Synergistic effects of thalidomide and poly (ADP-ribose) polymerase inhibition on type II collagen-induced arthritis in mice

Preclinical Characterization of Pharmacologic NAD+ Boosting as a Promising Therapeutic Approach in Rheumatoid Arthritis

OBJECTIVE

We analyzed NAD+ metabolism in patients with rheumatoid arthritis (RA), its association with disease activity and clinical outcomes of RA, and the therapeutic potential of pharmacologic NAD+ boosting.

METHODS

Our study included 253 participants. In the first cohort, comprising 153 RA patients and 56 healthy donors, we assessed NAD+ levels and NAD+ -related gene pathways. We analyzed 92 inflammatory molecules by proximity extension assay. In the second cohort, comprising 44 RA patients starting anti-tumor necrosis factor (anti-TNF) drugs, we evaluated changes in NAD+ levels and their association with clinical response after 3 months. Mechanistic studies were performed ex vivo on peripheral blood mononuclear cells (PBMCs) from patients with RA to test the beneficial effects of NAD+ boosters, such as nicotinamide and nicotinamide riboside.

RESULTS

Reduced NAD+ levels were found in RA samples, in line with altered activity and expression of genes involved in NAD+ consumption (sirtuins, poly[ADP-ribose] polymerase, CD38), transport (connexin 43), and biosynthesis (NAMPT, NMNATs). Unsupervised clustering analysis identified a group of RA patients with the highest inflammatory profile, the lowest NAD+ levels, and the highest disease activity (as shown by the Disease Activity Score in 28 joints). NAD+ levels were modulated by anti-TNF therapy in parallel with the clinical response. In vitro studies using PBMCs from RA patients showed that nicotinamide riboside and nicotinamide increased NAD+ levels via NAMPT and NMNAT and reduced their prooxidative, proapoptotic, and proinflammatory status.

CONCLUSION

RA patients display altered NAD+ metabolism, directly linked to their inflammatory and disease activity status, which was reverted by anti-TNF therapy. The preclinical beneficial effects of NAD+ boosters, as shown in leukocytes from RA patients, along with their proven clinical safety, might pave the way for the development of clinical trials using these compounds.

Diverse therapeutic efficacies and more diverse mechanisms of nicotinamide

BACKGROUND

Nicotinamide (NAM) is a form of vitamin B3 that, when administered at near-gram doses, has been shown or suggested to be therapeutically effective against many diseases and conditions. The target conditions are incredibly diverse ranging from skin disorders such as bullous pemphigoid to schizophrenia and depression and even AIDS. Similar diversity is expected for the underlying mechanisms. In a large portion of the conditions, NAM conversion to nicotinamide adenine dinucleotide (NAD⁺) may be a major factor in its efficacy. The augmentation of cellular NAD⁺ level not only modulates mitochondrial production of ATP and superoxide, but also activates many enzymes. Activated sirtuin proteins, a family of NAD⁺-dependent deacetylases, play important roles in many of NAM's effects such as an increase in mitochondrial quality and cell viability countering neuronal damages and metabolic diseases. Meanwhile, certain observed effects are mediated by NAM itself. However, our understanding on the mechanisms of NAM's effects is limited to those involving certain key proteins and may even be inaccurate in some proposed cases.

AIM OF REVIEW

This review details the conditions that NAM has been shown to or is expected to effectively treat in humans and animals and evaluates the proposed underlying molecular mechanisms, with the intention of promoting wider, safe therapeutic application of NAM.

KEY SCIENTIFIC CONCEPTS OF REVIEW

NAM, by itself or through altering metabolic balance of NAD⁺ and tryptophan, modulates mitochondrial function and activities of many molecules and thereby positively affects cell viability and metabolic functions. And, NAM administration appears to be quite safe with limited possibility of side effects which are related to NAM's metabolites.

Poly(ADP-Ribose) Polymerases in Host-Pathogen Interactions, Inflammation, and Immunity

The literature review presented here details recent research involving members of the poly(ADP-ribose) polymerase (PARP) family of proteins. Among the 17 recognized members of the family, the human enzyme PARP1 is the most extensively studied, resulting in a number of known biological and metabolic roles. This review is focused on the roles played by PARP enzymes in host-pathogen interactions and in diseases with an associated inflammatory response. In mammalian cells, several PARPs have specific roles in the antiviral response; this is perhaps best illustrated by PARP13, also termed the zinc finger antiviral protein (ZAP). Plant stress responses and immunity are also regulated by poly(ADP-ribosyl)ation. PARPs promote inflammatory responses by stimulating proinflammatory signal transduction pathways that lead to the expression of cytokines and cell adhesion molecules. Hence, PARP inhibitors show promise in the treatment of inflammatory disorders and conditions with an inflammatory component, such as diabetes, arthritis, and stroke. These functions are correlated with the biophysical characteristics of PARP family enzymes. This work is important in providing a comprehensive understanding of the molecular basis of pathogenesis and host responses, as well as in the identification of inhibitors. This is important because the identification of inhibitors has been shown to be effective in arresting the progression of disease.

The Role of Poly(ADP-ribose) Polymerase-1 in Rheumatoid Arthritis

Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear enzyme with a crucial role in the maintenance of genomic stability. In addition to the role of PARP-1 in DNA repair, multiple studies have also demonstrated its involvement in several inflammatory diseases, such as septic shock, asthma, atherosclerosis, and stroke, as well as in cancer. In these diseases, the pharmacological inhibition of PARP-1 has shown a beneficial effect, suggesting that PARP-1 regulates their inflammatory processes. In recent years, we have studied the role of PARP-1 in rheumatoid arthritis, as have other researchers, and the results have shown that PARP-1 has an important function in the development of this disease. This review summarizes current knowledge on the effects of PARP-1 in rheumatoid arthritis.

Mechanism of immunomodulatory drugs' action in the treatment of multiple myeloma

Although immunomodulatory drugs (IMiDs), such as thalidomide, lenalidomide, and pomalidomide, are widely used in the treatment of multiple myeloma (MM), the molecular mechanism of IMiDs' action is largely unknown. In this review, we will summarize recent advances in the application of IMiDs in MM cancer treatment as well as their effects on immunomodulatory activities, anti-angiogenic activities, intervention of cell surface adhesion molecules between myeloma cells and bone marrow stromal cells, anti-inflammatory activities, anti-proliferation, pro-apoptotic effects, cell cycle arrest, and inhibition of cell migration and metastasis. In addition, the potential IMiDs' target protein, IMiDs' target protein's functional role, and the potential molecular mechanisms of IMiDs resistance will be discussed. We wish, by presentation of our naive discussion, that this review article will facilitate further investigation in these fields.

The Val762Ala polymorphism in the poly(ADP-ribose) polymerase-1 gene is not associated with susceptibility in Turkish rheumatoid arthritis patients

The findings of the studies on poly(ADP-ribose) polymerase-1 (PARP-1) have suggested that the enzyme inactivation provides significant protection against systemic or tissue inflammation in animal models. It has also shown that the single-nucleotide polymorphism (Val762Ala) of the PARP-1 causes about 40% decrease of enzyme activity. The aim of this study was to analyze the association of the PARP-1 Val762Ala polymorphism in Turkish patients with rheumatoid arthritis. A total of 128 RA patients and 165 normal controls from the same geographic region were studied and polymerase chain reaction (PCR)-based restriction analysis was used to identify Val762Ala polymorphism of the PARP-1. Association analyses were performed using chi (2) tests. Our results indicated that the distribution of the PARP-1 genotypes and alleles did not differ significantly among subjects with or without RA (P > 0.05). The results of the study indicate that, for our Turkish sample, the V762A polymorphism of the PARP-1 may not be involved in susceptibility to RA, implying that the polymorphism may not function as a candidate gene marker for screening RA patients.

Angiogenesis inhibition as a therapeutic approach for inflammatory synovitis

Angiogenesis inhibition, long studied in the treatment of malignancies, has begun to emerge as a potential therapeutic approach in managing inflammatory arthritis, particularly rheumatoid arthritis. The growth of new vessels is required for the development of the rheumatoid pannus, which then leads to extensive synovial inflammation and joint destruction. Vascular endothelial growth factor is the best studied mediator of angiogenesis, and several therapies have been developed that specifically target this molecule. Several other angiogenesis mediators, such as the angiopoietin-TIE system, hypoxia inducible factor and integrin alpha(V)beta(3), as well as naturally occurring inhibitors of angiogenesis, are also being investigated as potential therapeutic targets. Additionally, there are a number of drugs, including paclitaxel, 2-methoxyestradiol and fumagillin analogs, that might have a role in inhibiting angiogenesis and, thus, in treating proliferative synovitis.

Poly (ADP-ribose) polymerase activation and circulatory shock

Sepsis is associated with increased production of reactive oxidant species. Oxidative and nitrosative stress can lead to activation of the nuclear enzyme poly (ADP-ribose) polymerase (PARP), with subsequent loss of cellular functions. Activation of PARP may dramatically lower the intracellular concentration of its substrate, NAD thus slowing the rate of glycolysis, electron transport and subsequently ATP formation. This process can result in cell dysfunction and cell death. In addition, PARP enhances the expression of various pro-inflammatory mediators, via activation of NF-kappaB, MAP kinase and AP-1 and other signal transduction pathways. Preclinical studies in various rodent and large animal models demonstrate that PARP inhibition or PAR deficiency exerts beneficial effects on the haemodynamic and metabolic alterations associated with septic and haemorrhagic shock. Recent human data also support the role of PARP in septic shock: In a retrospective study in 25 septic patients, an increase in plasma troponin level was related to increased mortality risk. In patients who died, significant myocardial damage was detected, and histological analysis of heart showed inflammatory infiltration, increased collagen deposition, and derangement of mitochondrial criptae. Immunohistochemical staining for poly(ADP-ribose) (PAR), the product of activated PARP was demonstrated in septic hearts. There was a positive correlation between PAR staining and troponin I; and a correlation of PAR staining and LVSSW. Thus, there is significant PARP activation in animal models subjected to circulatory shock, as well as in the hearts of septic patients. Based on the interventional studies in animals and the correlations observed in patients we propose that PARP activation may be, in part responsible for the cardiac depression and haemodynamic failure seen in humans with severe sepsis. Interestingly, recent studies reveal that the protective effects of PARP inhibitors are predominant in male animals, and are not apparent in female animals. Oestrogen, by providing a baseline inhibitory effect on PARP activation, may be partially responsible for this gender difference.

Drugs to suppress cough

Cough is an important defensive reflex of the airway and also a common symptom of respiratory disease. Cough after common respiratory virus infection is transient but is more persistent when associated with conditions such as asthma, rhinosinusitis, gastro-oesophageal reflux, chronic obstructive pulmonary disease and lung cancer. Persistent cough may be due to peripheral and/or central sensitisation of cough reflexes initiated by cough receptors, rapidly adapting receptors or nociceptors. Treatment directed at associated conditions such as asthma (with anti-inflammatories) and gastro-oesophageal reflux (with proton-pump inhibitors) improve cough. There remains a need to use drugs that suppress the neural activity of cough (termed nonspecific), as treatments directed at the clinical cause(s) of the underlying cough (termed specific) may not be effective. The most effective indirect antitussives are opioids such as morphine, codeine or pholcodeine, but they produce side effects such as drowsiness, nausea, constipation and physical dependence. Opioids such as kappa- and delta-receptor agonists, non-opioids such as nociceptin, neurokinin and bradykinin receptor antagonists, cannabinoids, vanilloid receptor-1 antagonists, blockers of Na+-dependent channels, and large conductance Ca2+-dependent K+-channel activators of afferent nerves may represent novel antitussives.

Shock, inflammation and PARP

The activation of poly(ADP-ribose) polymerase (PARP) is well considered to play an important role in various patho-physiological conditions like inflammation and shock. A vast amount of circumstantial evidence implicates oxygen-derived free radicals (especially, superoxide and hydroxyl radical) and high-energy oxidants (such as peroxynitrite) as mediators of inflammation and shock. ROS (e.g., superoxide, peroxynitrite, hydroxyl radical and hydrogen peroxide) are all potential reactants capable of initiating DNA single strand breakage, with subsequent activation of the nuclear enzyme poly(ADP-ribose) synthetase (PARS), leading to eventual severe energy depletion of the cells, and necrotic-type cell death. During the last years, numerous experimental studies have clearly demonstrated the beneficial effects of PARP inhibition in cell cultures through rodent models and more recently in pre-clinical large animal models of acute and chronic inflammation. The aim of this review is to describe recent experimental evidence implicating PARP as a pathophysiological modulator of acute and chronic inflammation.

Poly(ADP-ribose) polymerase activation by reactive nitrogen species--relevance for the pathogenesis of inflammation

Oxidative and nitrosative stress triggers DNA strand breakage, which then activates the nuclear enzyme poly(ADP-ribose) polymerase (PARP). Nitrogen-derived reactive oxidant species capable of involving DNA single strand breakage and PARP activation include peroxynitrite (the reaction product of nitric oxide and superoxide), but not nitric oxide per se. Activation of PARP may dramatically lower the intracellular concentration of its substrate, nicotinamide adenine dinucleotide, thus slowing the rate of glycolysis, electron transport, and subsequently ATP formation. This process can result in cell dysfunction and cell death. Here we review the role of reactive nitrogen species in the process of PARP activation, followed by the effect of pharmacological inhibition or genetic inactivation of PARP on the course of various forms of inflammation.

New antiangiogenic strategies for the treatment of proliferative synovitis

Angiogenesis inhibition, which has been extensively studied for the treatment of various malignancies, is beginning to emerge as a new potential therapy for proliferative synovitis, particularly rheumatoid arthritis (RA). The rheumatoid pannus, the site of inflammation and joint destruction in the rheumatoid synovium, relies on the development of new vasculature to sustain its growth. A host of mediators have been shown to induce angiogenesis at the site of the inflamed synovium; these include vascular endothelial growth factor, fibroblast growth factor, integrin alpha(V)beta3, angiopoietin, prosta-glandin E1 and prostaglandin E2, and matrix metalloproteinases. In addition, hypoxia at the site of synovial inflammation contributes to angiogenesis stimulation. Several naturally-occurring inhibitors exist, such angiostatin and endostatin. There are a number of drugs undergoing study in the treatment of proliferative synovitis, which capitalise on the correlation between angiogenesis inhibition and the reduction of signs and symptoms of RA. Paclitaxel and an anti-integrin alpha(V)beta3 antibody, LM-609, are currently in clinical trials. Other drugs that may inhibit angiogenesis in RA include TNP-470 (formerly called AGM-1470), PPI-2458, PTK-787, bevacizumab and thalidomide. Many of these drugs have shown promise for the treatment of oncologic disorders, and are now being evaluated for the treatment of proliferative synovitis.

Nicotinamide: a potential addition to the anti-psoriatic weaponry

Psoriasis is an inflammatory disorder characterized by a T helper type 1 cell cytokine pattern. Increased expression of adhesion molecules, prominent neutrophil accumulation, and increased production of nitric oxide are characteristics of this disorder. Moreover, histamine and proteases are supposed to participate in the pathogenesis of psoriasis. Nicotinamide is an inhibitor of poly (ADP-ribose) polymerase-1 (PARP-1) that, through enhancement of nuclear kappa B-mediated transcription, plays a pivotal role in the expression of inflammatory cytokines, chemokines, adhesion molecules, and inflammatory mediators. Through interaction with CD38 and inhibition of IL-1, IL-12, and TNF-alpha production, nicotinamide produces a mild TH2 bias. Nicotinamide is a potent phosphodiesterase inhibitor and suppresses neutrophil chemotaxis and mast cell histamine release. It inhibits nitric oxide synthase mRNA induction and suppresses antigen-induced lymphocyte transformation. Nicotinamide increases the biosynthesis of ceramides, which upon degradation produce sphingosine. Sphingosine inhibits protein kinase C (PKC) and decreases basal cell proliferation dependent on PKC. Taken together, it can be reasoned that nicotinamide could be a useful addition to anti-psoriatic armamentarium. The combination of nicotinamide and thalidomide or methotrexate provided a powerful synergistic inhibition of murine collagen-induced arthritis. Nicotinamide decreased the methotrexate-induced hepatotoxicity. The above combinations may prove to have a powerful anti-psoriatic effect as well. As PARP inhibitors could exert anti-retroviral effect, nicotinamide could also be of special value in the treatment of HIV-infected psoriatics.

Inhibition of NF-kappa B activity by thalidomide through suppression of IkappaB kinase activity

The sedative and anti-nausea drug thalidomide, which causes birth defects in humans, has been shown to have both anti-inflammatory and anti-oncogenic properties. The anti-inflammatory effect of thalidomide is associated with suppression of cytokine expression and the anti-oncogenic effect with inhibition of angiogenesis. It is presently unclear whether the teratogenic properties of thalidomide are connected in any way to the beneficial, anti-disease characteristics of this drug. The transcription factor NF-kappaB has been shown to be a key regulator of inflammatory genes such as tumor necrosis factor-alpha and interleukin-8. Inhibition of NF-kappaB is associated with reduced inflammation in animal models, such as those for rheumatoid arthritis. We show here that thalidomide can block NF-kappaB activation through a mechanism that involves the inhibition of activity of the IkappaB kinase. Consistent with the observed inhibition of NF-kappaB, thalidomide blocked the cytokine-induced expression of NF-kappaB-regulated genes such as those encoding interleukin-8, TRAF1, and c-IAP2. These data indicate that the therapeutic potential for thalidomide may be based on its ability to block NF-kappaB activation through suppression of IkappaB kinase activity.

Inhibition of poly(ADP-ribose) polymerase attenuates cerebral vasospasm after subarachnoid hemorrhage in rabbits

BACKGROUND AND PURPOSE

Poly(ADP-ribose) polymerase (PARP) is important in modulating inflammation, which has been implicated in cerebral vasospasm after subarachnoid hemorrhage (SAH). We investigated the role of PARP in vasospasm using 3-aminobenzamide (3-AB), a PARP inhibitor, in a rabbit model.

METHODS

Twenty-four New Zealand White rabbits were divided into 4 groups: (1) no treatment (control group, n=6); (2) blood injection without pretreatment (SAH-only group, n=6); (3) blood injection with pretreatment by vehicle (SAH+vehicle group, n=6); and (4) blood injection with pretreatment by 3-AB (SAH+3-AB group, n=6). We used the single-hemorrhage model of SAH, injecting autologous arterial blood into the cisterna magna. Angiography was performed before (baseline) and after (day 2) SAH, and the diameter of the basilar artery (BA) was measured. Animals were euthanatized after the second angiogram. After perfusion and fixation, the brains were cut into sections for hematoxylin and eosin and immunohistochemical staining for poly(ADP-ribosyl)ation.

RESULTS

In the control group, there were no differences in the BA lumen caliber between baseline and day 2 (96.8+/-10.4%). Cerebral vasospasm in the SAH+3-AB group (88.2+/-6. 2%) was remarkably attenuated in comparison with that in the SAH-only group (64.9+/-8.0%) and the SAH+vehicle group (65.6+/-10. 8%). The BA in the SAH+3-AB group showed less corrugation of the tunica elastica interna than that in the SAH-only and SAH+vehicle groups. Staining for poly(ADP-ribosyl)ation was markedly inhibited in smooth muscle and adventitial cells of the BA in the SAH+3-AB group compared with other groups.

CONCLUSIONS

Inhibiting ADP-ribosylation attenuates cerebral vasospasm after SAH in rabbits, and PARP activation may play an important role in the development of cerebral vasospasm.

Niacinamide therapy for osteoarthritis--does it inhibit nitric oxide synthase induction by interleukin 1 in chondrocytes?

Fifty years ago, Kaufman reported that high-dose niacinamide was beneficial in osteoarthritis (OA) and rheumatoid arthritis. A recent double-blind study confirms the efficacy of niacinamide in OA. It may be feasible to interpret this finding in the context of evidence that synovium-generated interleukin-1 (IL-1), by inducing nitric oxide (NO) synthase and thereby inhibiting chondrocyte synthesis of aggrecan and type II collagen, is crucial to the pathogenesis of OA. Niacinamide and other inhibitors of ADP-ribosylation have been shown to suppress cytokine-mediated induction of NO synthase in a number of types of cells; it is therefore reasonable to speculate that niacinamide will have a comparable effect in IL-1-exposed chondrocytes, blunting the anti-anabolic impact of IL-1. The chondroprotective antibiotic doxycycline may have a similar mechanism of action. Other nutrients reported to be useful in OA may likewise intervene in the activity or synthesis of IL-1. Supplemental glucosamine can be expected to stimulate synovial synthesis of hyaluronic acid; hyaluronic acid suppresses the anti-catabolic effect of IL-1 in chondrocyte cell cultures, and has documented therapeutic efficacy when injected intra-articularly. S-adenosylmethionine (SAM), another proven therapy for OA, upregulates the proteoglycan synthesis of chondrocytes, perhaps because it functions physiologically as a signal of sulfur availability. IL-1 is likely to decrease SAM levels in chondrocytes; supplemental SAM may compensate for this deficit. Adequate selenium nutrition may down-regulate cytokine signaling, and ample intakes of fish oil can be expected to decrease synovial IL-1 production; these nutrients should receive further evaluation in OA. These considerations suggest that non-toxic nutritional regimens, by intervening at multiple points in the signal transduction pathways that promote the synthesis and mediate the activity of IL-1, may provide a substantially superior alternative to NSAIDs (merely palliative and often dangerously toxic) in the treatment and perhaps prevention of OA.

Enhancing the inhibitory effect of nicotinamide upon collagen II induced arthritis in mice using N-acetylcysteine

We could show that both nicotinamide and N-acetylcysteine inhibit collagen induced arthritis in mice. In the present paper, using lower doses of each, we applied combinations of these two substances. We were able to confirm potentiating effects of these combinations. These results may allow new perspectives for the therapy of arthritis to emerge.

Role of poly(ADP-ribose) synthetase in inflammation and ischaemia-reperfusion

Oxidative and nitrosative stress can trigger DNA strand breakage, which then activates the nuclear enzyme poly(ADP-ribose) synthetase (PARS). This enzyme has also been termed poly(ADP-ribose) polymerase (PARP) or poly(ADP-ribose) transferase (pADPRT). Rapid activation of the enzyme depletes the intracellular concentration of its substrate, nicotinamide adenine dinucleotide, thus slowing the rate of glycolysis, electron transport and subsequently ATP formation. This process can result in cell dysfunction and cell death. In this article, Csaba Szabó and Valina Dawson overview the impact of pharmacological inhibition or genetic inactivation of PARS on the course of oxidant-induced cell death in vitro, and in inflammation and reperfusion injury in vivo. A major trigger for DNA damage in pathophysiological conditions is peroxynitrite, a cytotoxic oxidant formed by the reaction between the free radicals nitric oxide and superoxide. The pharmacological inhibition of poly(ADP-ribose) synthetase is a novel approach for the experimental therapy of various forms of inflammation and shock, stroke, myocardial and intestinal ischaemia-reperfusion, and diabetes mellitus.

Enhancement of the effect of methotrexate on collagen II induced arthritis in mice by nicotinamide

Treatment with a combination of 10 mg/kg i.p. methotrexate and 100 mg/kg i.p. nicotinamide inhibits the development of collagen II induced arthritis in male DBA/1 X B.10(4R) mice, as assessed by the arthritic index and whole blood chemiluminescence. The effect is much more pronounced than with either methotrexate or nicotinamide alone at the same concentrations. Determination of GOT and GPT levels in the blood revealed that the treatment causes no toxic side effects on the liver.

Role of poly(ADP-ribose)synthetase in inflammation

Peroxynitrite and hydroxyl radicals are potent initiators of DNA single strand breakage, which is an obligatory stimulus for the activation of the nuclear enzyme poly(ADP-ribose)synthetase (PARS). Rapid activation of PARS depletes the intracellular concentration of its substrate, NAD+, slowing the rate of glycolysis, electron transport and ATP formation. This process can result in acute cell dysfunction and cell necrosis. Accordingly, inhibitors of PARS protect against cell death under these conditions. In addition to the direct cytotoxic pathway regulated by DNA injury and PARS activation, PARS also appears to modulate the course of inflammation by regulating the expression of a number of genes, including the gene for intercellular adhesion molecule 1, collagenase and the inducible nitric oxide synthase. The research into the role of PARS in inflammatory conditions is now supported by novel tools, such as novel, potent inhibitors of PARS, and genetically engineered animals lacking the gene for PARS. In vivo data demonstrate that inhibition of PARS protects against various forms of inflammation, including zymosan or endotoxin induced multiple organ failure, arthritis, allergic encephalomyelitis, and diabetic islet cell destruction. Pharmacological inhibition of PARS may be a promising novel approach for the experimental therapy of various forms of inflammation.

Suppression of type II collagen-induced arthritis by N-acetyl-L-cysteine in mice

1. The antiarthritic and anti-inflammatory efficacy of N-acetyl-L-cysteine (NAC) was tested in male DBA/1 hybrid mice suffering from type II collagen-induced arthritis. Parameters including the arthritis index and the phagocytic responses recorded by chemiluminescence in unseparated blood were used for the assessment of disease activity. 2. Mice were immunized by subdermal injection of bovine type II collagen in Freund's complete adjuvant. The treatment with NAC started at day 42 after immunization and was continued over a period of six weeks: in doses ranging up to 50 mg/kg, a dose-dependent suppression of arthritis was noted; between 50 and 200 mg/kg, the inhibition curve had a plateau [ED50 = 50 mg/(kg x day)]. 3. The arthritis index correlated positively with the generation of chemiluminescence by reactive oxygen species (ROS) produced in neutrophils and monocytes activated by 12-O-tetradecanoylphorbol 13-acetate. 4. After treatment with 100 mg/kg of NAC from day 42 after immunization over a period of six weeks, the ROS production was reduced to levels occurring in whole blood of healthy animals. 5. It is concluded that low-molecular-weight antioxidants such as NAC may be adequate for controlling oxidative stress-derived damage in rheumatic diseases by modulation of ROS-dependent signal transduction pathways.