSF glucosylceramide (d18 : 1/C23 : 0) exhibited a significant correlation with CSF C5a levels in PD, but not ALS. No correlation was observed between C5a levels or glucosylceramide subspecies content and disease duration, levodopa equivalent daily dose or Hoehn & Yahr staging in PD. Our findings demonstrate complement dysregulation without glucosylceramide accumulation in PD CSF. Furthermore, we found an association between a specific glucosylceramide subspecies and immune status in PD.