Effect of aspirin on the complement system in vitro

Effects of physiologically relevant dynamic shear stress on platelet complement activation

Disturbed shear stress, commonly found in cardiovascular diseases, plays important roles in platelet activation and functions. It has been reported that when activated by elevated shear stress, platelets were able to support complement activation to completion. In this study, through a dynamic cone and plate shearing device, three physiologically relevant shear stresses were applied to platelets, mimicking the shear conditions when platelets pass through a normal left coronary artery (0.05-1 Pa), a 60% stenosis (elevated shear stress at 6.5 Pa for less than 0.1 s), and when platelets are trapped in a recirculation zone past a stenosis (<0.5 Pa). After shear exposure, platelet-surface complement activation (C1q, C4d, iC3b, and SC5b-9 depositions) was measured using a solid-phase ELISA approach and flow cytometry. Production of complement regulatory proteins - C1-inhibitor (C1-INH) and complement receptor 1 (CR1), was also measured. Results demonstrated that low-pulsatile shear stress (recirculation) was able to initiate platelet complement activation, by increasing C1q deposition significantly. Both pathological shear stresses triggered significant increases in C1 inhibitor generation and noticeable changes in CR1 production, effectively preventing complement activation from completion. These results suggested that for platelets, low-pulsatile shear stress may be more pro-atherogenic, compared to elevated shear stress, especially when the shear stress exposure time is short.

Association analysis of C6 genetic variations and aspirin hypersensitivity in Korean asthmatic patients

There has been increasing evidence that genetic mechanisms contribute to the development of aspirin-intolerant asthma (AIA), a life-threatening disease. The complement component (C6) is a constituent of a biochemical cascade that has been implicated in airway epithelial damage and nasal polyposis, and therefore, may be a risk factor for AIA. To investigate the association between C6 variations and AIA in a Korean asthma cohort, 27 SNPs were selected for genotyping based on previously reported polymorphisms in the HapMap database. Genotyping was carried out using TaqMan assay, and five major haplotypes were obtained in 163 AIA cases and 429 aspirin-tolerant asthma (ATA) controls subjects. Genotype frequency distributions of C6 polymorphisms and haplotypes were analyzed using logistic and regression models. Subsequent analyses revealed a lack of association between C6 genetic variations and AIA. From the initial analyses, marginal associations of rs10512766 (p = 0.04 in co-dominant model) and rs4957374 (p = 0.05 in dominant model) with AIA did not reach the threshold of significance after multiple testing corrections; thus this study failed to find convincing evidence that variations in C6 gene influence the risk of AIA in a Korean population. However, these preliminary results may contribute to the etiology of aspirin hypersensitivity in Korean asthmatic patients.

Complement C3a and C4a increased in plasma of patients with aspirin-induced asthma

RATIONALE

Aspirin-induced asthma (AIA) is a distinct clinical syndrome that affects up to 10% of adults with asthma. Although eicosanoid metabolites appear to play an important role in AIA, the exact pathogenic mechanism for the syndrome remains obscure. In addition, the proposed mechanism fails to explain why aspirin does not cause bronchoconstriction in all individuals.

OBJECTIVES

We aimed to identify proteins that were differentially expressed in between AIA and aspirin-tolerant asthma (ATA) plasma.

METHODS AND MAIN RESULTS

By using a proteomics approach, six proteins were found to be differentially expressed in plasma between patients with AIA and patients with ATA at baseline, and eight proteins were significantly up- or down-regulated after aspirin challenge in patients with AIA. These proteins, which were identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, can be classified into four groups: complement components, apolipoproteins, modified albumin, and unknown proteins. Among them, the complement component levels in plasma were validated by using ELISA. Plasma concentrations of C3a and C4a were higher in patients with AIA (n = 30) than in patients with ATA (n = 24). After the aspirin challenge, C3 decreased in both patients with AIA and those with ATA, but the C3a concentration increased in the AIA patient group (p = 0.019). Moreover, C3a and C4a levels and the ratios of C3a/C3 and C4a/C4 were correlated with the changes of FEV(1) values after aspirin challenge.

CONCLUSIONS

Aspirin intolerance may be related to alterations in the levels of complements, as well as those of lipoprotein and other proteins.

Release of sulfidoleukotrienes in vitro: its relevance in the diagnosis of pseudoallergy to acetylsalicylic acid

Pseudo-allergic reactions (PAR) are caused by a variety of drugs, of particular interest by acetylsalicylic acid (ASA) and other nonsteroidal antiinflammatory drugs. The clinical symptoms often resemble immediate type hypersensitivity reactions and consist of bronchospasm, urticaria, angioedema and even anaphylactic shock. Antigen specific immune mechanisms, however, are not involved. In general, skin tests are not reliable and the diagnosis of PAR is based mainly on risky provocation tests. Therefore, the purpose of this study was to establish procedures for in vitro diagnosis of PAR to ASA. A controlled study was performed including patients with PAR to ASA based on history and positive oral provocation test and non-atopic as well as atopic controls. In this in vitro study the production of sulfidoleukotrienes (sLT) by isolated leukocytes was measured by cellular allergen stimulation test (CAST), which is based on detection of LTC4, LTD4 and LTE4 by a monoclonal antibody. Accordingly, the direct effect of ASA as well as the modulatory effect of ASA on C5a-induced production of sLT in leukocytes in vitro was investigated. In patients with PAR to ASA, C5a-induced generation of sLT was significantly increased as compared to normal controls. In contrast, there was no difference in the spontaneous release of sLT in vitro in patients and controls. Preincubation of leukocytes with ASA did not exert a significant modulatory effect on the spontaneous or the C5a-induced production of sLT in patients and controls. In summary, the present study provides a novel in vitro test system for the diagnosis of PAR to ASA by measurement of sLT release in leukocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a streptococcal lipoteichoic acid on complement activation in vitro

This study describes activation of serum complement by lipoteichoic acid (LTA) from Streptococcus mutans OMZ 176, while in solution. Serum from 16 healthy students was taken. Test samples were incubated with increasing doses (1-5,000 micrograms/ml) of LTA or lipopolysaccharide (LPS) from Escherichia coli 0111:B4 for 1 h at 37 degrees C; then assayed for degradation of C3, C4 or factor B by crossed immunoelectrophoresis. Each preparation caused a significant (p < 0.05) dose-dependent conversion of C3. The response curves obtained were not statistically different. LPS was a stronger activator of the alternative pathway than LTA, as judged from analysis of C3 degradation in the presence of Mg2+/EGTA, and from their effects on factor B cleavage. LTA caused, however, pronounced alterations in the shape of C4 precipitation in the gels. Functional (hemolytic) assays showed that, when tested at 200 micrograms/ml, LTA and LPS triggered significant (p < 0.05) consumptions of both classical and alternative pathway proteins. LPS was a significantly (p < 0.05) stronger activator than LTA. Apparently, the C3 degradation found for this LTA involved the alternative pathway to a small extent; thus some other mechanism of fluid-phase C3 cleavage seemed also to be operative.

[Paroxysmal nocturnal hemoglobinuria]

Paroxysmal nocturnal hemoglobinuria, first described in the late 19th century, is an acquired disorder characterized by hemoglobinemia and hemoglobinuria. The major clinical manifestation of PNH is chronic intravascular hemolysis of various severity. Patients-mostly young adults - may also present with episodes of abdominal or back pain. Common cause of death is thrombosis especially of the hepatic veins. Granulocytopenia and thrombocytopenia may be the initial manifestation of PNH, indicating that the disorder is a primary bone-marrow disease, affecting not only the erythrocytes but also other peripheral blood cells and the haematopoietic stem cell. The course of the disease is variable. Partial complete recovery was described, but also fatal thrombosis. The major phenotypic expression of PNH is an increased susceptibility of the erythrocytes to the lytic action of complement in vitro. The enhanced complement susceptibility is most probably due to membrane defects: two membrane proteins regulating the complement cascade in PNH cells were missing, the decay-accelerating factor, DAF, inhibiting the activation of the lytic complement complex and the C8 binding protein, C8bp, which interferes with the lytic process. Aside from the lack of the complement regulators also other membrane defects have been described (e.g. of acetylcholinesterase or alkaline phosphatase). The proteins as well as DAF and C8bp are linked to the cell membrane via a phosphatidylinositol (PI) anchor, leading to the speculation that the disease results from a deficiency in the post-translational PI anchoring mechanism. The diagnosis of PNH is based on the Hamtest, but will be extended to the quantitation of the above described membrane proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

A review of mechanism of action of aspirin and its potential as an immunomodulating agent

The basic aspects of PG immune function interactions are presented and discussed herein. Specifically, the findings of many of the studies summarized suggest the possibility that pharmacologic actions of aspirin may play a role in enhancing the immune response to viral infections. Mechanisms proposed for ASA include: PG inhibition via the cyclooxygenase pathway, an interaction with cyclic nucleotides, altered cellular interactions with PG's, altered leukocyte migration, activation of complement components, stimulation of monocytopoiesis, and induction of interferon. Since dual effects for ASA have been observed for several of these mechanisms, it is clear that its role in modulating the immune response to viral infections is very complex. This delineation of a role for ASA, that would seem to constitute a defense against viral infections leads to an area worthy of study and surveillance.

The role of complement in inflammation

The inflammatory process may be initiated by a great variety of stimuli. Amongst the diverse pathogenic pathways that lead from the primary stimulus to the tissue response, the serum complement system (C) seems the most important and, certainly, it is the best analyzed of the mediator systems.

Aspirin-sensitive asthma

Aspirin intolerance is particularly common in asthmatic patients who additionally have chronic rhinitis and/or nasal polyps. These individuals differ in several respects from patients who experience urticaria and/or angioedema after aspirin administration, and differing mechanisms may be involved. Data regarding the latter are indirect and incomplete, but suggest that ASA-sensitive asthma is most likely to be related in some manner to the capacity of ASA to inhibit cyclooxygenases, enhanced lipoxygenase metabolism perhaps playing a crucial role. Current research employing ASA "desensitization" may help to elucidate these enigmas.

The absence of detectable complement activation in aspirin-sensitive asthmatic patients during aspirin challenge

Activation of complement was sought by two independent assay methods, total hemolytic complement (CH50) and C4 activation by rocket immunoelectrophoresis for C4d and C4 in plasma samples obtained from 16 aspirin-sensitive asthmatic patients and four control subjects during provocative oral aspirin challenges. No consistent evidence of significant complement activation was detected in either the asthmatic or control groups when serial measurements were performed. The measurements of CH50 and C4 activation did not change in either arterial or venous samples. These findings indicate that oral aspirin given in dosages that provoke bronchospasm did not activate C4 or significantly decrease serum complement activity.