Increased Inhibitory Capacity of an Anti-C5a Complementary Peptide Following Acetylation of N-terminal Alanine

The anaphylatoxin C5a: Structure, function, signaling, physiology, disease, and therapeutics

The complement system is one of the oldest known tightly regulated host defense systems evolved for efficiently functioning cell-based immune systems and antibodies. Essentially, the complement system acts as a pivot between the innate and adaptive arms of the immune system. The complement system collectively represents a cocktail of ∼50 cell-bound/soluble glycoproteins directly involved in controlling infection and inflammation. Activation of the complement cascade generates complement fragments like C3a, C4a, and C5a as anaphylatoxins. C5a is the most potent proinflammatory anaphylatoxin, which is involved in inflammatory signaling in a myriad of tissues. This review provides a comprehensive overview of human C5a in the context of its structure and signaling under several pathophysiological conditions, including the current and future therapeutic applications targeting C5a.

Anti-C5a complementary peptide mitigates zymosan-induced severe peritonitis with fibrotic encapsulation in rats pretreated with methylglyoxal

In a previous study of fungal peritoneal injury in peritoneal dialysis patients, complement (C)-dependent pathological changes were developed in zymosan (Zy)-induced peritonitis by peritoneal scraping. However, the injuries were limited to the parietal peritoneum and did not show any fibrous encapsulation of the visceral peritoneum, which differs from human encapsular peritoneal sclerosis (EPS). We investigated peritoneal injury in a rat model of Zy-induced peritonitis pretreated with methylglyoxal (MGO) instead of scraping (Zy/MGO peritonitis) to clarify the role of C in the process of fibrous encapsulation of the visceral peritoneum. Therapeutic effects of an anti-C5a complementary peptide, AcPepA, on peritonitis were also studied. In Zy/MGO peritonitis, peritoneal thickness, fibrin exudation, accumulation of inflammatory cells, and deposition of C3b and C5b-9 with loss of membrane C regulators were increased along the peritoneum until day 5. On day 14, fibrous encapsulation of the visceral peritoneum was observed, resembling human EPS. Peritoneal injuries and fibrous changes were significantly improved with AcPepA treatment, even when AcPepA was administered following injection of Zy in Zy/MGO peritonitis. The data show that C5a might play a role in the development of encapsulation-like changes in the visceral peritoneum in Zy/MGO peritonitis. AcPepA might have therapeutic effects in fungal infection-induced peritoneal injury by preventing subsequent development of peritoneal encapsulation.

C5a inhibitor protects against ischemia/reperfusion injury in rat small intestine

Acute mesenteric ischemia (AMI) is caused by considerable intestinal injury, which is associated with intestinal ischemia followed by reperfusion. To elucidate the mechanisms of ischemia/reperfusion injuries, a C5a inhibitory peptide termed AcPepA was used to examine the role of C5a anaphylatoxin, induction of inflammatory cells, and cell proliferation of the intestinal epithelial cells in an experimental AMI model. In this rat model, the superior mesenteric artery was occluded and subsequently reperfused (Induce‐I/R). Other groups were treated with AcPepA before ischemia or reperfusion. Induce‐I/R induced injuries in the intestine and AcPepA significantly decreased the proportion of severely injured villi. Induce‐I/R induced secondary receptor for C5a‐positive polymorphonuclear leukocytes in the vessels and CD204‐positive macrophages near the injured site; this was correlated with hypoxia‐induced factor 1‐alpha‐positive cells. Induction of these inflammatory cells was attenuated by AcPepA. In addition, AcPepA increased proliferation of epithelial cells in the villi, possibly preventing further damage. Therefore, Induce‐I/R activates C5a followed by the accumulation of polymorphonuclear leukocyte and hypoxia‐induced factor 1‐alpha‐producing macrophages, leading to villus injury. AcPepA, a C5a inhibitory peptide, blocks the deleterious effects of C5a, indicating it has a therapeutic effect on the inflammatory consequences of experimental AMI.

Complement C5A antagonist treatment improves the acute circulatory and inflammatory consequences of experimental cardiac tamponade

OBJECTIVE

Cardiogenic shock often leads to splanchnic macro- and microcirculatory complications, and these events are linked to local and systemic inflammatory activation. Our aim was to investigate the consequences of complement C5a antagonist treatment on the early circulatory and inflammatory changes in a clinically relevant large animal model of cardiac tamponade.

DESIGN AND SETTING

A randomized, controlled in vivo animal study in a university research laboratory.

SUBJECTS

Anesthetized, ventilated, and thoracotomized Vietnamese mini pigs (24 ± 3 kg).

INTERVENTIONS

Group 1 (n = 6) served as sham-operated control. In group 2 (n = 7), cardiac tamponade was induced for 60 minutes by the administration of intrapericardial fluid, while the mean arterial pressure was kept in the interval 40 to 45 mm Hg. Group 3 (n = 6) was treated with a complement C5a antagonist compound (the peptide acetyl-peptide-A, 4 mg/kg) after 45 minutes of tamponade.

MEASUREMENTS AND MAIN RESULTS

The macrohemodynamics, including the superior mesenteric artery flow, was monitored; the average red blood cell velocity in the small intestinal mucosa was determined by an intravital orthogonal polarization imaging technique. The whole blood superoxide production, the plasma level of high-mobility group box protein-1 and big-endothelin and the small intestinal myeloperoxidase activity were measured. One hundred eighty minutes after the relief of tamponade, the mean arterial pressure was decreased, while the plasma levels of superoxide, high-mobility group box protein-1, and big-endothelin, and the intestinal myeloperoxidase activity were increased. The administration of acetyl-peptide-A normalized the mean arterial pressure and preserved the cardiac output, while the superior mesenteric artery flow and mucosal average red blood cell velocity were increased significantly, and the plasma superoxide, high-mobility group box protein-1, big-endothelin, and intestinal myeloperoxidase levels were reduced.

CONCLUSIONS

These results provide evidence that blockade of the C5a effects significantly influences the acute splanchnic macro- and microhemodynamic complications and decreases the potentially harmful inflammatory consequences of experimental cardiogenic shock.

Anti-C5a complementary peptide ameliorates acute peritoneal injury induced by neutralization of Crry and CD59

In peritoneal dialysis (PD) therapy, physical stresses such as exposure to peritoneal dialysate, catheter trauma, and peritonitis may induce peritoneal injury that can prevent continued long-term PD therapy. Therefore, protection of the peritoneum is an important target to enable long-term PD therapy in patients with end-stage renal disease. We previously showed that neutralization of the membrane complement regulators (CRegs) Crry and CD59 in rat peritoneum provokes development of acute peritoneal injury due to uncontrolled complement activation. C5a is a key effecter molecule of the complement system released during acute inflammation. Control of C5a has been proposed as a strategy to suppress inflammatory reactions and, because peritoneal injury is accompanied by inflammation, we hypothesized that C5a targeted therapy might be an effective way to suppress peritoneal injury. In the present study we used an established acute peritonitis model induced by neutralization of CRegs to investigate the effects on acute peritoneal injury of inhibiting C5a. Intravenous administration of an anti-C5a complementary peptide (AcPepA) up to 4 h after induction of injury significantly and dose-dependently prevented accumulation of inflammatory cells and reduced tissue damage in the model, accompanied by decreased C3b deposition. We show that C5a contributed to the development of peritoneal injury. Our results suggest that C5a is a target for preventing or treating peritoneal injury in patients undergoing prolonged PD therapy or with infectious complications.

Inhibiting the C5-C5a receptor axis

Activation of the complement system is a major pathogenic event that drives various inflammatory responses in numerous diseases. All pathways of complement activation lead to cleavage of the C5 molecule generating the anaphylatoxin C5a and, C5b that subsequently forms the terminal complement complex (C5b-9). C5a exerts a predominant pro-inflammatory activity through interactions with the classical G-protein coupled receptor C5aR (CD88) as well as with the non-G protein coupled receptor C5L2 (GPR77), expressed on various immune and non-immune cells. C5b-9 causes cytolysis through the formation of the membrane attack complex (MAC), and sub-lytic MAC and soluble C5b-9 also possess a multitude of non-cytolytic immune functions. These two complement effectors, C5a and C5b-9, generated from C5 cleavage, are key components of the complement system responsible for propagating and/or initiating pathology in different diseases, including paroxysmal nocturnal hemoglobinuria, rheumatoid arthritis, ischemia-reperfusion injuries and neurodegenerative diseases. Thus, the C5-C5a receptor axis represents an attractive target for drug development. This review provides a comprehensive analysis of different methods of inhibiting the generation of C5a and C5b-9 as well as the signalling cascade of C5a via its receptors. These include the inhibition of C5 cleavage through targeting of C5 convertases or via the C5 molecule itself, as well as blocking the activity of C5a by neutralizing antibodies and pharmacological inhibitors, or by targeting C5a receptors per se. Examples of drugs and naturally occurring compounds used are discussed in relation to disease models and clinical trials. To date, only one such compound has thus far made it to clinical medicine: the anti-C5 antibody eculizumab, for treating paroxysmal nocturnal hemoglobinuria. However, a number of drug candidates are rapidly emerging that are currently in early-phase clinical trials. The C5-C5a axis as a target for drug development is highly promising for the treatment of currently intractable major human diseases.

Attenuation of cross-talk between the complement and coagulation cascades by C5a blockade improves early outcomes after intraportal islet transplantation

BACKGROUND

Complement 5a factor (C5a) elicits a broad range of proinflammatory effects, including chemotaxis of inflammatory cells and cytokine release. C5a is also linked to the coagulant activity in autoimmune diseases. Therefore, C5a most likely plays a crucial role in the instant blood-mediated inflammatory reaction.

METHODS

Intraportal transplantation of 2.5 islet equivalents/g of syngeneic rat islet grafts was performed in two groups of streptozotocin-induced diabetic rats: controls and C5a inhibitory peptide (C5aIP)-treated group.

RESULTS

The thrombin-antithrombin complex was significantly suppressed in the C5aIP group (P=0.003), and both the curative rate and the glucose tolerance were significantly improved in the C5aIP group (P<0.05 and P<0.005, respectively). Expression of tissue factor on granulocytes in recipient livers was up-regulated 1 h after islet infusion (P<0.0001), which was significantly suppressed by C5aIP (P<0.005). However, C5aIP was unable to regulate tissue factor expression on isolated islets. Furthermore, no differences were detected between the groups, regarding infiltration of CD11b-positive cells and deposition of C5b-9 on the islet grafts.

CONCLUSIONS

These data suggest that C5aIP attenuates cross-talk between the complement and coagulation cascades through suppressing up-regulation of tissue factor expression on leukocytes in recipient livers but not on islet grafts, a process leading to improvement in islet engraftment. Therefore, C5aIP in combination with conventional anticoagulants could be a strong candidate strategy to control the instant blood-mediated inflammatory reaction induced in clinical islet transplantation.

[Coronary arteritis induced by CAWS (Candida albicans water-soluble fraction) in various strains of mice]

The intraperitoneal administration of CAWS (water-soluble extracellular polysaccharide fraction obtained from the culture supernatant of Candida albicans NBRC 1385) to mice induces coronaritis similar to Kawasaki disease. We analyzed differences in the occurrence of coronary arteritis among mouse strains, inbred strains, a closed colony, hybrids and mutants. CAWS vasculitis was induced in almost all of the inbred and closed colony strains tested, except for CBA / J mice; it was induced also in hybrids, CDF1 and BDF1. In mutant strains of various immunological defects, such as C57BL / 6J Ham Slc-bg , Balb / c nu / nu , C.B.17 / Icr-scid / scid , WBB6F1-W / W (v) mice, all induced CAWS vasculitis but a relatively weak phenotype. It has already been postulated that CAWS vasculitis is regulated by various genes, those related to acute as well as chronic inflammation. This might well reflect the clinical situation in human disease.