The anti-factor D antibody, MAb 166-32, inhibits the alternative pathway of the human complement system

Praziquantel and factor H recruitment differentially affect the susceptibility of Schistosoma mansoni to complement-mediated damage

Background

Schistosomes are highly efficient evaders of human immunity, as evident by their ability to survive in human blood for years. How they protect themselves against the constant attack by a key element of innate immunity, the complement system, has remained unclear. In this study, new light is shed on the interaction between distinct life-cycle stages of Schistosoma mansoni and the human complement system.

Results

We demonstrate that schistosomula, the young stage assumed immediately after cercaria penetration of the skin, are extremely vulnerable towards complement-mediated killing as only 10-20% survive. The survival rate increases to 70% already within 30 minutes and reaches close to 100% within two hours. Pathway-specific complement inhibitors revealed the alternative pathway of complement activation as the main contributor to killing and damage of the schistosomula. Moreover, the complement regulator factor H is recruited by the schistosomula in this early stage to evade killing. Surviving parasites appear fully viable despite the ongoing complement attack, as demonstrated by the deposition of C3 fragments. However, when exposed to the widely used schistocidal drug praziquantel, the vulnerability of 24 h-old schistosomula towards complement-mediated killing is notably increased; no such effect was observed for mefloquine or oxamniquine. Similar to the younger life-cycle stages, adult worms remain under complement attack. C3 fragments were found all over the outer surface (tegument), deposited mostly on the ridges and not on the tubercles.

Conclusion

The recruitment of factor H merits more detailed studies that pinpoint the molecules involved and elucidate the novel possibilities to intercept the uncovered immune evasion therapeutically. That praziquantel and complement work in synergy is surprising and may in the future result in enhanced understanding of the drug's mechanism of action.

Population Pharmacokinetics and Pharmacodynamics of Lampalizumab Administered Intravitreally to Patients With Geographic Atrophy

Intravitreally administered lampalizumab is an investigational complement inhibitor directed against complement factor D (CFD) for the treatment of geographic atrophy (GA) secondary to age-related macular degeneration. We sought to develop an integrated ocular and systemic pharmacokinetic/pharmacodynamic model for lampalizumab in patients with GA using the data from the clinical phase I and II studies. The kinetics of lampalizumab and CFD disposition were well described by the combined ocular/serum target-mediated drug disposition model using a quasi-steady-state approximation. This model takes into account the drug, target, and drug-target complex clearance, their transfer rates between ocular and serum compartments, and turnover kinetics of CFD. The constructed model provided a prediction of target occupancy in ocular tissues and supported that the two dosing regimens (10 mg q4w and 10 mg q6w) selected for the phase III studies are expected to be efficacious and able to achieve near-complete target engagement in the vitreous humor.

Complement inhibition in cynomolgus monkeys by anti-factor d antigen-binding fragment for the treatment of an advanced form of dry age-related macular degeneration

Anti-factor D (AFD; FCFD4514S, lampalizumab) is a humanized IgG Fab fragment directed against factor D (fD), a rate-limiting serine protease in the alternative complement pathway (AP). Evaluation of AFD as a potential intravitreal (IVT) therapeutic for dry age-related macular degeneration patients with geographic atrophy (GA) is ongoing. However, it is unclear whether IVT administration of AFD can affect systemic AP activation and potentially compromise host-immune responses. We characterized the pharmacologic properties of AFD and assessed the effects of AFD administered IVT (2 or 20 mg) or intravenous (0.2, 2, or 20 mg) on systemic complement activity in cynomolgus monkeys. For the IVT groups, serum AP activity was reduced for the 20 mg dose group between 2 and 6 hours postinjection. For the intravenous groups, AFD inhibited systemic AP activity for periods of time ranging from 5 minutes (0.2 mg group) to 3 hours (20 mg group). Interestingly, the concentrations of total serum fD increased up to 10-fold relative to predose levels following administration of AFD. Furthermore, AFD was found to inhibit systemic AP activity only when the molar concentration of AFD exceeded that of fD. This occurred in cynomolgus monkeys at serum AFD levels ≥2 µg/ml, a concentration 8-fold greater than the maximum serum concentration observed following a single 10 mg IVT dose in a clinical investigation in patients with GA. Based on these findings, the low levels of serum AFD resulting from IVT administration of a clinically relevant dose are not expected to appreciably affect systemic AP activity.

Inhibiting alternative pathway complement activation by targeting the factor D exosite

By virtue of its amplifying property, the alternative complement pathway has been implicated in a number of inflammatory diseases and constitutes an attractive therapeutic target. An anti-factor D Fab fragment (AFD) was generated to inhibit the alternative complement pathway in advanced dry age-related macular degeneration. AFD potently prevented factor D (FD)-mediated proteolytic activation of its macromolecular substrate C3bB, but not proteolysis of a small synthetic substrate, indicating that AFD did not block access of the substrate to the catalytic site. The crystal structures of AFD in complex with human and cynomolgus FD (at 2.4 and 2.3 Å, respectively) revealed the molecular details of the inhibitory mechanism. The structures show that the AFD-binding site includes surface loops of FD that form part of the FD exosite. Thus, AFD inhibits FD proteolytic function by interfering with macromolecular substrate access rather than by inhibiting FD catalysis, providing the molecular basis of AFD-mediated inhibition of a rate-limiting step in the alternative complement pathway.

The Pathway-Selective Estrogen Receptor Ligand WAY-169916 Reduces Infarct Size After Myocardial Ischemia and Reperfusion by an Estrogen Receptor Dependent Mechanism

Previous studies have shown that estrogen treatment protects the heart from reperfusion injury. The adverse effects of long-term estrogen treatment limit its clinical use and emphasize the need for the development of specific pharmacological interventions such as pathway-selective estrogen receptor (ER) ligands. Pathway-selective ER ligands are compounds that retain estrogen's anti-inflammatory ability, but they are devoid of conventional estrogenic action. In the present study, the pathway-selective ER ligand WAY-169916 was assessed for its cardioprotective potential in an in vivo model of ischemia-reperfusion injury. Anesthetized, ovariectomized rabbits were administered WAY-169916 (1 mg/kg), 17beta-estradiol (E2; 20 microg/rabbit), or vehicle intravenously 30 minutes before a 30-minute occlusion and 4 hours of reperfusion. Acute treatment with either WAY-169916 or E2 resulted in a decrease in infarct size, expressed as a percent of area at risk (WAY-169916, 21.2 +/- 3.3; P < 0.001 and E2, 18.8 +/- 1.7; P < 0.001) compared with vehicle 59.4 +/- 5.4). Pretreatment with estrogen receptor antagonist ICI 182,780 significantly limited the infarct size sparing effect of both WAY-169916 and E2 when expressed as a percent of the risk region (WAY 169916, 47.4 +/- 4.4; E2, 53.01 +/- 5.0). The results demonstrate that WAY-169916 protects the heart against ischemia-reperfusion injury through an ER-dependent mechanism.

The role of complement C3 opsonization, C5a receptor, and CD14 in E. coli-induced up-regulation of granulocyte and monocyte CD11b/CD18 (CR3), phagocytosis, and oxidative burst in human whole blood

The relative role of complement and CD14 in Escherichia coli-induced leukocyte CD11b up-regulation, phagocytosis, and oxidative burst in human whole blood was examined. The highly specific thrombin inhibitor lepirudin was used as anticoagulant, as it does not affect complement activation. Complement inhibition at the level of C3 (anti-C2 and anti-factor D) and C5 (C5a receptor antagonist and anti-C5/C5a) efficiently inhibited CD11b up-regulation, phagocytosis, and oxidative burst in granulocytes. Monocyte activation was generally less complement-dependent, but when C3 activation was blocked, a pronounced inhibition of phagocytosis and oxidative burst was obtained. Only the combination of anti-C2 and antifactor D blocked E. coli C3 opsonization completely. Whole E. coli, disrupted E. coli, and the C3-convertase activator cobra venom factor up-regulated CD11b rapidly on both cell types, proportional to their complement activation potential in the fluid phase. In comparison, purified LPS at concentrations comparable with that present in the E. coli preparations did not activate complement. Oxidative burst was induced only by whole bacteria. Finally, the combination of complement inhibition and anti-CD14 completely blocked E. coli-induced granulocyte and monocyte CD11b up-regulation and quantitatively, virtually abolished phagocytosis. The results indicate that complement and CD14, despite differential effects on granulocytes and monocytes, are the two crucial, quantitative factors responsible for E. coli-induced CD11b, phagocytosis, and oxidative burst in both cell types.

Strategies of therapeutic complement inhibition

The involvement of complement in the pathogenesis of a great number of partly life threatening diseases defines the importance to develop inhibitors which specifically interfere with its deleterious action. Endogenous soluble complement-inhibitors, antibodies or low molecular weight antagonists, either blocking key proteins of the cascade reaction or neutralizing the action of the complement-derived anaphylatoxins have successfully been tested in various animal models over the past years. Promising results consequently led to first clinical trials. This review is focused on different approaches for the development of inhibitors, on their site of action in the cascade, on possible indications for complement inhibition based on experimental animal data, and on potential side effects of such treatment.

Activation of estrogen receptor-alpha protects the in vivo rabbit heart from ischemia-reperfusion injury

The estrogen receptor (ER) mediates estrogenic activity in a variety of organs, including those in the reproductive, cardiovascular, immune, and central nervous systems. Experimental studies have demonstrated that 17beta-estradiol (E2) protects the heart from ischemia-reperfusion injury. Two estrogen receptors, ER alpha and ER beta, mediate the actions of estrogen; however, it is not certain which ER mediates the cardioprotective effects of E2. In the present study, the ER-selective agonists 4,4',4''-[4-propyl-(1H)-pyrazole-1,3,5-triyl]tris-phenol (PPT; ER alpha) and 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN; ER beta) were assessed for their cardioprotective potential in an in vivo rabbit model of ischemia-reperfusion injury. Anesthetized female rabbits were administered PPT (3 mg/kg), DPN (3 mg/kg), E2 (20 microg/rabbit), or vehicle intravenously 30 min before a 30-min occlusion of the left anterior descending coronary artery followed by 4 h of reperfusion. Acute treatment with E2 (17.7 +/- 2.9%; P < 0.001) and PPT (18.1 +/- 2.9%; P < 0.001), but not DPN (45.3 +/- 2.4%) significantly decreased infarct size as a percent of area at risk compared with vehicle (45.3 +/- 2.4%). Coadministration of PPT or E2 with the ER antagonist ICI-182,780 limited the infarct size-sparing effect of the compounds (43.8 +/- 6.6% and 40.6 +/- 5.7% respectively, expressed as a percentage of risk region). PPT reduced the release of cardiac-specific troponin-I and reduced the tissue deposition of the membrane attack complex and C-reactive protein similar to that of E2. The results indicate that activation of ER alpha, but not ER beta, is required for the observed cardioprotective effects of E2.

Effects of complement factor D deficiency on the renal disease of MRL/lpr mice

BACKGROUND

The alternative complement pathway (AP) is activated in individuals with lupus nephritis and in murine models of systemic lupus erythematosus, including MRL/lpr mice. A previous study from our laboratory evaluated the development of renal disease in MRL/lpr mice genetically deficient in factor B (Bf-/-), a protein necessary for AP activation. MRL/lpr Bf-/- mice developed less renal disease and had improved survival; however, these mice were also a different major histocompatibility complex (MHC) haplotype (H-2b) than their wild-type littermates (H-2k) due to the gene for Bf being located in the MHC gene complex. We undertook the current study to determine if the decreased renal disease in MRL/lpr Bf-/- mice was due to the lack of AP activation or the H-2b haplotype by studying the effects of factor D (Df) deficiency, a critical protein for AP activation, on disease development in MRL/lpr mice.

METHODS

Df-deficient mice were backcrossed with MRL/lpr mice for four to nine generations. MRL/lpr H-2k Df-/-, Df+/-, and Df+/+ littermates were evaluated for disease development. Lack of AP activation in MRL/lpr Df-/- mice was determined by the zymosan assay. Serum creatinine levels were measured using a creatinine kit. Proteinuria and autoantibody levels were determined by enzyme-linked immunosorbent assay (ELISA). Sections from one kidney were stained with fluorescein isothiocyanate (FITC) alpha-murine C3 or alpha-murine IgG to detect C3 and IgG deposition. The remaining kidney was cut in half with one half fixed, sectioned, and stained with hematoxylin and eosin and periodic acid-Schiff (PAS) to evaluate pathology and another half fixed in glutaraldehyde and examined via electron microscopy.

RESULTS

MRL/lpr Df-/- mice had similar glomerular IgG deposition, proteinuria and autoantibody levels, as Df+/+ and Df+/- littermates. However, glomerular C3 deposition, serum creatinine levels, and pathologic renal disease were significantly reduced in Df-/- mice. Despite the lack of renal disease in Df-/- mice, life span was not impacted by factor D deficiency.

CONCLUSION

The absence of Df and AP activation is protective against the development of proliferative renal disease in MRL/lpr mice suggesting the similar effect of Bf deficiency in MRL/lpr mice was also due to the lack of AP activation.

Microvascular Inflammatory Response in Cardiac Surgery

Cardiac surgical procedures, with or without cardiopulmonary bypass, elicit a systemic inflammatory response in patients that induces the elaboration of multiple cytokines, chemokines, adhesion molecules, and destructive enzymes. This inflammatory reaction involves multiple interdependent and redundant cell types and humoral cascades, which allows for amplification and positive feedback at numerous steps. This systemic inflammatory response ultimately results in a broad spectrum of clinical manifestations, with multiple organ failure being the most severe form. Investigative efforts have focused on understanding the mechanism of this systemic inflammatory response syndrome in order to develop potential therapeutic targets to inhibit it, thereby possibly decreasing postoperative morbidity and mortality. Multiple therapeutic methods have been investigated, including pharmacologic inhibitors and modifications of surgical technique and the cardiopulmonary bypass circuit. Although studies have demonstrated that the use of these therapies in experimental and clinical settings has attenuated the systemic inflammatory response, they have failed to conclusively show clinical benefit from these therapies. These therapies may be too specific to minimize the deleterious effects of a systemic inflammatory response that results from the activation of multiple, interdependent, and redundant inflammatory cascades and cell types. Hence, further studies that investigate the molecular and cellular events underlying the systemic inflammatory response syndrome and the resultant effects of anti-inflammatory therapies are warranted to ultimately achieve improvements in clinical outcome after cardiac surgical procedures.

Role for the alternative complement pathway in ischemia/reperfusion injury

The terminal complement components play an important role in mediating tissue injury after ischemia and reperfusion (I/R) injury in rats and mice. However, the specific complement pathways involved in I/R injury are unknown. The role of the alternative pathway in I/R injury may be particularly important, as it amplifies complement activation and deposition. In this study, the role of the alternative pathway in I/R injury was evaluated using factor D-deficient (-/-) and heterozygote (+/-) mice. Gastrointestinal ischemia (GI) was induced by clamping the mesenteric artery for 20 minutes and then reperfused for 3 hours. Sham-operated control mice (+/- versus -/-) had similar baseline intestinal lactate dehydrogenase activity (P = ns). Intestinal lactate dehydrogenase activity was greater in -/- mice compared to +/- mice after GI/R (P = 0.02) thus demonstrating protection in the -/- mice. Intestinal myeloperoxidase activity in +/- mice was significantly greater than -/- mice after GI/R (P < 0.001). Pulmonary myeloperoxidase activity after GI/R was significantly higher in +/- than -/- mice (P = 0.03). Addition of human factor D to -/- animals restored GI/R injury and was prevented by a functionally inhibitory antibody against human factor D. These data suggest that the alternative complement pathway plays an important role in local and remote tissue injury after GI/R. Inhibition of factor D may represent an effective therapeutic approach for GI/R injury.

Role for the alternative complement pathway in ischemia/reperfusion injury

The terminal complement components play an important role in mediating tissue injury after ischemia and reperfusion (I/R) injury in rats and mice. However, the specific complement pathways involved in I/R injury are unknown. The role of the alternative pathway in I/R injury may be particularly important, as it amplifies complement activation and deposition. In this study, the role of the alternative pathway in I/R injury was evaluated using factor D-deficient (-/-) and heterozygote (+/-) mice. Gastrointestinal ischemia (GI) was induced by clamping the mesenteric artery for 20 minutes and then reperfused for 3 hours. Sham-operated control mice (+/- versus -/-) had similar baseline intestinal lactate dehydrogenase activity (P = ns). Intestinal lactate dehydrogenase activity was greater in -/- mice compared to +/- mice after GI/R (P = 0.02) thus demonstrating protection in the -/- mice. Intestinal myeloperoxidase activity in +/- mice was significantly greater than -/- mice after GI/R (P < 0.001). Pulmonary myeloperoxidase activity after GI/R was significantly higher in +/- than -/- mice (P = 0.03). Addition of human factor D to -/- animals restored GI/R injury and was prevented by a functionally inhibitory antibody against human factor D. These data suggest that the alternative complement pathway plays an important role in local and remote tissue injury after GI/R. Inhibition of factor D may represent an effective therapeutic approach for GI/R injury.

Human serum-induced expression of E-selectin on porcine aortic endothelial cells in vitro is totally complement mediated

BACKGROUND

Whereas complement is a key mediator of hyperacute xenograft rejection, its role in acute vascular rejection (AVR) is a matter of controversy. AVR is associated with de novo synthesis of endothelial cell-derived inflammatory mediators, including the leukocyte-recruiting adhesion molecule E-selectin. Here we investigate the role and mechanism of complement in human serum-induced porcine endothelial cell activation.

METHODS

An in vitro xenotransplantation method was designed using porcine aortic endothelial cells stimulated with human serum in microculture wells. E-selectin expression was measured by cell-enzyme immunoassay. Complement inhibitors acting at different levels in the cascade were investigated for their effect on E-selectin expression.

RESULTS

E-selectin was strongly induced by normal human serum but not by heat-inactivated serum. Compstatin, a synthetic C3 inhibitor, markedly reduced human serum-induced E-selectin expression. Purified C1-inhibitor suppressed E-selectin induction completely, indicating activation through the classical or lectin pathway. Furthermore, a monoclonal antibody (mAb) that inhibits cleavage of C5 or another mAb that blocks the function of C7, completely inhibited the expression of serum-induced E-selectin, consistent with the terminal C5b-9 complement complex being the mediator of the endothelial cell activation. Inhibition of the alternative pathway using a novel antifactor D mAb did not reduce E-selectin expression.

CONCLUSION

Human serum-induced expression of porcine E-selectin is totally complement dependent, induced by a C1-inhibitor regulated pathway and mediated through the terminal complement complex. The data may have implications for therapeutic strategies, particularly of C1-inhibitor and anti-C5 mAb, to protect against endothelial cell activation and subsequent AVR of porcine xenografts.

Inhibition of complement, neutrophil, and platelet activation by an anti-factor D monoclonal antibody in simulated cardiopulmonary bypass circuits

OBJECTIVES

Patients undergoing cardiopulmonary bypass frequently manifest generalized systemic inflammation and occasionally manifest serious multiorgan failure. Inflammatory responses of bypass are triggered by contact of blood with artificial surfaces of the bypass circuits, surgical trauma, and ischemia-reperfusion injury. We studied the effects of specific inhibition of the alternative complement cascade by using an anti-factor D monoclonal antibody (166-32) in extracorporeal circulation of human whole blood used as a simulated model of cardiopulmonary bypass.

METHODS

Five healthy blood donors were used in the study. Monoclonal antibody 166-32 was added to freshly collected, heparinized human blood recirculated in a pediatric cardiopulmonary bypass circuit at a final concentration of 18 microg/mL. An irrelevant monoclonal antibody was used as a negative control with the same donor blood in a parallel bypass circuit on the same day. Blood samples were collected at different time points during recirculation for measurement of activation of complement, neutrophils, and platelets by immunofluorocytometric methods and enzyme-linked immunosorbent assays.

RESULTS

Monoclonal antibody 166-32 inhibited the alternative complement activation and the production of Bb, C3a, sC5b-9, and C5a. Upregulation of CD11b on neutrophils and CD62P on platelets was also significantly inhibited by monoclonal antibody 166-32. This is consistent with the inhibition of the release of neutrophil-specific myeloperoxidase and elastase and platelet thrombospondin. The production of proinflammatory cytokine interleukin 8 was also suppressed by the antibody.

CONCLUSIONS

The alternative complement cascade is predominantly activated during extracorporeal circulation. Anti-factor D monoclonal antibody 166-32 is effective in inhibiting the activation of complement, neutrophils, and platelets. Inhibition of the alternative complement pathway by targeting factor D could be useful in reducing systemic inflammation in patients undergoing cardiopulmonary bypass.