Diminished superoxide production of synovial fluid neutrophils in patients with rheumatoid arthritis following piroxicam treatment

Do non-steroidal anti-inflammatory drugs influence chronic inflammation? The effects of piroxicam on chronic antigen-induced arthritis in rats

OBJECTIVE

The effects of non-steroidal anti-inflammatory drugs (NSAIDs) on acute inflammation have been thoroughly investigated. NSAIDs are, however, also prescribed for patients with chronic inflammation, such as rheumatoid arthritis (RA), and objective improvement suggestive of anti-inflammatory action from NSAIDs has not been convincingly shown in chronic RA. An antigen-induced arthritis (AIA) model was used to investigate the effects of piroxicam on chronic inflammation.

METHODS

AIA was induced by injecting methylated bovine serum albumin (mBSA) into the knee joints of previously immunized rats that were treated orally with the NSAID piroxicam or with saline. This treatment was started either before AIA was induced or after it had reached a chronic phase. The findings were recorded by clinical and histological assessment of the joints.

RESULTS

The piroxicam group developed significantly less acute and subsequent chronic knee joint inflammation but this was only evident if the drug was administered prior to the intra-articular mBSA injections. Piroxicam treatment that was initiated during the chronic inflammation did not have any clinical effect, whereas short-term corticosteroid treatment abolished the chronic inflammation. Moreover, histological analysis of the chronic inflammation revealed significantly more inflammatory changes in the piroxicam group compared with the control group.

CONCLUSIONS

Piroxicam treatment had no beneficial effects on the chronic stable inflammation in this model and might even delay histological resolution. As the anti-inflammatory effect of piroxicam is restricted to acute inflammation, the use of NSAIDs during periods of chronic stable arthritis in humans, such as in RA, may need to be investigated.

Phenotypic changes in neutrophils related to anti-inflammatory therapy

Previous work from the group has shown that non-steroidal anti-inflammatory agents given to volunteers and patients inhibit PMN function possibly by affecting the developing neutrophil during the differentiation process. In this study indomethacin treatment in vivo reduced neutrophil chemotaxis and proteolytic degradation of fibronectin, with a maximal effect after 14 days. Stimulated neutrophil adherence to fibronectin was also reduced but this was not due to quantitative changes in beta(2) integrin expression or function. L-Selectin expression on resting and stimulated neutrophils was increased after 14 days and there was a small decrease in plasma levels of soluble L-selectin. These effects, however, could not be reproduced by treatment of neutrophils with indomethacin in vitro, suggesting they are due to effects on differentiating/maturing PMNs. In an attempt to interpret these changes, studies were performed with dexamethasone, which is known to alter neutrophil function and kinetics. Dexamethasone treatment reduced chemotaxis and increased superoxide generation after 1 day and was associated with increased expression of activated beta(2) integrins and reduced L-selectin expression on resting neutrophils. This suggests the appearance of mainly 'activated' cells as a result of demargination and indicates that the effects of indomethacin are distinctive and not related to changes in compartmentalisation.

Current concepts of the actions of paracetamol (acetaminophen) and NSAIDs

There is much uncertainty about the mechanism of action of paracetamol (acetaminophen). It is commonly stated that, unlike the non-steroidal anti-inflammatory drugs (NSAIDs), it is a weak inhibitor of the synthesis of prostaglandins. This conclusion is made largely from studies in which the synthesis of prostaglandins was measured in homogenized tissues. However, in several cellular systems, paracetamol is an inhibitor of the synthesis of prostaglandins with IC(50) values ranging from approximately 4 microM to 200 microM. Paracetamol is not bound significantly to plasma proteins and therefore the concentrations in plasma can be equated directly with those used in in vitro experiments. After oral doses of 1 g, the peak plasma concentrations of paracetamol are approximately 100 microM and the plasma concentrations are therefore in the range where marked inhibition of the synthesis of prostaglandins should occur in some cells. Paracetamol is metabolized by the peroxidase component of prostaglandin H synthase but the relationship of this to inhibition of the cyclooxygenase or peroxidase activities of the enzyme is unclear. Paracetamol is also metabolized by several other peroxidases, including myeloperoxidase, the enzyme in neutrophils which is responsible for the production of hypochlorous acid (HOCl). The metabolism of paracetamol by myeloperoxidase leads to the decreased total production of HOC1 by both intact neutrophils and isolated myeloperoxidase, even though the initial rate of production of HOC1 is increased. The IC(50) value, derived from inhibition of the total production of HOC1 by isolated myeloperoxidase, is 81 microM. Several NSAIDs inhibit functions of neutrophils in media containing low concentrations of protein but their effects, in contrast to that of paracetamol, are generally produced only at concentrations greater than those of the unbound drug in plasma during treatment with the NSAIDs. However, neutrophils isolated during treatment with NSAIDs, such as piroxicam, ibuprofen and indomethacin show decreased function. Paracetamol has little or no anti-inflammatory activity by itself but may potentiate the clinical activity of NSAIDs in the treatment of rheumatoid arthritis.

Inhibition of superoxide anion release from human polymorphonuclear leukocytes by N-acetyl-galactosamine and N-acetyl-glucosamine

This study shows that N-acetyl-galactosamine and N-acetyl-glucosamine can diminish the production of superoxide anion from cytochalasin-B treated PMNs stimulated with FMLP. Inhibition ranged from 80.9% to 1.8%. N-acetyl-galactosamine was superior to N-acetyl-glucosamine, but both showed their action in a dose-related fashion. The mannosamine may diminish the superoxide production, but without a statistical significance. Other sugars such as L-fucose, D-fucose and D-glucose failed to induce inhibition of superoxide generation. Previous reports showed that sugars interfere with carbohydrates lectins interaction. This study shows that aminosugars can do more than interfere with carbohydrates-lectin interaction. The mechanism is not completely known yet. The question whether aminosugars affect cell-cell interaction, regulation of respiratory burst, inflammatory mediators functions, or the glucose uptake and utilization needs further study.

Oxygen radicals, inflammation, and arthritis: pathophysiological considerations and implications for treatment

A vast amount of circumstantial evidence implicates oxygen-derived free radicals, especially superoxide and hydroxyl radical (and to lesser extent, hydrogen peroxide), as mediators of inflammation and/or tissue destruction in inflammatory and arthritic disorders. The substrates for radical generation, namely properly stimulated phagocytic cells, transition metal catalysts, and (to a limited extent) ischemia, are all amply present, although there is no particular rheumatic disease in which a consistent abnormality of radical generation has been identified. These radical species can clearly degrade hyaluronic acid, modify collagen and perhaps proteoglycan structure and/or synthesis, alter and interact with immunoglobulins, activate enzymes and inactivate their inhibitors, and possibly participate in chemotaxis. In most situations, however, there is ample scavenging ability to detoxify these radicals before they hit their target, and many rheumatic disease drugs can decrease their production and/or effects. Despite the apparent sufficiency of natural scavengers and the lack of direct evidence that oxygen radicals are pathogenetically important, substantial pharmaceutical effort is still being made to develop free radical scavengers as therapeutic agents. Although individual free radicals die out quickly, rheumatologic interest in them has been sustained for nearly two decades.