Molecular basis for a link between complement and the vascular complications of diabetes

The complement system and diabetic retinopathy

Diabetic retinopathy (DR) is one of the common microvascular complications of diabetes mellitus and is the main cause of visual impairment in diabetic patients. The pathogenesis of DR is still unclear. The complement system, as an important component of the innate immune system in addition to defending against the invasion of foreign microorganisms, is involved in the occurrence and development of DR through 3 widely recognized complement activation pathways, the complement regulatory system, and many other pathways. Molecules such as C3a, C5a, and membrane attacking complex, as important molecules of the complement system, are involved in the pathologenesus of DR, either through direct damaging effects or by activating cells (microglia, macroglia, etc.) in the retinal microenvironment to contribute to the pathological damage of DR indirectly. We review the integral association of the complement system and DR to further understand the pathogenesis of DR and possibly provide a new strategy for itstreatment.

Oxidative Stress: A Culprit in the Progression of Diabetic Kidney Disease

Diabetic kidney disease (DKD) is the principal culprit behind chronic kidney disease (CKD), ultimately developing end-stage renal disease (ESRD) and necessitating costly dialysis or kidney transplantation. The limited therapeutic efficiency among individuals with DKD is a result of our finite understanding of its pathogenesis. DKD is the result of complex interactions between various factors. Oxidative stress is a fundamental factor that can establish a link between hyperglycemia and the vascular complications frequently encountered in diabetes, particularly DKD. It is crucial to recognize the essential and integral role of oxidative stress in the development of diabetic vascular complications, particularly DKD. Hyperglycemia is the primary culprit that can trigger an upsurge in the production of reactive oxygen species (ROS), ultimately sparking oxidative stress. The main endogenous sources of ROS include mitochondrial ROS production, NADPH oxidases (Nox), uncoupled endothelial nitric oxide synthase (eNOS), xanthine oxidase (XO), cytochrome P450 (CYP450), and lipoxygenase. Under persistent high glucose levels, immune cells, the complement system, advanced glycation end products (AGEs), protein kinase C (PKC), polyol pathway, and the hexosamine pathway are activated. Consequently, the oxidant-antioxidant balance within the body is disrupted, which triggers a series of reactions in various downstream pathways, including phosphoinositide 3-kinase/protein kinase B (PI3K/Akt), transforming growth factor beta/p38-mitogen-activated protein kinase (TGF-β/p38-MAPK), nuclear factor kappa B (NF-κB), adenosine monophosphate-activated protein kinase (AMPK), and the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling. The disease might persist even if strict glucose control is achieved, which can be attributed to epigenetic modifications. The treatment of DKD remains an unresolved issue. Therefore, reducing ROS is an intriguing therapeutic target. The clinical trials have shown that bardoxolone methyl, a nuclear factor erythroid 2-related factor 2 (Nrf2) activator, blood glucose-lowering drugs, such as sodium-glucose cotransporter 2 inhibitors, and glucagon-like peptide-1 receptor agonists can effectively slow down the progression of DKD by reducing oxidative stress. Other antioxidants, including vitamins, lipoic acid, Nox inhibitors, epigenetic regulators, and complement inhibitors, present a promising therapeutic option for the treatment of DKD. In this review, we conduct a thorough assessment of both preclinical studies and current findings from clinical studies that focus on targeted interventions aimed at manipulating these pathways. We aim to provide a comprehensive overview of the current state of research in this area and identify key areas for future exploration.

Evaluation of the effects of dietary advanced glycation end products on inflammation

Advanced glycation end products (AGEs) are a large number of heterogeneous compounds formed by the glycation of proteins, fats or nucleic acids. Endogenous AGEs have been associated with various health problems such as obesity, type 2 diabetes mellitus and cardiovascular disease. Inflammation is thought to be one of the main mechanisms in the development of these disorders. Although AGEs are produced endogenously in the body, exogenous sources such as smoking and diet also contribute to the body pool. Therefore, when the AGE pool in the body rises above physiological levels, different pathological conditions may occur through various mechanisms, especially inflammation. While the effects of endogenous AGEs on the development of inflammation have been studied relatively extensively, and current evidence indicates that dietary AGEs (dAGEs) contribute to the body's AGE pool, it is not yet known whether dAGEs have the same effect on the development of inflammation as endogenous AGEs. Therefore, this review aimed to evaluate the results of cross-sectional and intervention studies to understand whether dAGEs are associated with inflammation and, if there is an effect on inflammation, through which mechanisms this effect might occur.

The role of complement in kidney disease

The complement cascade comprises soluble and cell surface proteins and is an important arm of the innate immune system. Once activated, the complement system rapidly generates large quantities of protein fragments that are potent mediators of inflammatory, vasoactive and metabolic responses. Although complement is crucial to host defence and homeostasis, its inappropriate or uncontrolled activation can also drive tissue injury. For example, the complement system has been known for more than 50 years to be activated by glomerular immune complexes and to contribute to autoimmune kidney disease. Notably, the latest research shows that complement is also activated in kidney diseases that are not traditionally thought of as immune-mediated, including haemolytic-uraemic syndrome, diabetic kidney disease and focal segmental glomerulosclerosis. Several complement-targeted drugs have been approved for the treatment of kidney disease, and additional anti-complement agents are being investigated in clinical trials. These drugs are categorically different from other immunosuppressive agents and target pathological processes that are not effectively inhibited by other classes of immunosuppressants. The development of these new drugs might therefore have considerable benefits in the treatment of kidney disease.

1-Amino-1-deoxy-d-fructose ("fructosamine") and its derivatives: An update

1-Amino-1-deoxy-d-fructose (fructosamine, FN) derivatives are omnipresent in all living organisms, as a result of non-enzymatic condensation and Amadori rearrangement reactions between free glucose and biogenic amines such as amino acids, polypeptides, or aminophospholipids. Over decades, steady interest in fructosamine was largely sustained by its role as a key intermediate structure in the Maillard reaction that is responsible for the organoleptic and nutritional value of thermally processed foods, and for pathophysiological effects of hyperglycemia in diabetes. New trends in fructosamine research include the discovery and engineering of FN-processing enzymes, development of advanced tools for hyperglycemia monitoring, and evaluation of the therapeutic potential of both fructosamines and FN-recognizing proteins. This article covers developments in the field of fructosamine and its derivatives since 2010 and attempts to ascertain challenges in future research.

Glomerular proteomic profiling reveals early differences between preexisting and de novo type 2 diabetes in human renal allografts

BACKGROUND

Diabetes mellitus (DM), either preexisting or developing after transplantation, remains a crucial clinical problem in kidney transplantation. To obtain insights into the molecular mechanisms underlying PTDM development and early glomerular damage before the development of histologically visible diabetic kidney disease, we comparatively analysed the proteome of histologically normal glomeruli from patients with PTDM and normoglycaemic (NG) transplant recipients. Moreover, to assess specificities inherent in PTDM, we also comparatively evaluated glomerular proteomes from transplant recipients with preexisting type 2 DM (T2DM).

METHODS

Protocol biopsies were obtained from adult NG, PTDM and T2DM patients one year after kidney transplantation. Biopsies were formalin-fixed and embedded in paraffin, and glomerular cross-sections were microdissected. A total of 4 NG, 7 PTDM and 6 T2DM kidney biopsies were used for the analysis. The proteome was determined by liquid chromatography-tandem mass spectrometry. Relative differences in protein abundance and significantly dysregulated pathways were analysed.

RESULTS

Proteins involved in cell adhesion, immune response, leukocyte transendothelial filtration, and cell localization and organization were less abundant in glomeruli from PTDM patients than in those from NG patients, and proteins associated with supramolecular fibre organization and protein-containing complex binding were more abundant in PTDM patients. Overall, proteins related to adherens and tight junctions and those related to the immune system, including leukocyte transendothelial migration, were more abundant in NG patients than in transplanted patients with DM, irrespective of the timing of its development. However, proteins included in cell‒cell junctions and adhesion, insulin resistance, and vesicle-mediated transport were all less abundant in PTDM patients than in T2DM patients.

CONCLUSIONS

The glomerular proteome profile differentiates PTDM from NG and T2DM, suggesting specific pathogenetic mechanisms. Further studies are warranted to validate these results, potentially leading to an improved understanding of PTDM kidney transplant pathophysiology and to the identification of novel biomarkers.

(Patho)Physiology of Glycosylphosphatidylinositol-Anchored Proteins I: Localization at Plasma Membranes and Extracellular Compartments

Glycosylphosphatidylinositol (GPI)-anchored proteins (APs) are anchored at the outer leaflet of plasma membranes (PMs) of all eukaryotic organisms studied so far by covalent linkage to a highly conserved glycolipid rather than a transmembrane domain. Since their first description, experimental data have been accumulating for the capability of GPI-APs to be released from PMs into the surrounding milieu. It became evident that this release results in distinct arrangements of GPI-APs which are compatible with the aqueous milieu upon loss of their GPI anchor by (proteolytic or lipolytic) cleavage or in the course of shielding of the full-length GPI anchor by incorporation into extracellular vesicles, lipoprotein-like particles and (lyso)phospholipid- and cholesterol-harboring micelle-like complexes or by association with GPI-binding proteins or/and other full-length GPI-APs. In mammalian organisms, the (patho)physiological roles of the released GPI-APs in the extracellular environment, such as blood and tissue cells, depend on the molecular mechanisms of their release as well as the cell types and tissues involved, and are controlled by their removal from circulation. This is accomplished by endocytic uptake by liver cells and/or degradation by GPI-specific phospholipase D in order to bypass potential unwanted effects of the released GPI-APs or their transfer from the releasing donor to acceptor cells (which will be reviewed in a forthcoming manuscript).

Immunoregulatory Sertoli Cell Allografts Engineered to Express Human Insulin Survive Humoral-Mediated Rejection

An effective treatment and possible cure for type 1 diabetes is transplantation of pancreatic islets. Unfortunately, transplanted islets are rejected by the immune system with humoral-mediated responses being an important part of rejection. Sertoli cells (SC), an immune regulatory cell shown to survive as allografts long-term without immunosuppressants, have the potential to be used as a cell-based gene therapy vehicle to deliver endogenous insulin-a possible alternative to islets. Previously, we transduced a mouse SC line to produce human insulin. After transplantation into diabetic mice, these cells consistently produced low levels of insulin with graft survival of 75% at 50 days post-transplantation. The object of this study was to assess humoral immune regulation by these engineered SC. Both nontransduced and transduced SC survived exposure to human serum with complement in vitro. Analysis of allografts in vivo at 20 and 50 days post-transplantation revealed that despite IgG antibody detection, complement factor deposition was low and grafts survived through 50 days post-transplantation. Furthermore, the transduced SC secreted elevated levels of the complement inhibitor C1q binding protein. Overall, this suggests SC genetically engineered to express insulin maintain their ability to prevent complement-mediated killing. Since inhibiting complement-mediated rejection is important for graft survival, further studies of how SC modifies the immune response could be utilized to advance the use of genetically engineered SC or to prolong islet allograft survival to improve the treatment of diabetes.

The Role of Early Pregnancy Maternal pGCD59 Levels in Predicting Neonatal Hypoglycemia-Subanalysis of the DALI Study

CONTEXT

Neonatal hypoglycaemia (NH) is the most common metabolic problem in infants born of mothers with gestational diabetes. Plasma glycated CD59 (pGCD59) is an emerging biomarker that has shown potential in identifying women at risk of developing gestational diabetes. The aim of this study was to assess the association between early maternal levels of pGCD59 and NH.

OBJECTIVE

The aim of this study was to assess the association between early pregnancy maternal levels of plasma glycated CD59 (pGCD59) and neonatal hypoglycemia (NH).

METHODS

This is an observational study of pregnant women with a prepregnancy body mass index (BMI) greater than or equal to 29 screened for eligibility to participate in the Vitamin D and Lifestyle Intervention for Gestational Diabetes (DALI) trial. This analysis included 399 pregnancies. Levels of pGCD59 were measured in fasting maternal samples taken at the time of a 75-g, 2-hour oral glucose tolerance test performed in early pregnancy (< 20 weeks). NH, the study outcome, was defined as a heel-prick capillary glucose level of less than 2.6 mmol/L within 48 hours of delivery.

RESULTS

We identified 30 infants with NH. Maternal levels of pGCD59 in early pregnancy were positively associated with the prevalence of NH (one-way analysis of variance, P < .001). The odds of NH were higher in infants from mothers in tertile 3 of pGCD59 levels compared to those from mothers in tertile 1 (odds ratio [OR]: 2.41; 95% CI, 1.03-5.63). However, this was attenuated when adjusted for maternal BMI (OR: 2.28; 95% CI, 0.96-5.43). The cross-validated area under the curve (AUC) was 0.64 (95% CI, 0.54-0.74), and adjusted for maternal BMI, age, and ethnicity, the AUC was 0.70 (95% CI, 0.56-0.78).

CONCLUSION

Although pGCD59 levels in early pregnancy in women with BMI greater than or equal to 29 are associated with NH, our results indicate that this biomarker by itself is only a fair predictor of NH.

The Complement Pathway: New Insights into Immunometabolic Signaling in Diabetic Kidney Disease

Significance: The metabolic disorder, diabetes mellitus, results in microvascular complications, including diabetic kidney disease (DKD), which is partly believe to involve disrupted energy generation in the kidney, leading to injury that is characterized by inflammation and fibrosis. An increasing body of evidence indicates that the innate immune complement system is involved in the pathogenesis of DKD; however, the precise mechanisms remain unclear. Recent Advances: Complement, traditionally thought of as the prime line of defense against microbial intrusion, has recently been recognized to regulate immunometabolism. Studies have shown that the complement activation products, Complement C5a and C3a, which are potent pro-inflammatory mediators, can mediate an array of metabolic responses in the kidney in the diabetic setting, including altered fuel utilization, disrupted mitochondrial respiratory function, and reactive oxygen species generation. In diabetes, the lectin pathway is activated via autoreactivity toward altered self-surfaces known as danger-associated molecular patterns, or via sensing altered carbohydrate and acetylation signatures. In addition, endogenous complement inhibitors can be glycated, whereas diet-derived glycated proteins can themselves promote complement activation, worsening DKD, and lending support for environmental influences as an additional avenue for propagating complement-induced inflammation and kidney injury. Critical Issues: Recent evidence indicates that conventional renoprotective agents used in DKD do not target the complement, leaving this web of inflammatory stimuli intact. Future Directions: Future studies should focus on the development of novel pharmacological agents that target the complement pathway to alleviate inflammation, oxidative stress, and kidney fibrosis, thereby reducing the burden of microvascular diseases in diabetes. Antioxid. Redox Signal. 37, 781-801.

Crescents, an Independent Risk Factor for the Progression of Type 2 Diabetic Kidney Disease

CONTEXT

Crescents have been noticed in pathologic changes in patients with diabetic kidney disease (DKD). However, the clinical significance of crescents is still not well recognized.

OBJECTIVE

The main objective was to investigate the association between crescents and the prognoses of type 2 DKD (T2DKD) patients, and, secondly, to analyze the relationship between crescents and clinicopathologic features.

METHODS

A retrospective cohort study of 155 patients with T2DKD diagnosed by renal biopsy was carried out in a single center. Clinicopathologic features of patients with or without crescents were analyzed. Cox regression models and meta-analysis were used to determine the prognostic values of crescents for T2DKD. A nomogram was constructed to provide a simple estimation method of 1, 3, and 5-year renal survival for patients with T2DKD.

RESULTS

Compared with T2DKD patients without crescents, patients with crescents had higher 24-hour proteinuria and serum creatinine levels, as well as more severe Kimmelstiel-Wilson (K-W) nodules, segmental sclerosis (SS), and mesangiolysis (all P < .05). Furthermore, the crescents were positively correlated with serum creatinine, 24-hour proteinuria, K-W nodules, SS, mesangiolysis, and complement 3 deposition. Multivariate Cox models showed that crescents were an independent prognostic risk factor for renal survival (hazard ratio [HR] 2.68, 95% CI 1.27-5.64). The meta-analyzed results of 4 studies on crescents in T2DKD confirmed that patients with crescents had a significantly higher HR for renal progression.

CONCLUSION

Patients with crescents in T2DKD have more severe clinicopathologic changes and worse prognoses. The crescent can serve as an independent risk factor for T2DKD progression.

Complement membrane attack complex is an immunometabolic regulator of NLRP3 activation and IL-18 secretion in human macrophages

The complement system is an ancient and critical part of innate immunity. Recent studies have highlighted novel roles of complement beyond lysis of invading pathogens with implications in regulating the innate immune response, as well as contributing to metabolic reprogramming of T-cells, synoviocytes as well as cells in the CNS. These findings hint that complement can be an immunometabolic regulator, but whether this is also the case for the terminal step of the complement pathway, the membrane attack complex (MAC) is not clear. In this study we focused on determining whether MAC is an immunometabolic regulator of the innate immune response in human monocyte-derived macrophages. Here, we uncover previously uncharacterized metabolic changes and mitochondrial dysfunction occurring downstream of MAC deposition. These alterations in glycolytic flux and mitochondrial morphology and function mediate NLRP3 inflammasome activation, pro-inflammatory cytokine release and gasdermin D formation. Together, these data elucidate a novel signalling cascade, with metabolic alterations at its center, in MAC-stimulated human macrophages that drives an inflammatory consequence in an immunologically relevant cell type.

The Diagnostic Accuracy of Second Trimester Plasma Glycated CD59 (pGCD59) to Identify Women with Gestational Diabetes Mellitus Based on the 75 g OGTT Using the WHO Criteria: A Prospective Study of Non-Diabetic Pregnant Women in Ireland

The aim of this study was to evaluate the ability of second trimester plasma glycated CD59 (pGCD59), a novel biomarker, to predict the results of the 2 h 75 g oral glucose tolerance test at 24−28 weeks of gestation, employing the 2013 World Health Organisation criteria. This was a prospective study of 378 pregnant women. The ability of pGCD59 to predict gestational diabetes (GDM) was assessed using adjusted ROC curves for maternal age, BMI, maternal ethnicity, parity, previous GDM, and family history of diabetes. The pGCD59 levels were significantly higher in women with GDM compared to women with normal glucose tolerance (p = 0.003). The pGCD59 generated an adjusted AUC for identifying GDM cases of 0.65 (95%CI: 0.58−0.71, p < 0.001). The pGCD59 predicted GDM status diagnosed by a fasting glucose value of 5.1 mmol/L with an adjusted AUC of 0.74 (95%CI: 0.65−0.81, p < 0.001). Analysis of BMI subgroups determined that pGCD59 generated the highest AUC in the 35 kg/m2 ≤ BMI < 40 kg/m2 (AUC: 0.84 95%CI: 0.69−0.98) and BMI ≥ 40 kg/m2 (AUC: 0.96 95%CI: 0.86−0.99) categories. This study found that second trimester pGCD59 is a fair predictor of GDM status diagnosed by elevated fasting glucose independent of BMI and an excellent predictor of GDM in subjects with a very high BMI.

Plasma-glycated CD59 as an early biomarker for gestational diabetes mellitus: prospective cohort study protocol

INTRODUCTION

The significant maternal and neonatal outcomes of gestational diabetes mellitus (GDM) make it a major public health concern. Mothers with GDM are at greater risk of pregnancy complications and their offspring are at higher risk of diabetes and obesity. Currently, GDM is diagnosed with glucose load methods which are time-consuming and inconvenient to administer more than once during pregnancy; for this reason, there is a recognised need for a more accurate and simpler test for GDM. Previous studies indicate that plasma-glycated CD59 (pGCD59) is a novel biomarker for GDM. We present here the protocol of a prospective cohort study designed to (1) determine the accuracy of pGCD59 as an early, first trimester predictor of GDM and gestational impaired glucose tolerance and (2) assess the associations between pGCD59 levels and adverse maternal and neonatal outcomes.

METHODS AND ANALYSIS

We will obtain discarded plasma samples from pregnant women at two time points: first prenatal visit (usually <14 weeks gestation) and gestational weeks 24-28. A study-specific medical record abstraction tool will be used to obtain relevant maternal and neonatal clinical data from the EPIC clinical database. The prevalence of GDM will be determined using standard of care glucose load test results. We will determine the sensitivity and specificity of pGCD59 to predict the diagnosis of GDM and gestational impaired glucose tolerance, as well as the associations between levels of pGCD59 and the prevalence of maternal and neonatal outcomes.

ETHICS AND DISSEMINATION

This study has been approved by the Mass General Brigham Institutional Review Board (protocol 2011P002254). The results of this study will be presented at international meetings and disseminated in peer-reviewed journals.

Dysregulated Erythroid Mg2+ Efflux in Type 2 Diabetes

Hyperglycemia is associated with decreased Mg²⁺ content in red blood cells (RBC), but mechanisms remain unclear. We characterized the regulation of Mg²⁺ efflux by glucose in ex vivo human RBC. We observed that hemoglobin A_1C (HbA_1C) values correlated with Na⁺-dependent Mg²⁺ efflux (Na⁺/Mg²⁺ exchange) and inversely correlated with cellular Mg content. Treatment of cells with 50 mM D-glucose, but not with sorbitol, lowered total cellular Mg (2.2 ± 0.1 to 2.0 ± 0.1 mM, p < 0.01) and enhanced Na⁺/Mg²⁺ exchange activity [0.60 ± 0.09 to 1.12 ± 0.09 mmol/10¹³ cell × h (flux units, FU), p < 0.05]. In contrast, incubation with selective Src family kinase inhibitors PP2 or SU6656 reduced glucose-stimulated exchange activation (p < 0.01). Na⁺/Mg²⁺ exchange activity was also higher in RBC from individuals with type 2 diabetes (T2D, 1.19 ± 0.13 FU) than from non-diabetic individuals (0.58 ± 0.05 FU, p < 0.01). Increased Na⁺/Mg²⁺ exchange activity in RBC from T2D subjects was associated with lower intracellular Mg content. Similarly increased exchange activity was evident in RBC from the diabetic db/db mouse model as compared to its non-diabetic control (p < 0.03). Extracellular exposure of intact RBC from T2D subjects to recombinant peptidyl-N-glycosidase F (PNGase F) reduced Na⁺/Mg²⁺ exchange activity from 0.98 ± 0.14 to 0.59 ± 0.13 FU (p < 0.05) and increased baseline intracellular Mg content (1.8 ± 0.1 mM) to normal values (2.1 ± 0.1 mM, p < 0.05). These data suggest that the reduced RBC Mg content of T2D RBC reflects enhanced RBC Na⁺/Mg²⁺ exchange subject to regulation by Src family kinases and by the N-glycosylation state of one or more membrane proteins. The data extend our understanding of dysregulated RBC Mg²⁺ homeostasis in T2D.

C3c deposition predicts worse renal outcomes in patients with biopsy-proven diabetic kidney disease in type 2 diabetes mellitus

BACKGROUND

Although extensive efforts have been paid to identify reliable predictors for renal outcomes of diabetic kidney disease (DKD) patients in type 2 diabetes mellitus (T2DM), there are still only a limited number of predictive factors for DKD progression. Increasing evidence reported the role of the overactivated complement system in the pathogenesis of DKD. Whether renal complement depositions are associated with renal outcomes of DKD in T2DM is of interest.

METHODS

A total of 213 biopsy-proven DKD patients with T2DM were retrospectively recruited. Clinical and pathological data of the patients were analyzed. Kaplan-Meier analysis and Cox regression analysis were performed to explore predictors of end-stage renal disease (ESRD).

RESULTS

During a median follow-up of 23.0 (12.0, 39.0) months, 100/213 (46.9%) patients progressed to ESRD. C3c and C1q deposition were observed in 133/213 (62.4%) and 45/213 (21.1%) patients, respectively. Kaplan-Meier analysis revealed patients with C3c or C1q deposition had significantly worse renal outcomes compared with those without C3c or C1q deposition (p = .001 and p < .001, respectively). Univariate and multivariate Cox regression analysis demonstrated proteinuria (per 1 g/24 h increase, hazard ratio [HR] 1.134, 95% confidence interval [CI] [1.079, 1.191], p < .001), interstitial fibrosis and tubular atrophy score (score 2 and 3 vs. 0 and 1, HR 3.925, 95% CI [1.855, 8.304], p < .001), and C3c deposition (per 1+ increase, HR 1.299, 95% CI [1.073, 1.573], p = .007) were independent predictors for ESRD in DKD patients with T2DM.

CONCLUSIONS

C3c deposition in the kidney was associated with worse renal outcomes and was an independent predictor for ESRD in DKD patients with T2DM.

Association of Serum Complement C1q and C3 Level with Age-Related Macular Degeneration in Women

PURPOSE

To investigate the association between serum complement components and age-related macular degeneration (AMD).

PATIENTS AND METHODS

A total of 118 AMD patients and age- and sex-matched 106 control subjects were included. Demographic data and the level of serum complement component (C)1q, C3 and C4 were evaluated. Based on sex, the subjects were stratified into male and female subgroups.

RESULTS

The level of C1q (226.31±45.33mg/dL) was significantly higher and C3 (121.14±15.76mg/dL) was significantly lower than that in control group (200.03±38.54mg/dL) (128.42±19.81mg/dL) in the female AMD patients (p = 0.005, p = 0.045). Logistic regression showed that increased C1q (OR = 1.132, p = 0.016) and decreased C3 (OR = 0.960, p = 0.048) were independent risk factors for female AMD patients. No statistical significance was observed in the male.

CONCLUSION

Increased C1q and decreased C3 were associated with increased risk of AMD, suggesting that the complement classical pathway probably be involved in AMD, especially in female.

Effect of Comorbid Diabetes on Clinical Characteristics of COVID-19 Patients Infected by the Wild-Type or Delta Variant of SARS-CoV-2

BACKGROUND

Diabetes is one of the most common comorbidities in COVID-19 patients that pertains to disease severity, but the causal mechanism regarding its negative impact on COVID-19 outcome has yet been uncovered.

METHODS

We retrospectively analyzed 459 COVID-19 patients admitted in early 2020 and 336 COVID-19 patients admitted in August 2021, with their demographic information, medical history, vaccination status (if applied), and laboratory data reported.

RESULTS

Among COVID-19 patients, compared to the non-diabetic group, the diabetic group exhibited elder age, higher proportion of patients with other major comorbidities, more severe dysfunction of innate immune cells, more refractory blood coagulopathy and more detrimental organ damage. For the wild-type SARS-CoV-2 infection, diabetic comorbidity was associated with COVID-19 severity but not mortality, and the glycemic levels in the non-diabetic group upon infection experienced high and analogous to those in the diabetic group. Besides, infected by the delta variant of SARS-CoV-2, the non-diabetic patients did not demonstrate hyperglycemia, and despite different vaccination statuses, the diabetic patients exhibited comparable antibody responses to non-diabetic, showing the robustness of acquired immunity.

CONCLUSIONS

SARS-CoV-2 infection may superimpose the deterioration of innate immune systems in diabetic patients, which contributes to their worsened disease outcome, but timely COVID-19 immunization could provide adequate protection in diabetic population that leads to favored prognosis.

Renal diseases and the role of complement: Linking complement to immune effector pathways and therapeutics

The complement system is an ancient and phylogenetically conserved key danger sensing system that is critical for host defense against pathogens. Activation of the complement system is a vital component of innate immunity required for the detection and removal of pathogens. It is also a central orchestrator of adaptive immune responses and a constituent of normal tissue homeostasis. Once complement activation occurs, this system deposits indiscriminately on any cell surface in the vicinity and has the potential to cause unwanted and excessive tissue injury. Deposition of complement components is recognized as a hallmark of a variety of kidney diseases, where it is indeed associated with damage to the self. The provenance and the pathophysiological role(s) played by complement in each kidney disease is not fully understood. However, in recent years there has been a renaissance in the study of complement, with greater appreciation of its intracellular roles as a cell-intrinsic system and its interplay with immune effector pathways. This has been paired with a profusion of novel therapeutic agents antagonizing complement components, including approved inhibitors against complement components (C)1, C3, C5 and C5aR1. A number of clinical trials have investigated the use of these more targeted approaches for the management of kidney diseases. In this review we present and summarize the evidence for the roles of complement in kidney diseases and discuss the available clinical evidence for complement inhibition.

Activation of the Complement System in Patients with Cancer Cachexia

Simple Summary

Patients with cancer often suffer from severe weight loss as a result of the wasting of skeletal muscle and fat tissue. This has a strong negative impact on the patient’s prognosis and quality of life. Inflammation is thought to contribute to weight loss in cancer. To enable the future targeting of inflammation in patients with cancer who experience weight loss, we set out to characterize an important pro-inflammatory component of the immune system: the complement system. The blood levels of several elements of the complement system were analyzed in patients with and without weight loss and inflammation. We found that complement factors were activated specifically in patients with both weight loss and inflammation. Since complement inhibitory drugs are already on the market, these findings may open new opportunities for treating inflammation-mediated weight loss in patients with cancer.

Abstract

Systemic inflammation is thought to underlie many of the metabolic manifestations of cachexia in cancer patients. The complement system is an important component of innate immunity that has been shown to contribute to metabolic inflammation. We hypothesized that systemic inflammation in patients with cancer cachexia was associated with complement activation. Systemic C3a levels were higher in cachectic patients with inflammation (n = 23, C-reactive protein (CRP) ≥ 10 mg/L) as compared to patients without inflammation (n = 26, CRP < 10 mg/L) or without cachexia (n = 13) (medians 102.4 (IQR 89.4–158.0) vs. 81.4 (IQR 47.9–124.0) vs. 61.6 (IQR 46.8–86.8) ng/mL, respectively, p = 0.0186). Accordingly, terminal complement complex (TCC) concentrations gradually increased in these patient groups (medians 2298 (IQR 2022–3058) vs. 1939 (IQR 1725–2311) vs. 1805 (IQR 1552–2569) mAU/mL, respectively, p = 0.0511). C3a and TCC concentrations were strongly correlated (r_s = 0.468, p = 0.0005). Although concentrations of C1q and mannose-binding lectin did not differ between groups, C1q levels were correlated with both C3a and TCC concentrations (r_s = 0.394, p = 0.0042 and r_s = 0.300, p = 0.0188, respectively). In conclusion, systemic inflammation in patients with cancer cachexia is associated with the activation of key effector complement factors. The correlations between C1q and C3a/TCC suggest that the classical complement pathway could play a role in complement activation in patients with pancreatic cancer.

Tipping the balance: intricate roles of the complement system in disease and therapy

The ability of the complement system to rapidly and broadly react to microbial intruders, apoptotic cells and other threats by inducing forceful elimination responses is indispensable for its role as host defense and surveillance system. However, the danger sensing versatility of complement may come at a steep price for patients suffering from various immune, inflammatory, age-related, or biomaterial-induced conditions. Misguided recognition of cell debris or transplants, excessive activation by microbial or damaged host cells, autoimmune events, and dysregulation of the complement response may all induce effector functions that damage rather than protect host tissue. Although complement has long been associated with disease, the prevalence, impact and complexity of complement’s involvement in pathological processes is only now becoming fully recognized. While complement rarely constitutes the sole driver of disease, it acts as initiator, contributor, and/or exacerbator in numerous disorders. Identifying the factors that tip complement’s balance from protective to damaging effects in a particular disease continues to prove challenging. Fortunately, however, molecular insight into complement functions, improved disease models, and growing clinical experience has led to a greatly improved understanding of complement’s pathological side. The identification of novel complement-mediated indications and the clinical availability of the first therapeutic complement inhibitors has also sparked a renewed interest in developing complement-targeted drugs, which meanwhile led to new approvals and promising candidates in late-stage evaluation. More than a century after its description, complement now has truly reached the clinic and the recent developments hold great promise for diagnosis and therapy alike.

Plasma glycated CD59 predicts postpartum glucose intolerance after gestational diabetes

AIM

To assess whether in women with gestational diabetes mellitus (GDM), postpartum plasma glycated CD59 (pGCD59) levels predict conversion to glucose intolerance diagnosed with an oral glucose tolerance test (OGTT).

METHODS

Blood levels of pGCD59 were measured in a case-control study of 105 women with GDM who underwent a 75 g OGTT 3 months postpartum. The 35 postpartum glucose intolerant cases were individually matched for age, BMI, ethnic origin, and parity with 70 women with GDM but normal postpartum OGTT (controls). The GDM cohort (105) was also matched with 105 normal glucose tolerant women during pregnancy. pGCD59 was measured by ELISA in standard peptide units (SPU).

RESULTS

Mean pGCD59 postpartum was significantly higher in cases than in controls (1.5 ± 0.6 SPU vs 1.0 ± 0.6 SPU, P < 0.001). The area under the receiving operating characteristic curve (AUC) in cases vs controls was 0.72 (95% CI: 0.62-0.83) for postpartum pGCD59 and 0.50 (95% CI: 0.36-0.61) for postpartum HbA1c. A 0.5-unit increase in postpartum pGCD59 was associated with an odds ratio (OR) of 3.3 (95% CI: 1.82-6.16, P < 0.001) for glucose intolerance postpartum. A pGCD59 cut-off postpartum of 0.9 SPU had a sensitivity of 85.7% (95% CI: 69.7-95.2%), specificity of 47.8% (95% CI: 35.6-60.2%), positive predictive value of 45.4% (95% CI: 33.1-58.2%), and negative predictive value of 86.8% (95% CI: 71.9-95.6%). pGCD59 in pregnancy was a poor predictor for glucose intolerance postpartum (AUC of 0.61 (95% CI: 0.50-0.72)).

CONCLUSION

pGCD59 might identify women at low risk for glucose intolerance postpartum and could help to avoid an OGTT.

Complement in metabolic disease: metaflammation and a two-edged sword

We are currently experiencing an enduring global epidemic of obesity and diabetes. It is now understood that chronic low-grade tissue inflammation plays an important role in metabolic disease, brought upon by increased uptake of a so-called Western diet, and a more sedentary lifestyle. Many evolutionarily conserved links exist between metabolism and the immune system, and an imbalance in this system induced by chronic over-nutrition has been termed 'metaflammation'. The complement system is an important and evolutionarily ancient part of innate immunity, but recent work has revealed that complement not only is involved in the recognition of pathogens and induction of inflammation, but also plays important roles in cellular and tissue homeostasis. Complement can therefore contribute both positively and negatively to metabolic control, depending on the nature and anatomical site of its activity. This review will therefore focus on the interactions of complement with mechanisms and tissues relevant for metabolic control, obesity and diabetes.

Identification of Dysregulated Complement Activation Pathways Driven by N-Glycosylation Alterations in T2D Patients

Diabetes has become a major public health concern worldwide, most of which are type 2 diabetes (T2D). The diagnosis of T2D is commonly based on plasma glucose levels, and there are no reliable clinical biomarkers available for early detection. Recent advances in proteome technologies offer new opportunity for the understanding of T2D; however, the underlying proteomic characteristics of T2D have not been thoroughly investigated yet. Here, using proteomic and glycoproteomic profiling, we provided a comprehensive landscape of molecular alterations in the fasting plasma of the 24 Chinese participants, including eight T2D patients, eight prediabetic (PDB) subjects, and eight healthy control (HC) individuals. Our analyses identified a diverse set of potential biomarkers that might enhance the efficiency and accuracy based on current existing biological indicators of (pre)diabetes. Through integrative omics analysis, we showed the capability of glycoproteomics as a complement to proteomics or metabolomics, to provide additional insights into the pathogenesis of (pre)diabetes. We have newly identified systemic site-specific N-glycosylation alterations underlying T2D patients in the complement activation pathways, including decreased levels of N-glycopeptides from C1s, MASP1, and CFP proteins, and increased levels of N-glycopeptides from C2, C4, C4BPA, C4BPB, and CFH. These alterations were not observed at proteomic levels, suggesting new opportunities for the diagnosis and treatment of this disease. Our results demonstrate a great potential role of glycoproteomics in understanding (pre)diabetes and present a new direction for diabetes research which deserves more attention.

The pattern-recognition molecule H-ficolin in relation to diabetic kidney disease, mortality, and cardiovascular events in type 1 diabetes

H-ficolin recognizes patterns on microorganisms and stressed cells and can activate the lectin pathway of the complement system. We aimed to assess H-ficolin in relation to the progression of diabetic kidney disease (DKD), all-cause mortality, diabetes-related mortality, and cardiovascular events. Event rates per 10-unit H-ficolin-increase were compared in an observational follow-up of 2,410 individuals with type 1 diabetes from the FinnDiane Study. DKD progression occurred in 400 individuals. The unadjusted hazard ratio (HR) for progression was 1.29 (1.18–1.40) and 1.16 (1.05–1.29) after adjustment for diabetes duration, sex, HbA_1c, systolic blood pressure, and smoking status. After adding triglycerides to the model, the HR decreased to 1.07 (0.97–1.18). In all, 486 individuals died, including 268 deaths of cardiovascular causes and 192 deaths of complications to diabetes. HRs for all-cause mortality and cardiovascular mortality were 1.13 (1.04–1.22) and 1.05 (0.93–1.17), respectively, in unadjusted analyses. These estimates lost statistical significance in adjusted models. However, the unadjusted HR for diabetes-related mortality was 1.19 (1.05–1.35) and 1.18 (1.02–1.37) with the most stringent adjustment level. Our results, therefore, indicate that H-ficolin predicts diabetes-related mortality, but neither all-cause mortality nor fatal/non-fatal cardiovascular events. Furthermore, H-ficolin is associated with DKD progression, however, not independently of the fully adjusted model.

Identification of Novel Biomarker for Early Detection of Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common complications of diabetes mellitus. After development of DN, patients will progress to end-stage renal disease, which is associated with high morbidity and mortality. Here, we developed early-stage diagnostic biomarkers to detect DN as a strategy for DN intervention. For the DN model, Zucker diabetic fatty rats were used for DN phenotyping. The results revealed that DN rats showed significantly increased blood glucose, blood urea nitrogen (BUN), and serum creatinine levels, accompanied by severe kidney injury, fibrosis and microstructural changes. In addition, DN rats showed significantly increased urinary excretion of kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL). Transcriptome analysis revealed that new DN biomarkers, such as complementary component 4b (C4b), complementary factor D (CFD), C-X-C motif chemokine receptor 6 (CXCR6), and leukemia inhibitory factor (LIF) were identified. Furthermore, they were found in the urine of patients with DN. Since these biomarkers were detected in the urine and kidney of DN rats and urine of diabetic patients, the selected markers could be used as early diagnosis biomarkers for chronic diabetic nephropathy.

Emerging Protein Biomarkers for the Diagnosis or Prediction of Gestational Diabetes-A Scoping Review

Introduction: Gestational diabetes (GDM), defined as hyperglycemia with onset or initial recognition during pregnancy, has a rising prevalence paralleling the rise in type 2 diabetes (T2DM) and obesity. GDM is associated with short-term and long-term consequences for both mother and child. Therefore, it is crucial we efficiently identify all cases and initiate early treatment, reducing fetal exposure to hyperglycemia and reducing GDM-related adverse pregnancy outcomes. For this reason, GDM screening is recommended as part of routine pregnancy care. The current screening method, the oral glucose tolerance test (OGTT), is a lengthy, cumbersome and inconvenient test with poor reproducibility. Newer biomarkers that do not necessitate a fasting sample are needed for the prompt diagnosis of GDM. The aim of this scoping review is to highlight and describe emerging protein biomarkers that fulfill these requirements for the diagnosis of GDM. Materials and Methods: This scoping review was conducted according to preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines for scoping reviews using Cochrane Central Register of Controlled Trials (CENTRAL), the Cumulative Index to Nursing & Allied Health Literature (CINAHL), PubMed, Embase and Web of Science with a double screening and extraction process. The search included all articles published in the literature to July 2020. Results: Of the 3519 original database citations identified, 385 were eligible for full-text review. Of these, 332 (86.2%) were included in the scoping review providing a total of 589 biomarkers studied in relation to GDM diagnosis. Given the high number of biomarkers identified, three post hoc criteria were introduced to reduce the items set for discussion: we chose only protein biomarkers with at least five citations in the articles identified by our search and published in the years 2017-2020. When applied, these criteria identified a total of 15 biomarkers, which went forward for review and discussion. Conclusions: This review details protein biomarkers that have been studied to find a suitable test for GDM diagnosis with the potential to replace the OGTT used in current GDM screening protocols. Ongoing research efforts will continue to identify more accurate and practical biomarkers to take GDM screening and diagnosis into the 21st century.

Effect of dipeptidyl peptidase-4 inhibitors on complement activation

BACKGROUND

Adverse activation of the complement cascade in the innate immune system appears to be involved in development of vascular complications in diabetes. Dipeptidyl peptidase-4 (DPP-4) is a cell surface serine protease expressed in a variety of tissues. DPP-4 inhibitors are widely used in treatment of type 2 diabetes and appear to yield beneficial pleiotropic effects beyond their glucose-lowering action, for example, renoprotective and anti-inflammatory properties, but the exact mechanisms remain unknown. We hypothesised that DPP-4 inhibitors block adverse complement activation by inhibiting complement-activating serine proteases.

MATERIALS AND METHODS

We analysed the effects of 7 different DPP-4 inhibitors on the lectin and classical pathway of the complement system in vitro by quantifying complement factor C4b deposition onto mannan or IgG coated surfaces, respectively. Furthermore, plasma concentrations of mannan-binding lectin (MBL), soluble membrane attack complex (sMAC), and C4b deposition were quantified in 71 patients with a recent acute coronary syndrome and glucose disturbances, randomly assigned to sitagliptin 100 mg (n = 34) or placebo (n = 37) for 12 weeks.

RESULTS

All the 7 DPP-4 inhibitors tested in the study directly inhibited functional activity of the lectin pathway in a dose-dependent manner with varying potency in vitro. In vivo, MBL, sMAC, and C4b declined significantly during follow-up in both groups without significant effect of sitagliptin.

CONCLUSIONS

We demonstrated an inhibitory effect of DPP-4 inhibitors on the lectin pathway in vitro. The clinical relevance of this effect of DPP-4 inhibitors remains to be fully elucidated.

Novel Biochemical Markers of Glycemia to Predict Pregnancy Outcomes in Women With Type 1 Diabetes

OBJECTIVE

The optimal method of monitoring glycemia in pregnant women with type 1 diabetes remains controversial. This study aimed to assess the predictive performance of HbA_1c, continuous glucose monitoring (CGM) metrics, and alternative biochemical markers of glycemia to predict obstetric and neonatal outcomes.

RESEARCH DESIGN AND METHODS

One hundred fifty-seven women from the Continuous Glucose Monitoring in Women With Type 1 Diabetes in Pregnancy Trial (CONCEPTT) were included in this prespecified secondary analysis. HbA_1c, CGM data, and alternative biochemical markers (glycated CD59, 1,5-anhydroglucitol, fructosamine, glycated albumin) were compared at ∼12, 24, and 34 weeks' gestation using logistic regression and receiver operating characteristic (ROC) curves to predict pregnancy complications (preeclampsia, preterm delivery, large for gestational age, neonatal hypoglycemia, admission to neonatal intensive care unit).

RESULTS

HbA_1c, CGM metrics, and alternative laboratory markers were all significantly associated with obstetric and neonatal outcomes at 24 weeks' gestation. More outcomes were associated with CGM metrics during the first trimester and with laboratory markers (area under the ROC curve generally <0.7) during the third trimester. Time in range (TIR) (63-140 mg/dL [3.5-7.8 mmol/L]) and time above range (TAR) (>140 mg/dL [>7.8 mmol/L]) were the most consistently predictive CGM metrics. HbA_1c was also a consistent predictor of suboptimal pregnancy outcomes. Some alternative laboratory markers showed promise, but overall, they had lower predictive ability than HbA_1c.

CONCLUSIONS

HbA_1c is still an important biomarker for obstetric and neonatal outcomes in type 1 diabetes pregnancy. Alternative biochemical markers of glycemia and other CGM metrics did not substantially increase the prediction of pregnancy outcomes compared with widely available HbA_1c and increasingly available CGM metrics (TIR and TAR).

Complement, a Therapeutic Target in Diabetic Kidney Disease

Currently available treatments of diabetic kidney disease (DKD) remain limited despite improved understanding of DKD pathophysiology. The complement system is a central part of innate immunity, but its dysregulated activation is detrimental and results in systemic diseases with overt inflammation. Growing evidence suggests complement activation in DKD. With existent drugs and clinical success of treating other kidney diseases, complement inhibition has emerged as a potential novel therapy to halt the progression of DKD. This article will review DKD, the complement system's role in diabetic and non-diabetic disease, and the potential benefits of complement targeting therapies especially for DKD patients.

Exosomes: Biomarkers and Therapeutic Targets of Diabetic Vascular Complications

Diabetic vascular complications (DVC) including macrovascular and microvascular lesions, have a significant impact on public health, and lead to increased patient mortality. Disordered intercellular cascades play a vital role in diabetic systemic vasculopathy. Exosomes participate in the abnormal signal transduction of local vascular cells and mediate the transmission of metabolic disorder signal molecules in distant organs and cells through the blood circulation. They can store different signaling molecules in the membrane structure and release them into the blood, urine, and tears. In recent years, the carrier value and therapeutic effect of exosomes derived from stem cells have garnered attention. Exosomes are not only a promising biomarker but also a potential target and tool for the treatment of DVC. This review explored changes in the production process of exosomes in the diabetic microenvironment and exosomes' early warning role in DVC from different systems and their pathological processes. On the basis of these findings, we discussed the future direction of exosomes in the treatment of DVC, and the current limitations of exosomes in DVC research.

Sweet turning bitter: Carbohydrate sensing of complement in host defence and disease

The complement system plays a major role in threat recognition and in orchestrating responses to microbial intruders and accumulating debris. This immune surveillance is largely driven by lectins that sense carbohydrate signatures on foreign, diseased and healthy host cells and act as complement activators, regulators or receptors to shape appropriate immune responses. While carbohydrate sensing protects our bodies, misguided or impaired recognition can contribute to disease. Moreover, pathogenic microbes have evolved to evade complement by mimicking host signatures. While complement is recognized as a disease factor, we only slowly start to appreciate the role of carbohydrate interactions in the underlying processes. A better understanding of complement's sweet side will contribute to a better description of disease mechanisms and enhanced diagnostic and therapeutic options. This review introduces the key components in complement-mediated carbohydrate sensing, discusses their role in health and disease, and touches on the potential effects of carbohydrate-related disease intervention. LINKED ARTICLES: This article is part of a themed issue on Canonical and non-canonical functions of the complement system in health and disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.14/issuetoc.

A Covid-19 Patient with Complement-Mediated Coagulopathy and Severe Thrombosis

We report a patient with severe Covid-19-associated coagulopathy and type 2 diabetes mellitus who tested positive for antiphospholipid antibodies (aPL). Analysis of skin specimens suggested direct SARS-CoV-2 viral-induced and complement-mediated vascular injury and thrombosis, consistent with prior reports. Serial aPL testing demonstrated high levels of anticardiolipin antibodies (aCL) that declined to insignificant levels over a period of 5 weeks. SARS-CoV-2 RNA was detected in nasopharyngeal swab specimens on serial assays performed over the same 5-week period, though it was not detected thereafter. We hypothesize that SARS-CoV-2 viral-induced aPL contributed to severe Covid-19-associated coagulopathy in this patient.

Plasma CD59 concentrations are increased in preeclampsia with severe features and correlate with laboratory measures of end-organ injury

OBJECTIVES

Dysregulation of CD59 may lead to increased complement-mediated end-organ injury in preeclampsia. We sought to determine if soluble CD59 concentrations are altered in preeclampsia with severe features.

STUDY DESIGN

Observational case-control study, which enrolled subjects prospectively from six centers in Colombia from 2015 to 2016. Cases had preeclampsia with severe features and controls were either healthy or had chronic hypertension, gestational hypertension, or preeclampsia without severe features. Trained coordinators collected clinical data, blood and urine. Analyses were by test of medians and Spearman's correlation.

MAIN OUTCOME MEASURES

Soluble CD59 concentration in plasma and urine, using enzyme linked immunosorbent assays.

RESULTS

In total, 352 subjects were enrolled (104 cases; 248 controls). Compared to healthy women or those with other hypertensive disorders of pregnancy, women with preeclampsia with severe features had increased concentration of CD59 in plasma (P < 0.001) and decreased CD59 in urine (P = 0.01). In sub-group analyses, plasma CD59 concentrations were increased in preeclampsia with severe features compared to healthy controls (P < 0.001) or controls with either chronic hypertension (P = 0.002) or gestational hypertension (P = 0.02). Increased plasma CD59 concentrations correlated with decreased platelet count and increased lactate dehydrogenase, creatinine, aspartate transaminase, urine protein/creatinine ratio, systolic blood pressure and diastolic blood pressure (P < 0.01, all correlations).

CONCLUSION

In women with preeclampsia with severe features, soluble CD59 concentrations were increased in plasma and decreased in urine, and plasma levels correlated with increased blood pressure and end-organ injury. Soluble CD59 concentrations may help identify a subset of women with preeclampsia that have altered regulation of terminal complement proteins.

Complement in neurological disorders and emerging complement-targeted therapeutics

The complement system consists of a network of plasma and membrane proteins that modulate tissue homeostasis and contribute to immune surveillance by interacting with the innate and adaptive immune systems. Dysregulation, impairment or inadvertent activation of complement components contribute to the pathogenesis of some autoimmune neurological disorders and could even contribute to neurodegenerative diseases. In this Review, we summarize current knowledge about the main functions of the complement pathways and the involvement of complement in neurological disorders. We describe the complex network of complement proteins that target muscle, the neuromuscular junction, peripheral nerves, the spinal cord or the brain and discuss the autoimmune mechanisms of complement-mediated myopathies, myasthenia, peripheral neuropathies, neuromyelitis and other CNS disorders. We also consider the emerging role of complement in some neurodegenerative diseases, such as Alzheimer disease, amyotrophic lateral sclerosis and even schizophrenia. Finally, we provide an overview of the latest complement-targeted immunotherapies including monoclonal antibodies, fusion proteins and peptidomimetics that have been approved, that are undergoing phase I–III clinical trials or that show promise for the treatment of neurological conditions that respond poorly to existing immunotherapies.

In this Review, Dalakas et al. discuss the complement system, the role it plays in autoimmune neurological disease and neurodegenerative disease, and provide an overview of the latest therapeutics that target complement and that can be used for or have potential in neurological disorders.

Complement has an important physiological role in host immune defences and tissue remodelling.

The physiological role of complement extends to the regulation of synaptic development.

Complement has a key pathophysiological role in autoimmune neurological diseases and mediates the actions of pathogenic autoantibodies, such as acetylcholine receptor antibodies and aquaporin 4 antibodies.

For some autoimmune neurological diseases, such as myasthenia gravis and neuromyelitis optica spectrum disorders, approved complement-targeted treatments are now available.

Complement also seems to be of pathogenic relevance in neurodegenerative diseases such as Alzheimer disease, in which innate immune-driven inflammation is receiving increasing attention.

The field of complement-targeted therapeutics is rapidly expanding, with several FDA-approved agents and others currently in phase II and phase III clinical trials.

Identification of C3 as a therapeutic target for diabetic nephropathy by bioinformatics analysis

The pathogenesis of diabetic nephropathy is not completely understood, and the effects of existing treatments are not satisfactory. Various public platforms already contain extensive data for deeper bioinformatics analysis. From the GSE30529 dataset based on diabetic nephropathy tubular samples, we identified 345 genes through differential expression analysis and weighted gene coexpression correlation network analysis. GO annotations mainly included neutrophil activation, regulation of immune effector process, positive regulation of cytokine production and neutrophil-mediated immunity. KEGG pathways mostly included phagosome, complement and coagulation cascades, cell adhesion molecules and the AGE-RAGE signalling pathway in diabetic complications. Additional datasets were analysed to understand the mechanisms of differential gene expression from an epigenetic perspective. Differentially expressed miRNAs were obtained to construct a miRNA-mRNA network from the miRNA profiles in the GSE57674 dataset. The miR-1237-3p/SH2B3, miR-1238-5p/ZNF652 and miR-766-3p/TGFBI axes may be involved in diabetic nephropathy. The methylation levels of the 345 genes were also tested based on the gene methylation profiles of the GSE121820 dataset. The top 20 hub genes in the PPI network were discerned using the CytoHubba tool. Correlation analysis with GFR showed that SYK, CXCL1, LYN, VWF, ANXA1, C3, HLA-E, RHOA, SERPING1, EGF and KNG1 may be involved in diabetic nephropathy. Eight small molecule compounds were identified as potential therapeutic drugs using Connectivity Map.

Plasma glycated CD59 (gCD59), a novel biomarker for the diagnosis, management and follow up of women with Gestational Diabetes (GDM) - protocol for prospective cohort study

BACKGROUND

The prevalence of Gestational Diabetes (GDM) is rising and with it the number of mothers and children at risk of adverse outcomes. As treatment has been shown to reduce adverse events, it is imperative that we identify all at-risk pregnant women. In Ireland, the national standard of care is selective screening with a 2-hour 75 g oral glucose tolerance test (OGTT). Aiming for universal screening is of utmost importance but this is difficult given the length, the unfeasibility and impracticability of the OGTT. We aim to assess if the novel biomarker glycated CD59 (gCD59) is a suitable contender for the OGTT in identifying women with GDM.

METHODS

In this prospective cohort study, the study participants will be consecutive pregnant women at Galway University Hospital, Galway, Ireland. Samples for the plasma gCD59 biomarker will be taken together with routine bloods at the first antenatal visit, at weeks 24-28 at the time of routine 75 g OGTT, in trimester 3- and 12-weeks post-partum for women with GDM while having their routine post-partum 75 g OGTT. The constructed database will contain baseline information on each study participant, baseline laboratory data, follow-up laboratory data and pregnancy related outcomes. We aim to recruit a total of 2,000 participants over the project period and with a national GDM prevalence of 12-13%, we will have 240-260 subjects who meet OGTT criteria for GDM. Following regional prevalence, we expect to have 34-37 women who will develop either diabetes or pre-diabetes in the early post-partum period. The sensitivity and specificity of plasma gCD59 to predict the results of the OGTT will be assessed using nonparametric estimates of the receiver operating characteristic (ROC) curves and respective area under the ROC curve (AUROC).

DISCUSSION

A body of clinical and experimental evidence supports a link between the complement system, complement regulatory proteins, and the pathogenesis of diabetes complications. Building on this research, our study plans to look at the plasma gCD59 capacity to classify pregnant women with normal or abnormal glucose tolerance but also to assess if plasma gCD59 can be used as an early predictor for GDM, for adverse pregnancy outcomes and/or post-partum glucose intolerance.

Associations of dicarbonyl stress with complement activation: the CODAM study

AIMS/HYPOTHESIS

Reactive α-dicarbonyl compounds are major precursors of AGEs and may lead to glycation of circulating and/or cell-associated complement regulators. Glycation of complement regulatory proteins can influence their capacity to inhibit complement activation. We investigated, in a human cohort, whether greater dicarbonyl stress was associated with more complement activation.

METHODS

Circulating concentrations of dicarbonyl stress markers, i.e. α-dicarbonyls (methylglyoxal [MGO], glyoxal [GO] and 3-deoxyglucosone [3-DG]), and free AGEs (N^ε-(carboxymethyl)lysine [CML], N^ε-(carboxyethyl)lysine [CEL] and N^δ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine [MG-H1]), and protein-bound AGEs (CML, CEL, pentosidine), as well as the complement activation products C3a and soluble C5b-9 (sC5b-9), were measured in 530 participants (59.5 ± 7.0 years [mean ± SD], 61% men) of the Cohort on Diabetes and Atherosclerosis Maastricht (CODAM) study. Multiple linear regression analyses were used to investigate the associations between dicarbonyl stress (standardised) and complement activation (standardised) with adjustment of potential confounders, including age, sex, lifestyle, use of medication and markers of obesity. In addition, the associations of two potentially functional polymorphisms (rs1049346, rs2736654) in the gene encoding glyoxalase 1 (GLO1), the rate-limiting detoxifying enzyme for MGO, with C3a and sC5b-9 (all standardized) were evaluated.

RESULTS

After adjustment for potential confounders, plasma concentration of the dicarbonyl GO was inversely associated with sC5b-9 (β -0.12 [95% CI -0.21, -0.02]) and the protein-bound AGE CEL was inversely associated with C3a (-0.17 [-0.25, -0.08]). In contrast, the protein-bound AGE pentosidine was positively associated with sC5b-9 (0.15 [0.05, 0.24]). No associations were observed for other α-dicarbonyls and other free or protein-bound AGEs with C3a or sC5b-9. Individuals with the AG and AA genotype of rs1049346 had, on average, 0.32 and 0.40 SD lower plasma concentrations of sC5b-9 than those with the GG genotype, while concentrations of C3a did not differ significantly between rs1049346 genotypes. GLO1 rs2736654 was not associated with either C3a or sC5b-9.

CONCLUSIONS/INTERPRETATION

Plasma concentrations of dicarbonyl stress markers showed distinct associations with complement activation products: some of them were inversely associated with either C3a or sC5b-9, while protein-bound pentosidine was consistently and positively associated with sC5b-9. This suggests different biological relationships of individual dicarbonyl stress markers with complement activation.

Plasma Glycated CD59 Predicts Early Gestational Diabetes and Large for Gestational Age Newborns

CONTEXT

Gestational diabetes mellitus (GDM) diagnosed in early pregnancy is a health care challenge because it increases the risk of adverse outcomes. Plasma-glycated CD59 (pGCD59) is an emerging biomarker for diabetes and GDM. The aim of this study was to assess the performance of pGCD59 as a biomarker of early GDM and its association with delivering a large for gestational age (LGA) infant.

OBJECTIVES

To assess the performance of pGCD59 to identify women with GDM in early pregnancy (GDM < 20) and assess the association of pGCD59 with LGA and potentially others adverse neonatal outcomes linked to GDM.

METHODS

Blood levels of pGCD59 were measured in samples from 693 obese women (body mass index > 29) undergoing a 75-g, 2-hour oral glucose tolerance test (OGTT) at <20 weeks' gestation in the Vitamin D and Lifestyle Intervention study: the main analyses included 486 subjects who had normal glucose tolerance throughout the pregnancy, 207 who met criteria for GDM at <20 weeks, and 77 diagnosed with GDM at pregnancy weeks 24 through 28. Reference tests were 75-g, 2-hour OGTT adjudicated based on International Association of Diabetes and Pregnancy Study Group criteria. The index test was a pGCD59 ELISA.

RESULTS

Mean pGCD59 levels were significantly higher (P < 0.001) in women with GDM < 20 (3.9 ± 1.1 standard peptide units [SPU]) than in those without (2.7 ± 0.7 SPU). pGCD59 accurately identified GDM in early pregnancy with an area under the curve receiver operating characteristic curves of 0.86 (95% confidence interval [CI], 0.83-0.90). One-unit increase in maternal pGCD59 level was associated with 36% increased odds of delivering an LGA infant (odds ratio for LGA vs non-LGA infant: 1.4; 95% CI, 1.1-1.8; P = 0.016).

CONCLUSION

Our results indicate that pGCD59 is a simple and accurate biomarker for detection of GDM in early pregnancy and risk assessment of LGA.

Extracellular Vesicle-Induced Classical Complement Activation Leads to Retinal Endothelial Cell Damage via MAC Deposition

Several studies have suggested that there is a link between membrane attack complex (MAC) deposition in the retina and the progression of diabetic retinopathy (DR). Our recent investigation demonstrated that circulating IgG-laden extracellular vesicles contribute to an increase in retinal vascular permeability in DR through activation of the complement system. However, the mechanism through which extracellular vesicle-induced complement activation contributes to retinal vascular cytolytic damage in DR is not well understood. In this study, we demonstrate that IgG-laden extracellular vesicles in rat plasma activate the classical complement pathway, and in vitro Streptozotocin (STZ)-induced rat diabetic plasma results in MAC deposition and cytolytic damage in human retinal endothelial cells (HRECs). Moreover, removal of the plasma extracellular vesicles reduced the MAC deposition and abrogated cytolytic damage seen in HRECs. Together, the results of this study demonstrate that complement activation by IgG-laden extracellular vesicles in plasma could lead to MAC deposition and contribute to endothelium damage and progression of DR.

Complement activation in obesity, insulin resistance, and type 2 diabetes mellitus

Amplified inflammatory reaction has been observed to be involved in cardiometabolic diseases such as obesity, insulin resistance, diabetes, dyslipidemia, and atherosclerosis. The complement system was originally viewed as a supportive first line of defense against microbial invaders, and research over the past decade has come to appreciate that the functions of the complement system extend beyond the defense and elimination of microbes, involving in such diverse processes as clearance of the immune complexes, complementing T and B cell immune functions, tissue regeneration, and metabolism. The focus of this review is to summarize the role of the activation of complement system and the initiation and progression of metabolic disorders including obesity, insulin resistance and diabetes mellitus. In addition, we briefly describe the interaction of the activation of the complement system with diabetic complications such as diabetic retinopathy, nephropathy and neuropathy, highlighting that targeting complement system therapeutics could be one of possible routes to slow down those aforementioned diabetic complications.

Deficiency of C3a receptor attenuates the development of diabetic nephropathy

Objective

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease and end-stage renal disease. Emerging evidence suggests that complement activation is involved in the pathogenesis of DN. The aim of this study was to investigate the pathogenic role of C3a and C3a receptor (C3aR) in DN.

Research design and methods

The expression of C3aR was examined in the renal specimen of patients with DN. Using a C3aR gene knockout mice (C3aR-/-), we evaluated kidney injury in diabetic mice. The mouse gene expression microarray was performed to further explore the pathogenic role of C3aR. Then the underlying mechanism was investigated in vitro with macrophage treated with C3a.

Results

Compared with normal controls, the renal expression of C3aR was significantly increased in patients with DN. C3aR-/- diabetic mice developed less severe diabetic renal damage compared with wild-type (WT) diabetic mice, exhibiting significantly lower level of albuminuria and milder renal pathological injury. Microarray profiling uncovered significantly suppressed inflammatory responses and T-cell adaptive immunity in C3aR-/- diabetic mice compared with WT diabetic mice, and this result was further verified by immunohistochemical staining of renal CD4+, CD8+ T cells and macrophage infiltration. In vitro study demonstrated C3a can enhance macrophage-secreted cytokines which could induce inflammatory responses and differentiation of T-cell lineage.

Conclusions

C3aR deficiency could attenuate diabetic renal damage through suppressing inflammatory responses and T-cell adaptive immunity, possibly by influencing macrophage-secreted cytokines. Thus, C3aR may be a promising therapeutic target for DN.

Red blood cell distribution width and coronary artery disease severity in diabetic patients

Aim: The purpose of the study is to evaluate the relationship between red blood cell distribution width (RDW) and coronary calcium score in diabetic patients. Methods: Hematological parameters of 100 diabetic (Type II) patients were assessed. Computed tomographic angiography was used to asses coronary artery calcium (CAC) score. Results: Mean age of the study cohort was 55 years (males: 60%). Mean RDW was 12.7%. Mean CAC score was 243. There was a significant correlation between RDW and each of: CAC scores (r = 0.53; p < 0.001) and severity of coronary artery disease (CAD; r = 0.25; p = 0.047). A cut-off value >14.2% (receiver operating characteristic curves) predicted CAC score >400. A cut-off value >-14.6% predicted the presence of significant CAD. Conclusion: Diabetic patients with high-CAC scores and significant CAD had higher RDW.

Role of complement in diabetes

Accumulating evidence suggests a role for the complement system in the pathogenesis of diabetes and the vascular complications that characterise this condition. Complement proteins contribute to the development of type 1 diabetes (T1D) by enhancing the underlying organ-specific autoimmune processes. Complement upregulation and activation is also an important feature of insulin resistance and the development of type 2 diabetes (T2D). Moreover, animal and human studies indicate that complement proteins are involved in the pathogenic mechanisms leading to diabetic microvascular and macrovascular complications. The adverse vascular effects of complement appear to be related to enhancement of the inflammatory process and the predisposition to a thrombotic environment, eventually leading to vascular occlusion. Complement proteins have been considered as therapeutic targets to prevent or treat vascular disease but studies have been mainly conducted in animal models, while human work has been both limited and inconclusive so far. Further studies are needed to understand the potential role of complement proteins as therapeutic targets for reversal of the pathological processes leading to T1D and T2D and for the prevention/treatment of diabetic vascular complications.

Reduced IgE/IgG binding capacities of bovine α-Lactalbumin by glycation after dynamic high-pressure microfluidization pretreatment evaluated by high resolution mass spectrometry

Dynamic high-pressure microfluidization (DHPM) pretreatment and glycation with lactose were employed to modify α-Lactalbumin (α-LA) with respect to the IgE/IgG binding capacities. No significant difference on incorporation ratio value of glycated α-LA was observed with and without DHPM pretreatment. However, IgE/IgG binding capacities of α-LA were decreased after glycation and DHPM pretreatment promoted the reduction. The lowest IgE/IgG binding capacities of glycated α-LA were obtained by DHPM pretreatment at 110 MPa. Native α-LA was mainly glycated at K62, K94, K98, whereas glycation sites and degree of substitution per peptide (DSP) were added after DHPM treatment. Therefore, the reduced IgE/IgG binding capacities of α-LA was attributed to the characteristics of glycated sites, including the amount, location, and DSP values. Interestingly, K98 played the most important role in decreasing IgE/IgG binding capacities of α-LA. The study revealed that glycation combined with DHPM was a promising way to decrease the allergenicity of proteins.

Glomerular C4d deposition can precede the development of focal segmental glomerulosclerosis

Recent studies suggest that complement plays a role in the pathogenesis of focal segmental glomerulosclerosis (FSGS). Moreover, co-localization of IgM and C3 deposits with FSGS lesions has frequently been reported. Here, we investigated whether glomerular complement deposition precedes the development of FSGS and whether it represents local complement activation. Renal biopsies from 40 patients with primary FSGS, 84 patients with minimal change disease, and 10 healthy individuals were stained for C4d, C1q, and mannose-binding lectin. C4d deposits were also measured in renal allograft biopsies from 34 patients with native primary FSGS, 18 of whom subsequently developed recurrent FSGS. Lastly, we measured C4d deposits in the Munich Wistar Frömter rat model of FSGS. The prevalence of C4d-positive glomeruli was significantly higher among patients with FSGS (73%) compared to patients with minimal change disease (21%) and healthy individuals (10%). Moreover, segmental sclerosis was absent in 42% of C4d-positive glomeruli. Glomerular C1q was significantly more prevalent in FSGS compared to minimal change disease or healthy individuals, while mannose-binding lectin was infrequently observed. C4d deposition was significantly more prevalent in recurrent FSGS (72%) before the development of sclerotic lesions compared to control transplant samples (27%). Finally, at the onset of albuminuria but before the development of FSGS lesions, Munich Wistar Frömter rats had a significantly higher percentage of C4d-positive glomeruli (31%) compared to control rats (4%). Thus, glomerular C4d deposition can precede the development of FSGS, suggesting that complement activation may play a pathogenic role in the development of FSGS.

Perspectives on diagnostic strategies for hyperglycaemia in pregnancy - Dealing with the barriers and challenges: Europe

Diabetes in pregnancy (DIP) is associated with an increased risk of adverse pregnancy outcomes. Unfortunately guidelines and clinical practices vary significantly and a number of key issues remain under debate. These include: glucose cut-offs for diagnosis; the approaches of universal versus selective screening; appropriate timing of screening; and acceptability of various screening strategies to the population at risk. Economic considerations are also of importance, but unfortunately data outlining the best approach from this viewpoint are limited. In this paper, we review each of these topics and examine associated barriers and challenges associated with various strategies from a European perspective. We also address options which potentially may have a future role in the care of these women including alternative diagnostic biomarkers.