Comparison of the effects of antioxidant non-steroidal anti-inflammatory drugs against myeloperoxidase and hypochlorous acid luminol-enhanced chemiluminescence

Perioperative aspirin improves neurological outcome after focal brain ischemia possibly via inhibition of Notch 1 in rat

BACKGROUND

Perioperative discontinuation of aspirin is often considered due to bleeding concern. We determined whether this discontinuation affected neurological outcome after brain ischemia.

METHODS

Adult male Sprague-Dawley rats were subjected to a 90-minute right middle cerebral arterial occlusion (MCAO). They received 30 mg/kg/day aspirin via gastric gavage: 1) for 2 days at 5 days before MCAO; 2) for 2 days at 5 days before MCAO and for 3 days after MCAO; 3) for 7 days before MCAO; or 4) for 7 days before MCAO and for 3 days after MCAO. Neurological outcome was evaluated 3 days after the MCAO. Ischemic penumbral cortex was harvested 1 or 3 days after MCAO for determining Notch intracellular domain (NICD), IL-6 and IL-1β levels.

RESULTS

Aspirin given by regimen 2 and 3 but not by regimen 1 improved neurological outcome. Neuroprotection was achieved by N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), a Notch activation inhibitor. DAPT and aspirin given only by regimen 2 and 3 reduced NICD, IL-6 and IL-1β in the ischemic penumbral cortex. NICD was found in microglial nuclei. Microglial activation in the ischemic tissues was inhibited by aspirin.

CONCLUSION

Aspirin use during the perioperative period provides neuroprotection. Inhibition of Notch activation and neuroinflammation may contribute to the neuroprotection of aspirin.

Mechanism of action of 5-arninosalicylic acid

5-Aminosalicylic Acid (5-ASA) has been used for over 50 years in the treatment of inflammatory bowel disease in the pro-drug form sulphasalazine (SASP). SASP is also used to treat rheumatoid arthritis. However whether the therapeutic properties of SASP are due to the intact molecule, the 5-ASA or sulphapyridine components is unknown. Several mechanisms of action have been proposed for 5-ASA and SASP including interference in the metabolism of arachidonic acid to prostaglandins and leukotrienes, scavenging,of reactive oxygen species, effects on leucocyte function and production of cytokines. However, it is unlikely that the anti-inflammatory properties of SASP and 5-ASA are due to several different properties but more likely that a single property of 5-ASA explains the theraapeutic effects of 5-ASA and SASP. Reactive oxygen species (ROS) are involved in the metabolism of prostaglandins and leukotrienes and can act as second messengers, and so the scavenging of ROS may be the single mechanism of action of 5-ASA that gives rise to its antiinflammatory effects in both inflammatory bowel disease and rheumatoid arthritis.

The Reactions of Oxicam and Sulfoanilide Non Steroidal Anti-Inflammatory Drugs with Hypochlorous Acid: Determination of the Rate Constants with an Assay Based on the Competition with Para-aminobenzoic Acid Chlorination and Identification of Some Oxidation Products

Hypochlorous acid (HOCl) is an oxygen-derived species involved in physiological processes related to the defence of the organism that may cause adverse effects when its production is insufficiently controlled. In order to examine its reactivity with potential scavenging molecules from the non steroidal anti-inflammatory drugs (NSAIDs) family, a competition assay based on para-aminobenzoic acid (PABA) chlorination was developed. The original optimised in vitro fluorimetric procedure offered the possibility to determine rate constants (ks) for the reaction with HOCl in physiologically relevant conditions. The specificity of the system was improved by a liquid chromatography (LC) which allows the separation of the drugs and their oxidation products. After determination of the rate constant for PABA chlorination by HOCl (mean +/- SD in M(-1) s(-1): 4.3 +/- 0.3 x 10(3)), the applied mathematical model for a chemical competition permits to obtain linear curves from competition studies between several NSAIDs and PABA. Their slopes provided the following rate constants for the different studied drugs: tenoxicam: 4.0 +/- 0.7 x 10(3), piroxicam: 3.6 +/- 0.7 x 10(3), lornoxicam: 4.3 +/- 0.7 x 10(3), meloxicam: 1.7 +/- 0.3 x 10(4), nimesulide: 2.3 +/- 0.6 x 10(2). Meloxicam therefore reacted significantly faster than the other oxicams and nimesulide, which is the weakest scavenger of the studied series. The identification of some of the oxidation products by NMR or MS permitted to explore the reaction mechanism and to examine some aspects of the structure/activity relationships for the molecules of the same chemical family.

Exploitation of the unusual thermodynamic properties of human myeloperoxidase in inhibitor design

Myeloperoxidase plays a fundamental role in oxidant production by neutrophils. It uses hydrogen peroxide and chloride to catalyze the production of hypochlorous acid (HOCl), which contributes to both bacterial killing and oxidative injury of host tissue. Thus, MPO is an interesting target for anti-inflammatory therapy. Here, based on the extraordinary and MPO-specific redox properties of its intermediates compound I and compound II, we present a rational approach in selection and design of reversible inhibitors of HOCl production mediated by MPO. In detail, indole and tryptamine derivatives were investigated for their ability to reduce compounds I and II and to affect the chlorinating activity of MPO. It is shown that these aromatic one-electron donors bound to the hydrophobic pocket at the distal heme cavity and were oxidized efficiently by compound I (k3), which has a one-electron reduction potential of 1.35 V. By contrast, compound II (E degrees ' of the compound II/ferric couple is 0.97 V) reduction (k4) was extremely slow. As a consequence compound II, which does not participate in the halogenation cycle, accumulated. The extent of chlorinating activity inhibition (IC50) was related to the k3/k4 ratio. The most efficient inhibitors were 5-fluorotryptamine and 5-chlorotryptamine with IC50 of 0.79 microM and 0.73 microM and k3/k4 ratios of 386,000 and 224,000, respectively. The reversible mechanism of inhibition is discussed with respect to the enzymology of MPO and the development of drugs against HOCl-dependent tissue damage.

Role of nitric oxide after brain ischaemia

Ischaemic stroke is the second or third leading cause of death in developed countries. In the last two decades substantial research and efforts have been made to understand the biochemical mechanisms involved in brain damage and to develop new treatments. The evidence suggests that nitric oxide (NO) can exert both protective and deleterious effects depending on factors such as the NOS isoform and the cell type by which NO is produced or the temporal stage after the onset of the ischaemic brain injury. Immediately after brain ischaemia, NO release from eNOS is protective mainly by promoting vasodilation; however, after ischaemia develops, NO produced by overactivation of nNOS and, later, NO release by de novo expression of iNOS contribute to the brain damage. This review article summarizes experimental and clinical data supporting the dual role of NO in brain ischaemia and the mechanisms by which NO is regulated after brain ischaemia. We also review NO-based therapeutic strategies for stroke treatment, not only those directly linked with the NO pathway such as NO donors and NOS inhibitors but also those partially related like statins, aspirin or lubeluzole.

High-dose aspirin is neuroprotective in a rat focal ischemia model

Acetylsalicylic acid (ASA) is neuroprotective through various pharmacological action sites. We used a temporary middle cerebral artery occlusion (tMCAO) model in 56 Wistar rats to assess whether repeated ASA injections at 30 min, 6 h, 1, 2, 3, and 4 days after stroke onset are neuroprotective. Animals were sacrificed 5 days after MCAO; infarct size was analyzed with 2,3,5-triphenyltetrazolium chloride staining. As compared to saline (164+/-13 mm(3), n=14), only repeated injections of 40 mg/kg ASA (79+/-18 mm(3), n=14, P=0.0029), but not of 20 mg/kg ASA (129+/-19 mm(3), n=15), reduced infarct volume significantly. No significant change was noted with 40 mg/kg ASA injected only once at 30 min after MCAO (117+/-16 mm(3), n=13).

Inhibition of glutamate release by delaying ATP fall accounts for neuroprotective effects of antioxidants in experimental stroke

Excitotoxic neuronal injury related to excessive glutamate release is believed to play a key role in the pathogenesis of focal cerebral ischemia. Reversal of neuronal glutamate transporters caused by ATP fall and subsequent imbalance of membrane ionic gradients accounts for most glutamate release after cerebral ischemia. ATP synthesis from oxidative phosphorylation derives from the coupled functioning of the mitochondrial respiratory chain (MRC) and the ATP synthase; interestingly, the MRC is one of the main sites of cellular reactive oxygen species (ROS) generation even in physiological circumstances. Hence, we have studied the effect of the antioxidants glutathione, superoxide dismutase, and alpha-tocopherol on infarct outcome, brain ATP, and glutamate levels after permanent middle cerebral artery occlusion (MCAO) in Fischer rats; we have also characterized the actions of antioxidants on MRC complexes. Our results show that intraperitoneal administration of antioxidants 2 h before MCAO enhances ATP synthesis and causes a neuroprotective effect concomitant to inhibition of ischemia-induced increase in brain glutamate. Antioxidants also increased mitochondrial ATP and MRC complex I-III activity and respiration, suggesting that these actions are due to removal of the inhibition caused by endogenous ROS on MRC. These findings may possess important therapeutic repercussions in the management of ischemic stroke.

Aspirin inhibits stress-induced increase in plasma glutamate, brain oxidative damage and ATP fall in rats

The precise mechanisms by which stress induces brain damage are still being elucidated. The high-output, inducible isoform of nitric oxide (NO) synthase (iNOS) is expressed in rat brain after immobilisation stress and its inhibition protects against cell damage in this condition. We have hereby explored some mechanisms involved in iNOS expression and studied the effects of aspirin, a NSAID with neuroprotective actions, in this model. Acute (6 h) stress exposure in rats caused brain expression of iNOS, an increase in plasma glutamate and brain TNF-alpha, induction of oxidative indicators in brain and a fall in brain ATP levels. Prior administration of aspirin (10 mg/kg i.p.) inhibited all these effects caused by stress, suggesting possible therapeutic implications of this drug in this condition.

Neuroprotective effect of aspirin by inhibition of glutamate release after permanent focal cerebral ischaemia in rats

Aspirin reduces the size of infarcts after ischaemic stroke. Although this fact has been attributed to its anti-platelet actions, direct neuroprotective effects have also been reported. We have recently demonstrated that aspirin is neuroprotective by inhibiting glutamate release in 'in vitro' models of brain ischaemia, via an increase in ATP production. The present study was designed to determine whether the inhibition of glutamate release induced by aspirin might be protective in a whole-animal model of permanent focal brain ischaemia. Focal brain ischaemia was produced in male adult Fischer rats by occluding both the common carotid and middle cerebral arteries. Central and serum glutamate levels were determined at fixed intervals after occlusion. The animals were then killed and infarct volume was measured. Aspirin (30 mg/kg i.p. administered 2 h before the occlusion) produced a significant reduction in infarct volume, an effect that correlated with the inhibition caused by aspirin on ischaemia-induced increase in brain and serum glutamate concentrations after the onset of the ischaemia. Aspirin also inhibited ischaemia-induced decrease in brain ATP levels. Our present findings show a novel mechanism for the neuroprotective effects of aspirin, which takes place at concentrations in the anti-aggregant-analgesic range, useful in the management of patients with risk of ischaemic events.

Mechanisms of the neuroprotective effect of aspirin after oxygen and glucose deprivation in rat forebrain slices

Acetylsalicylic acid (ASA, Aspirin) is an anti-inflammatory drug with a wide spectrum of pharmacological activities and multiple sites of action. Apart from its preventive actions against stroke due to its antithrombotic properties, recent data in the literature suggest that high concentrations of ASA also exert direct neuroprotective effects. We have used an in vitro model of brain ischaemia using rat forebrain slices deprived of oxygen and glucose to test ASA neuroprotective properties. We have found that ASA inhibits neuronal damage at concentrations lower than those previously reported (0.1-0.5 mM), and that these effects correlate with the inhibition of excitatory amino acid release, of NF-kappaB translocation to the nucleus and iNOS expression caused by ASA. All of these three mechanisms may mediate the neuroprotective effects of this drug. Our results also show that the effects of ASA are independent of COX inhibition. Taken together, our present findings show that ASA is neuroprotective in an in vitro model of brain ischaemia at doses close to those recommended for its antithrombotic effects.

The in vitro effects of new non-steroidal antiinflammatory compounds on antioxidant system of human erythrocytes

It has been reported by our group that some benzoxazolone and benzothiazolone derivatives showed significant antinociceptive and anti-inflammatory activity [DOGRUER et al. 1997]. It has been speculated that nonsteroidal anti-inflammatory drugs (NSAIDs) can act as the free radical scavengers and possess antioxidant activity. It is also well documented that oxidative stress can play an important role in the side effects of many xenobiotics including NSAIDs. Therefore, in the present study, the effects of six of the above mentioned benzoxazolone and benzothiazolone derivatives bearing 2-pyridylaminocarbonylmetyl moiety at the position 3 (I) on the antioxidant system-related parameters of human erythrocytes have been investigated. Diclofenac and nimesulid were also tested in the same systems as the control, because they are commonly used as NSAIDs. Our results showed that these compounds made significant changes in the antioxidant system of human erythrocyte.

The oxidative inactivation of tissue inhibitor of metalloproteinase-1 (TIMP-1) by hypochlorous acid (HOCI) is suppressed by anti-rheumatic drugs

Tissue inhibitors of metalloproteinases (TIMPs) prevent uncontrolled connective tissue destruction by limiting the activity of matrix metalloproteinases (MMPs). That TIMPs should be susceptible to oxidative inactivation is suggested by their complex tertiary structure which is dependent upon 6 disulphide bonds. We examined the oxidative inactivation of human recombinant TIMP-1 (hr TIMP-1) by HOCl and the inhibition of this process by anti-rheumatic agents. TIMP-1 was exposed to HOCl in the presence of a variety of disease modifying anti-rheumatic drugs. TIMP-1 activity was measured by its ability to inhibit BC1 collagenase activity as measured by a fluorimetric assay using the synthetic peptide substrate (DNP-Pro-Leu-Ala-Leu-Trp-Ala-Arg), best cleaved by MMP-1. The neutrophil derived oxidant HOCl, but not the derived oxidant N-chlorotaurine, can inactivate TIMP-1 at concentrations achieved at sites of inflammation. Anti-rheumatic drugs have the ability to protect hrTIMP-1 from inactivation by HOCl. For D-penicillamine, this effect occurs at plasma levels achieved with patients taking the drug but for other anti-rheumatic drugs tested this occurs at relatively high concentrations that are unlikely to be achieved in vivo, except possibly in a microenvironment. These results are in keeping with the concept that biologically derived oxidants can potentiate tissue damage by inactivating key but susceptible protein inhibitors such as TIMP-1 which form the major local defence against MMP induced tissue breakdown.

Characterization of drugs as antioxidant prophylactics

There is growing interest in the evaluation of drugs (prescription only medicines and over-the-counter medicines) as antioxidant prophylactics. Although free radical mechanism in human degenerative diseases is now generally recognised, the mechanisms of tissue injury in humans are very complex and it may not be possible to clearly identify the role played by free radicals in the process. This review examines the current evidence to support the notion that drugs for a particular therapeutic category might possess useful antioxidant capacity hence minimising tissue injury due to free radicals.

Effects of nonsteroidal antiinflammatory drugs on oxidative pathways in A/J mice

The tobacco-specific N-nitrosamine, NNK, is a potent carcinogen in laboratory animals. The authors have shown previously that NNK-induced lung tumorigenesis in A/J mice can be reduced significantly by certain nonsteroidal antiinflammatory drugs (NSAIDs), such as sulindac, ibuprofen, or piroxicam treatments. In this study, the authors investigated whether NSAIDs could reduce NNK-induced oxidative, DNA damage and/or inhibit endogenous lipid peroxidation, or prostaglandin E2 (PGE2) synthesis in A/J mice. In the first experiment, A/J mice were gavaged with NNK (112 mumol/kg b.w.) three times a week while being maintained on a diet to which either ibuprofen (263 mg/kg diet), naproxen (230 mg/kg), sulindac (123 mg/kg), piroxicam (25 mg/kg), indomethacin (5 mg/kg), or no NSAIDs had been added. Levels of 8-OH-dG in the DNA of lung and liver were measured by high-performance liquid chromatography with electron capture detector. Treatment with NSAIDs had no significant effects on the endogenous or NNK-induced formation of 8-OH-dG in the lung of the mice. In a second experiment, after treatment of A/J mice with NSAIDs for 2 weeks, lipid peroxidation was assayed by determining thiobarbituric acid-reactive substances (TBA-RS) in lung tissues, and prostaglandin E2 levels were measured in plasma by an enzyme immunoassay. Treatments with some NSAIDs lowered the levels of lipid peroxidation and plasma levels of PGE2 below basal levels. Taken together, these results suggest that the inhibition of NNK-induced lung tumorigenesis by NSAIDs is more likely related to an inhibition of prostaglandin synthesis than to a direct inhibition of lipid peroxidation or oxidative DNA damage induced by NNK.

Retinoids inhibit the respiratory burst and degranulation of stimulated human polymorphonuclear leukocytes

Retinoids exhibit a wide spectrum of activities, including antiinflammatory properties. We have investigated the effect of retinoic acid (RA) and retinyl acetate (RAc) on the production of reactive oxygen metabolites and the release of lysosomal enzymes by human polymorphonuclear leukocytes (PMN). Incubation of PMN with RAc or RA (1-100 microM) caused a dose-dependent inhibition (upto 90%) in O2- production and chemiluminescence induced by phorbol myristate acetate (PMA), N-formyl-methionyl-leucyl-phenylanaline (fMLP), opsonized zymosan or ionophore A23187. Both retinoids (1-100 microM) also inhibited, in a dose-dependent way, degranulation induced by fMLP (upto 85% at the highest concentration of RA). These inhibitory effects appear irreversible, since they persist after the drugs are removed and the cells washed before stimulation. Inhibitors of cyclo-oxygenase activity such as acetylsalicyclic acid and indomethacin did not influence the effects of RAc. In contrast, BW755, an inhibitor of both cyclooxygenase and lipoxygenase, reversed the inhibitory action of RAc, suggesting that the effect of retinoids occurs possibly through the mediation of lipoxygenase products. The modulation of PMN oxidative metabolism and degranulation might help explain the antiinflammatory properties of retinoids.

Mechanism of inhibition of myeloperoxidase by anti-inflammatory drugs

Hypochlorous acid (HOCl) is the most powerful oxidant produced by human neutrophils, and should therefore be expected to contribute to the damage caused by these inflammatory cells. It is produced from H2O2 and Cl- by the heme enzyme myeloperoxidase (MPO). We used a H2O2-electrode to assess the ability of a variety of anti-inflammatory drugs to inhibit conversion of H2O2 to HOCl. Dapsone, mefenamic acid, sulfapyridine, quinacrine, primaquine and aminopyrine were potent inhibitors, giving 50% inhibition of the initial rate of H2O2 loss at concentrations of about 1 microM or less. Phenylbutazone, piroxicam, salicylate, olsalazine and sulfasalazine were also effective inhibitors. Spectral investigations showed that the inhibitors acted by promoting the formation of compound II, which is an inactive redox intermediate of MPO. Ascorbate reversed inhibition by reducing compound II back to the active enzyme. The characteristic properties that allowed the drugs to inhibit MPO reversibly were ascertained by determining the inhibitory capacity of related phenols and anilines. Inhibition increased as substituents on the aromatic ring became more electron withdrawing, until an optimum reduction potential was reached. Beyond this optimum, their inhibitory capacity declined. The best inhibitor was 4-bromoaniline which had an I50 of 45 nM. An optimum reduction potential enables inhibitors to reduce MPO to compound II, but prevents them from reducing compound II back to the active enzyme. Exploitation of this optimum reduction potential will help in targeting drugs against HOCl-dependent tissue damage.

Inhibition of the myeloperoxidase-H2O2-Cl- system of neutrophils by indomethacin and other non-steroidal anti-inflammatory drugs

The results presented herein demonstrate that the non-steroidal anti-inflammatory drug (NSAID) indomethacin is a strong inhibitor of the formation of HOCl by murine neutrophils (50% inhibition at 15 microM). Addition of 40 microM indomethacin to activated neutrophils caused 80% inhibition of HOCl formation throughout a 60-min time course while slightly increasing the levels of O2- and H2O2 produced. Comparable degrees of inhibition were achieved when the cells were stimulated with phorbol myristate acetate and with opsonized zymosan. Control experiments indicated that the drug did not act by scavenging HOCl. Direct inhibition of the chlorinating activity of myeloperoxidase (MPO) was confirmed using highly purified human enzyme in vitro. Kinetic analysis of the mechanism of inhibition showed that the drug was competitive with respect to Cl- and uncompetitive with respect to H2O2, showing a Ki of 37 microM. In contrast to its inhibition of the oxidation of Cl- by MPO, indomethacin had no effect on the peroxidative activity of the enzyme (oxidation of 4-aminoantipyrene), nor did it inhibit the activity of several other enzymes involved in H2O2 metabolism, including horseradish peroxidase, catalase, xanthine oxidase, and superoxide dismutase. Finally, it was found that inhibition of HOCl formation was a shared but non-uniform property of many NSAIDs; piroxicam, salicylate, sulindac, ibuprofen, and aspirin were all inhibitory but at widely different concentrations [Ki(app) values of 0.05, 0.18, 0.18, greater than 1, and 3 mM respectively] that correlated only partially with their therapeutic dose range. The results encourage further studies into the possibility that inhibition of HOCl formation may constitute an additional mechanism whereby NSAIDs reduce tissue destruction in chronically inflamed tissues.

Naphthalenes as inhibitors of myeloperoxidase: direct and indirect mechanisms of inhibition

Control of myeloperoxidase (MPO) may be an important consideration in disorders where excessive PMN elastase activity is a significant factor. There are, however, two mechanisms for the apparent regulation of MPO: 1) inhibit the enzyme directly, and ii) prevent the ensuing HOC1 induced oxidation by using a surrogate reducing agent. Appropriate methodology has been devised to distinguish true MPO inhibitors. With the exception of NaN3, many MPO inhibitors fall into the latter category and do not actually regulate the enzyme. Several potent organic inhibitors have been discovered, which, because of their structural selectivity, appear to associate specifically with a binding site on the enzyme, rather than attaching indiscriminately to a hydrophobic domain. By controlling the enzyme, these compounds protect alpha-1-PI from MPO induced damage, and could serve better than antioxidants to define the role of MPO in elastase induced injury.

Biologically-significant scavenging of the myeloperoxidase-derived oxidant hypochlorous acid by some anti-inflammatory drugs

Neutrophils contain the enzyme myeloperoxidase, which oxidizes Cl- ions into the powerful oxidant hypochlorous acid (HOCl). HOCl inactivates alpha 1-antiprotease, permitting uncontrolled protease activities. Most anti-inflammatory drugs tested are capable of reacting with HOCl, but the reactions seem insufficiently rapid under physiological conditions to protect alpha 1-antiprotease against inactivation by HOCl. However, rapid scavenging of HOCl might contribute to the anti-inflammatory effects of penicillamine, gold sodium thiomalate, phenylbutazone and primaquine.

The scavenging of oxidants by sulphasalazine and its metabolites. A possible contribution to their anti-inflammatory effects?

Sulphasalazine (Salazopyrin) and its metabolites sulphapyridine and 5-aminosalicylate are powerful scavengers of the hydroxyl radical, determined by pulse radiolysis and confirmed by assays based on deoxyribose degradation by hydroxyl radicals. 5-Aminosalicylate can also protect alpha 1-antiprotease against attack by the myeloperoxidase-derived oxidant hypochlorous acid. The ability to scavenge oxidants produced at sites of inflammation may contribute to the anti-inflammatory action of sulphasalazine and its metabolites.

Antiarthritic drugs containing thiol groups scavenge hypochlorite and inhibit its formation by myeloperoxidase from human leukocytes. A therapeutic mechanism of these drugs in rheumatoid arthritis?

We investigated the effect of antiarthritic drugs containing thiol groups, such as D-penicillamine, tiopronin (N-[2-mercaptopropionyl]glycine), sodium aurothiomalate, and aurothioglucose, on the chlorinating activity of myeloperoxidase purified from human leukocytes. Hypochlorite, the reactive product of the reaction catalyzed by myeloperoxidase, was effectively scavenged by these antiarthritic drugs, and in addition, D-penicillamine and tiopronin inhibited myeloperoxidase itself. The above-mentioned effects of these drugs were observed at concentrations that occur in the serum of rheumatoid arthritis patients treated with these agents. We suggest that the therapeutic effect of these antiarthritic drugs may be due to the protection of tissues against the reactive HOCI released by activated granulocytes at inflamed sites.

The reactivity of neutrophils at the site of an acute inflammatory reaction as measured by chemiluminescence

In this study the technique of luminol-enhanced chemiluminescence (LECL), which was shown to be dependent on the generation of superoxide anion, has been employed to investigate the reactivity of polymorphonuclear leukocytes found at the site of inflammation. Cells derived from the pleural cavity of rats undergoing an acute inflammatory reaction initiated by an intrapleural injection of calcium pyrophosphate or normal serum demonstrated a significantly higher chemiluminescent response compared to cells derived from animals injected with plasma, saline or phosphate-buffered saline. In addition in vitro studies showed that calcium pyrophosphate crystals could stimulate the cells per se and could increase their reactivity.

The effect of D-penicillamine on human myeloperoxidase, a mechanism for the efficacy of the drug in rheumatoid arthritis

We investigated the effect of D-penicillamine on the ability of myeloperoxidase, purified from human leukocytes, to catalyse the oxidation of chloride ions to hypochlorite (HOCl) in the presence of H2O2. It is shown that, due to the interaction of D-penicillamine with both myeloperoxidase itself and HOCl, the chlorinating activity of myeloperoxidase in the presence of H2O2 and chloride ions is prevented. A concentration of 100 microM D-penicillamine inhibits the chlorinating activity of myeloperoxidase completely, which Is due to the stabilization of Compound II, an inactive form of the enzyme. In addition, HOCl reacts directly with D-penicillamine. Analysis of the reaction products of D-penicillamine and HOCl showed that D-penicillamine was oxidized to penicillamine disulphide and penicillamine sulphinic acid, and eventually deaminated (indicated by the release of ammonia). Lower concentrations of D-penicillamine (10 microM) inhibited myeloperoxidase less, but still acted as effective scavengers of HOCl. In very low concentrations (1 microM), D-penicillamine did not scavenge HOCl effectively, but rather stimulated the chlorinating activity of myeloperoxidase. However, when instead of D-penicillamine a comparable amount of ascorbate was added, a similar but even larger stimulation was observed. Since the concentration of free D-penicillamine in serum from rheumatoid patients treated with this drug is about 20 microM (Saetre, R. and Rabenstein, D.L. (1978) Anal. Chem. 50, 276-280), the therapeutic effect of D-penicillamine may be due to the protection of tissues against the reactive HOCl released by activated granulocytes at inflammation sites.

Benoxaprofen stimulates proteoglycan synthesis in normal canine knee cartilage in vitro

Several nonsteroidal antiinflammatory drugs which are cyclooxygenase inhibitors (e.g., salicylates, fenoprofen, ibuprofen) have been shown to suppress proteoglycan synthesis by normal joint cartilage in vitro. We examined the effect of benoxaprofen, a long-acting proprionic acid derivative which inhibits lipoxygenase in addition to causing moderate cyclooxygenase inhibition. When added to the culture medium in concentrations comparable with those obtainable in serum of patients treated with the drug (e.g., 10 and 50 micrograms/ml), benoxaprofen increased proteoglycan synthesis in slices of normal canine knee cartilage to 126% and 135%, respectively, of control levels. These concentrations of the drug augmented net protein synthesis to 154% and 123%, respectively, of control levels. Incorporation of 3H glucosamine into 9-aminoacridine precipitable material was increased by benoxaprofen, showing that it stimulates net proteoglycan synthesis, and not merely sulfation. At concentrations of either 10 or 50 micrograms/ml, the drug had no effect on proteoglycan catabolism or on the ability of proteoglycans to interact with cartilage hyaluronic acid to form macromolecular aggregates. Nordihydroguaiaretic acid, a free radical scavenger which, like benoxaprofen, inhibits the lipoxygenase as well as cyclooxygenase pathways of arachidonic acid metabolism, also increased 35S glycosaminoglycan synthesis in cartilage slices. The stimulation of glycosaminoglycan and protein synthesis by benoxaprofen suggests that its action on the chondrocyte may be different from that of most other nonsteroidal antiinflammatory drugs.