Identification of C3a and N-truncated C3a as vascular permeability-enhancing factors from the exudate of chronic phase of carrageenan-induced inflammation in rats

The role of complement membrane attack complex in dry and wet AMD - From hypothesis to clinical trials

Data from human dry and wet age-related macular degeneration (AMD) eyes support the hypothesis that constant 'tickover' of the alternative complement pathway results in chronic deposition of the complement membrane attack complex (MAC) on the choriocapillaris and the retinal pigment epithelium (RPE). Sub-lytic levels of MAC lead to cell signaling associated with tissue remodeling and the production of cytokines and inflammatory molecules. Lytic levels of MAC lead to cell death. CD59 is a naturally occurring inhibitor of the assembly of MAC. CD59 may thus be therapeutically efficacious against the pathophysiology of dry and wet AMD. The first gene therapy clinical trial for geographic atrophy - the advanced form of dry AMD has recently completed recruitment. This trial is studying the safety and tolerability of expressing CD59 from an adeno-associated virus (AAV) vector injected once into the vitreous. A second clinical trial assessing the efficacy of CD59 in wet AMD patients is also under way. Herein, the evidence for the role of MAC in the pathophysiology of dry as well as wet AMD and the scientific rationale underlying the use of AAV- delivered CD59 for the treatment of dry and wet AMD is discussed.

Imaging of carrageenan-induced local inflammation and adjuvant-induced systemic arthritis with [(11)C]PBR28 PET

INTRODUCTION

[(11)C] PBR28 binding to translocator protein (TSPO) was evaluated for imaging of acute and chronic inflammation using two established rat models.

METHODS

Acute inflammation was induced by local carrageenan injection into the paw of Fisher 344 rats (model A). T-cell mediated adjuvant arthritis was induced by heat-inactivated Mycobacterium butyricum injection in Lewis rats (model B). Micro-PET scan was performed after injection of approximately 35 MBq [(11)C]PBR28. In model A, volumes of interest (VOIs) were defined in the paw of Fisher 344 rats (n=6) with contralateral sham treatment as control. For model B, VOIs were defined in the tail, sacroiliac joints, hips, knees and thigh muscles of M. butyricum treated animals (n=8) and compared with sham-treated controls (n=4). The peak (11)C-PBR28 SUV (SUVpeak) and area under the curve (AUCSUV) of 60-minute time-activity data were calculated. Immunohistochemistry for CD68, a macrophage stain, was performed from paw tissues. In addition, the [(11)C]PBR28 cell uptake was measured in lipopolysaccharide (LPS)-stimulated and non-stimulated macrophage cultures.

RESULTS

LPS-stimulated macrophages displayed dose-dependent increased [(11)C]PBR28 uptake, which was blocked by non-labeled PBR28. In both models, radiotracer uptake of treated lesions increased rapidly within minutes and displayed overall accumulative kinetics. The SUVpeak and AUCSUV of carrageenan-treated paws was significantly increased compared to controls. Also, the [(11)C]PBR28 uptake ratio of carrageenan-treated vs. sham-treated paw correlated significantly with CD68 staining ratios of the same animals. In adjuvant arthritis, significantly increased [(11)C]PBR28 SUVpeak and AUCSUV values were identified at the tail, knees, and sacroiliac joints, while no significant differences were identified in the lumbar spine and hips.

CONCLUSIONS

Based on our initial data, [(11)C]PBR28 PET appears to have potential for imaging of various inflammatory processes involving macrophage activation.

Fasitibant chloride, a kinin B₂ receptor antagonist, and dexamethasone interact to inhibit carrageenan-induced inflammatory arthritis in rats

BACKGROUND AND PURPOSE

Bradykinin, through the kinin B₂ receptor, is involved in inflammatory processes related to arthropathies. B₂ receptor antagonists inhibited carrageenan-induced arthritis in rats in synergy with anti-inflammatory steroids. The mechanism(s) underlying this drug interaction was investigated.

EXPERIMENTAL APPROACH

Drugs inhibiting inflammatory mediators released by carrageenan were injected, alone or in combination, into the knee joint of pentobarbital anaesthetized rats 30 min before intra-articular administration of carrageenan. Their effects on the carrageenan-induced inflammatory responses (joint pain, oedema and neutrophil recruitment) and release of inflammatory mediators (prostaglandins, IL-1β, IL-6 and the chemokine GRO/CINC-1), were assessed after 6 h.

KEY RESULTS

The combination of fasitibant chloride (MEN16132) and dexamethasone was more effective than each drug administered alone in inhibiting knee joint inflammation and release of inflammatory mediators. Fasitibant chloride, MK571, atenolol, des-Arg⁹-[Leu⁸]-bradykinin (B₂ receptor, leukotriene, catecholamine and B₁ receptor antagonists, respectively) and dexketoprofen (COX inhibitor), reduced joint pain and, except for the latter, also diminished joint oedema. A combination of drugs inhibiting joint pain (fasitibant chloride, des-Arg⁹-[Leu⁸]-bradykinin, dexketoprofen, MK571 and atenolol) and oedema (fasitibant chloride, des-Arg⁹-[Leu⁸]-bradykinin, MK571 and atenolol) abolished the respective inflammatory response, producing inhibition comparable with that achieved with the combination of fasitibant chloride and dexamethasone. MK571 alone was able to block neutrophil recruitment.

CONCLUSIONS AND IMPLICATIONS

Bradykinin-mediated inflammatory responses to intra-articular carrageenan were not controlled by steroids, which were not capable of preventing bradykinin effects either by direct activation of the B₂ receptor, or through the indirect effects mediated by release of eicosanoids and cytokines.

Cross-talk between the complement and the kinin system in vascular permeability

The endothelium is a continuous physical barrier that regulates coagulation and selective passage of soluble molecules and circulating cells through the vessel wall into the tissue. Due to its anatomic localization, the endothelium may establish contact with components of the complement, the kinin and the coagulation systems which are the main, though not exclusive, inducers of vascular leakage. Although the complement and the kinin systems may act independently, increasing evidence suggest that there is a crosstalk that involve different components of both systems. Activation is required for the function of the two systems which are involved in pathological conditions such as hereditary and acquired angioedema (AE) and vasculitidis. The aim of this review is to discuss the contribution of complement and kinin systems to vascular leakage and the cross-talk between the two systems in the development of AE. This clinical condition is characterized by episodic and recurrent local edema of subcutaneous and submucosal tissues and is due to inherited or acquired C1-INH deficiency. Although the pathogenesis of the swelling in patients with AE was originally thought to be mediated by C2, ample evidence indicate bradykinin (BK) as the most effective mediator even though the possibility that both the complement and the kinin-forming systems may contribute to the edema has not been completely excluded. BK induces endothelial leakage interacting with B2 receptors but other molecules may be involved in the onset and maintenance of AE. In this review we shall discuss the role of B1 receptors and gC1qR/p33 in addition to that of B2 receptors in the onset of AE attacks and the importance of these receptors as new possible molecular targets for therapy.