Increased corticotropin-releasing hormone (CRH) expression in cutaneous lupus lesions.

OBJECTIVE: Corticotropin-releasing hormone (CRH) and pro-opiomelanocortin (POMC) axis activation leads to the production of hormones, such as adrenocorticotrophic hormone (ACTH) and the α-melanocyte stimulating hormone (α-MSH). Data regarding the role of these hormones in systemic lupus erythematosus (SLE) are scarce. In the present study we aim to evaluate the participation of this axis in the cutaneous involvement of SLE. METHODS: Seventeen SLE patients were clinically evaluated, and biopsies from affected and unaffected skin of these patients were compared with 17 healthy control individuals. Immunohistochemical analyses for CRH, ACTH, α-MSH, and MC-1R were performed, and the serum levels of α-MSH, IL-1, IL-1ra, IL-6, IL-10, IL-12p70, IL-17, TNF-α, and IFN-γ were measured. RESULTS: The affected skin of the SLE patients exhibited higher CRH expression in the deep dermis compared to the skin of the controls (p = 0.024), whereas the tissue expression of ACTH, cortisol, α-MSH and its receptor MC-1R were comparable in SLE patients and controls. Higher serum levels of IFN-γ (p = 0.041), TNF-α (p = 0.001) and IL-6 (p = 0.049) were observed in SLE patients compared with controls, while α-MSH levels were similar in both groups. CONCLUSION: The novel finding of elevated CRH expression solely in the affected skin deep dermis supports the notion of a cutaneous local dysfunction of the CRH-POMC axis in the pathogenesis of cutaneous SLE lesions.

Alpha-melanocyte stimulating hormone ameliorates disease activity in an induced murine lupus-like model.

Alpha-melanocyte stimulating hormone (α-MSH) is a neuropeptide exhibiting anti-inflammatory activity in experimental models of autoimmune diseases. However, no studies thus far have examined the effects of α-MSH on systemic lupus erythematosus (SLE). This study aimed to determine the effects of an α-MSH agonist in induced murine lupus. Here we employed female Balb/cAn mice in which lupus was induced by pristane. Groups of lupus animals were treated daily with the α-MSH analogue [Nle4, DPhe7]-α-MSH (NDP-MSH) (1·25 mg/kg) injected intraperitoneally or saline for 180 days. Normal animals comprised the control group. Arthritis incidence, plasma immunoglobulin (Ig)G isotypes, anti-nuclear antibodies (ANA) and plasma cytokines were evaluated. Renal function was assessed by proteinuria and histopathological lesion. Glomerular levels of IgG, α-smooth muscle actin (α-SMA), inducible nitric oxide synthase (iNOS), C3, CD3, melanocortin receptors (MCR)1, corticotrophin-releasing factor (CRF) and α-MSH was estimated by immunohistochemistry. When compared with normal controls, lupus animals exhibited increased arthritis, IgG levels, ANA, interleukin (IL)-6, IL-10, proteinuria and mesangial cell proliferation together with glomerular expression of α-SMA and iNOS. Glomerular expression of MCR1 was reduced in lupus animals. NDP-MSH treatment reduced arthritis scores by 70% and also diminished IgG1 and IgG2a levels and ANA incidence. In the glomerulus, NDP-MSH treatment reduced cellularity by 50% together with reducing IgG deposits, and expression levels of α-SMA, iNOS and CRF were also all decreased. Taken together, our results suggest for the first time that α-MSH treatment improves several parameters of SLE disease activity in mice, and indicate that this hormone is an interesting potential future treatment option.

Effect of topical clay application on the synthesis of collagen in skin: an experimental study.

BACKGROUND: Clay is often used in cosmetic treatments, although little is known about its action. AIM: To evaluate the effect of topical clay application on the histoarchitecture of collagen fibres in rat skin. METHODS: Animals received a daily application of clay and retinoic acid (RA) 0.025% to the dorsal skin over 7 and 14 days, under vaporization at 37 °C for 40 min. Control skin was not vaporized. Samples from each region were excised, and stained with picrosirius red for collagen evaluation. RESULTS: Seven days after clay treatment, an increase in the number of collagen fibres was observed in treated skin compared with control skin (51.74 ± 1.28 vs. 43.39 ± 1.79%, respectively, P < 0.01), whereas RA did not alter the collagen level (45.66 ± 1.10%). Clay application over 14 days did not induce a further increase in skin collagen, whereas treatment with RA did (58.07 ± 1.59%; P = 0.001 vs. control). CONCLUSION: Clay application promotes an increase in the number of collagen fibres, which may account for its beneficial effects.

Nitric oxide modulates lipopolysaccharide-induced endothelial platelet endothelial cell adhesion molecule expression via interleukin-10.

We have shown previously that nitric oxide (NO) controls platelet endothelial cell adhesion molecule (PECAM-1) expression on both neutrophils and endothelial cells under physiological conditions. Here, the molecular mechanism by which NO regulates lipopolysaccharide (LPS)-induced endothelial PECAM-1 expression and the role of interleukin (IL)-10 on this control was investigated. For this purpose, N-(G)-nitro-L-arginine methyl ester (L-NAME; 20 mg/kg/day for 14 days dissolved in drinking water) was used to inhibit both constitutive (cNOS) and inducible nitric oxide (iNOS) synthase activities in LPS-stimulated Wistar rats (5 mg/kg, intraperitoneally). This treatment resulted in reduced levels of serum NO. Under this condition, circulating levels of IL-10 was enhanced, secreted mainly by circulating lymphocytes, dependent on transcriptional activation, and endothelial PECAM-1 expression was reduced independently on reduced gene synthesis. The connection between NO, IL-10 and PECAM-1 expression was examined by incubating LPS-stimulated (1 µg/ml) cultured endothelial cells obtained from naive rats with supernatant of LPS-stimulated lymphocytes, which were obtained from blood of control or L-NAME-treated rats. Supernatant of LPS-stimulated lymphocytes obtained from L-NAME-treated rats, which contained higher levels of IL-10, reduced LPS-induced PECAM-1 expression by endothelial cells, and this reduction was reversed by adding the anti-IL-10 monoclonal antibody. Therefore, an association between NO, IL-10 and PECAM-1 was found and may represent a novel mechanism by which NO controls endothelial cell functions.

A single dose of zoledronic acid reverses the deleterious effects of glucocorticoids on titanium implant osseointegration.

UNLABELLED: This study evaluates the effect of zoledronic acid (ZOL) on the osseointegration of titanium implants in rabbits with glucocorticoid (GC)-induced bone loss, and our findings demonstrated that a single dose of ZOL is able to reverse the detrimental effects of GCs on the osseointegration of titanium implants. INTRODUCTION: The purpose of this study is to evaluate the effect of ZOL on the osseointegration of titanium implants in rabbits with GC-induced bone loss. METHODS: Three groups of six NZW rabbits were treated for 18 weeks with saline (SALINE), GC (methylprednisolone, 0.35 mg/kg three times a week), or GC + ZOL (methylprednisolone + single dose of ZOL, 0.1 mg/kg). The animals received a titanium implant in the left tibia after 6 weeks and were killed at the 18th week. Bone mineral density (BMD) was measured with dual-energy X-ray absorptiometry at baseline, eighth week (W8), and 18th week (W18) after treatment to determine the change upon treatment (BMD). Histomorphometric and serum bone alkaline phosphatase analysis (BAP) were also performed. RESULTS: At W8, GC group had a significant reduction in lumbar spine and tibia BMD compared with SALINE (p = 0.003 and p = 0.000), as also observed for GC + ZOL group (p = 0.014 and p = 0.003) just 2 weeks after ZOL treatment. In contrast, at W18, the GC + ZOL had an evident BMD rescue with similar lumbar spine and tibia BMD compared with SALINE (0.043 +/- 0.006 vs. 0.055 +/- 0.009 g/cm(2), p = 0.457 and 0.027 +/- 0.003 vs. 0.041 +/- 0.011 g/cm(2), p = 0.232) and a significantly higher BMD compared with the GC (p = 0.024 and p = 0.001). Histomorphometry revealed that osseointegration was significantly reduced in GC (tibia cortical thickness and diameter, bone-implant contact, total and peri-implant bone area) whereas GC + ZOL had these parameters similar to SALINE (p > 0.05). Likewise, ZOL reversed the BAP alteration induced by GC. CONCLUSIONS: Our findings demonstrated that a single dose of ZOL is able to reverse the detrimental effects of glucocorticoids on the osseointegration of titanium implants, suggesting that ZOL therapy may improve the outcome of bone implants in patients with glucocorticoid-induced osteoporosis.

Interleukin-18 in chronic joint diseases.

Interleukin-18 is a cytokine member of the IL-1 super family that seems to exert powerful Th1-promoting activities in synergy with IL-12. Here we describe the participation of IL-18 in inflammatory joint diseases, in particular rheumatoid arthritis, adult onset Still's disease and juvenile idiopathic arthritis. The emphasis of this study was to summarize in vivo and in vitro studies that focused the action of this pro-inflammatory cytokine on the arthritic process as well as its role in the complex network of chemical mediators involved.

Inhibition of neutrophil chemotaxis and chemokinesis associated with a plasma protein in aging rats: selective depression of cell responses mediated by complement-derived chemoattractants.

The influence of aging on neutrophil chemotaxis, chemokinesis, and superoxide production was investigated in rats. Animals of two age groups, 3 to 4 months and 20 to 21 months, were used. Equivalent neutrophil chemotactic responses to N-formyl-methionyl-leucyl-phenylalanine (fMLP), leukotriene B4 (LTB4), and bacterial lipopolysaccharide (LPS)-activated plasma were observed in both groups of animals, with cells suspended in Hanks' balanced salt solution (HBSS). However, cross-incubation studies in which cells from young adult rats were exposed to plasma from aged donors, then resuspended in HBSS for testing, showed marked changes in the ability of the cells to respond to the chemoattractants. The response to LPS-activated plasma was reduced, whereas responses to fMLP and LTB4 remained unaltered. Previous incubation of the cells with homologous plasma from young donors produced no effect. The inhibitory activity developing with advancing age affected not only chemotaxis but also random movement stimulated by LPS-activated plasma. The inhibitory activity of chemotaxis and chemokinesis in plasma of aged animals was heat labile (56 degrees C), vanished in the presence of a proteolytic enzyme like trypsin, and was maintained after dialysis with 12,000-Mr retention dialysis tubing. The material did not influence superoxide production by stimulated neutrophils. It is suggested that inhibition of neutrophil locomotion with advancing age is associated with a plasma protein capable of interacting with neutrophil receptors for complement-derived chemoattractants. The inhibitory substance might influence neutrophil responses to infection and inflammation in the elderly.

Role of kinins and nitric oxide on the rabbit arthritis induced by Bothrops jararaca venom.

The effects of the nitric oxide synthase inhibitor N(omega)Nitro-L-arginine-methyl ester (L-NAME) and of the bradykinin B(2) receptor antagonist HOE 140 were evaluated in the inflammatory reaction induced by Bothrops jararaca venom (BjV) in New Zealand White rabbits. Arthritis was induced by injecting 0.5 ml of a sterile solution of BjV (1-64 microg/ml) into the knee intraarticular cavity. The contralateral joint was injected with bovine serum albumin (BSA) diluted in sterile saline. At selected times thereafter (4, 24 and 48 h), the vascular permeability and the leukocyte influx in both the synovial fluid and synovium were evaluated. BjV caused a dose-dependent increase in both leukocyte influx and protein extravasation which reached a maximal response at 16 microg. Bothrops jararaca venom also induced the increase in the leukocyte accumulation in the synovium and in the concentration of both NO(2)/NO(3) in the synovial fluid. Chronic administration of L-NAME (20 mg/kg/day in the drinking water for 2 weeks) markedly reduced the leukocyte accumulation (90%), protein leakage (44%), and NO(2)/NO(3) (50%) levels in the synovial fluid, measured at the 4th h. Hoe 140, given i.v. (0.3 mg/kg, 30 min before) also reduced leukocyte accumulation (75%), protein leakage (48%), and NO(2)/NO(3) (79%) levels in the synovial fluid, measured at the 4th h. Similar results were obtained with acute administration of L-NAME (30 mg/kg, i.v., 30 min before). These results indicate that arthritis induced by BjV is triggered by kinin formation and that the increase in both vascular permeability and leukocyte accumulation is modulated by NO release.

Methotrexate inhibition of bone mineral density increase in growing rabbits: prevention by folinic acid.

OBJECTIVE: Methotrexate (MTX) action on bone metabolism is as yet not completely understood. The results of clinical studies are controversial, since it is difficult to distinguish the side effects of MTX from those of the primary disease. This study assessed the effect of MTX, with and without folinic acid supplementation, on bone mineral density in growing normal rabbits. METHODS: Three groups of young NZW growing female rabbits were treated with: saline (n = 6) or MTX (0.25 mg/kg/week, n = 5) or MTX (same dose as above) plus folinic acid (0.25 mg/kg/week, n = 6) for a period of 3 months. The dose, duration and frequency of MTX administration were similar to the treatment of RA patients. The animals were submitted to dual-energy absorptiometry densitometry (HologicQDR 2000) before and after treatment; total body and L4-L5 BMD were evaluated. Histomorphometric analysis (L4 vertebrae) was also performed. RESULTS: Growing control rabbits showed increased total body BMD from a baseline of 0.180 +/- 0.006 to 0.198 +/- 0.007 gm/cm2 (mean +/- S.E.M, p < 0.006). In contrast, no increase in BMD (0.182 +/- 0.006 versus a baseline of 0.184 +/- 0.004, ns) was observed in the group treated with MTX, while the addition of folinic acid resulted in an increase in BMD values similar to controls, from a baseline of 0.181 +/- 0.004 to 0.198 +/- 0.003, p < 0.02), thus preventing adverse MTX bone effects. Average percent variations in BMD were +7.7%, -1% and +8.4% respectively. Spine (L4-L5) BMD showed analogous results, in line with the histomorphometric data. CONCLUSION: These results strongly support a deleterious action of MTX on bone metabolism, which is prevented by folinic acid supplementation. The potential clinical implications of our data are particularly significant for paediatric therapy.

Action of the 4-nitro-2-phenoximethanesulphonanilide (nimesulide) on neutrophil chemotaxis and superoxide production.

4-nitro-2-phenoximethanesulphonanilide (nimesulide) is a nonsteroidal anti-inflammatory agent that has been employed in the treatment of inflammatory diseases because of its specific actions on the inflammatory response mechanisms caused by injury. The objectives of this paper were to determine the action of this agent on two notable neutrophil functions, chemotaxis and production of the superoxide anion. These two functions were studied after the neutrophils were pre-incubated with three different concentrations of 4-nitro-2-phenoximethanesulphonanilide (0.1; 0.3 and 0.5 mN). The results obtained herein demonstrated that 4-nitro-2-phenoximethanesulphonanilide-exposed peripheral blood neutrophils from healthy subjects produced significantly less superoxide when challenged by phorbolmirystate acetate (PMA at 50 ng/ml) or formy-methionil-leucyl-phenilalanine (FMLP 10-7 M) and opsonizided zymozan (1 mg/ml). Additionally, the agent was equally effective in reducing the PMN chemotoaxis when challenged by C5a factor (2% zimozan activated solution), FMLP 10-9 M and leukotrien (3.10-7 M). The results obtained suggest that in addition to its interference in the metabolism of the aracdonic acid, the 4-nitro-2-phenoximethanesulphonanilide may interfere in a more direct fashion with the neutrophil function. This specific action may contribute to its anti-inflammatory activity.

[Participation of the adhesion molecules in the development of inflammatory response]. / Participação de moléculas de adesão no desenvolvimento da resposta inflamatória.

The authors present a review of adhesion molecules involved in inflammatory response. The recent description of adhesion molecules expressed on circulating leukocytes and endothelial cells, have been elucidated the leukocyte-endothelial interactions, essential for transmigration of leukocytes into tissues. It also indicates how anti-inflammatory drugs affect adhesion molecules. Finally, anti-adhesion therapies are discussed as new strategies for the treatment of inflammatory diseases.

[Role of oxygen free radicals in the physiopathology of rheumatoid arthritis]. / Participação dos radicais livres de oxigênio na fisiopatologia da artrite reumatóide.

The authors present a review of the mechanisms of free radicals production and report the results of "in vivo" and "in vitro" studies correlating these agent with the physiopathologic changes of the rheumatoid arthritis. The data reviewed in this paper support the idea of the participation of free radicals in the articular lesion. However new studies are necessary to determine the contribution of free radicals on disease development, chronicity and the efficacy of antioxidant agents.

Influence of low doses of methotrexate on superoxide anion production by polymorphonuclear leukocytes from patients with rheumatoid arthritis.

OBJECTIVE: The mechanism of methotrexate (MTX) action in rheumatoid arthritis (RA) is unclear. We assessed the influence of MTX on neutrophil superoxide production evaluated by ferricytochrome c reduction. METHODS: Neutrophils were collected from MTX treated patients with RA (MTX-RA), patients with RA without medication (RA) and healthy donors, cocultured with MTX or MTX-RA serum. RESULTS: Polymorphonuclear leukocytes (PMN) from MTX-RA showed decreased superoxide production when compared with cells collected from patients with RA and controls. Control PMN superoxide production was inhibited (36%) by MTX-RA serum incubation. This reduction was accompanied by clinical improvement. MTX had no activity in the in vitro assays. CONCLUSION: MTX treatment may interfere with neutrophil superoxide production.

Low dose methotrexate decreases intraarticular prostaglandin and interleukin 1 levels in antigen induced arthritis in rabbits.

OBJECTIVE: To investigate the effects of methotrexate (MTX) on inflammation variables of antigen induced arthritis (AIA) in rabbits, such as protein leakage to the articular cavity, synovial fluid (SF) leukocyte count, synovial membrane polymorphonuclear (PMN) cell infiltrate, and intraarticular production of eicosanoids and interleukin 1 (IL-1). Dexamethasone and indomethacin were used for comparison. METHODS: NZW rabbits were treated with the following drugs: MTX (0.25 mg/kg), dexamethasone (0.15 mg/kg), indomethacin (4 mg/kg), and sterile saline (control group). All drugs were given by intramuscular route before arthritis was induced and the animals were sacrificed 4 or 24 h later. Leukocyte migration, protein leakage (Evans blue method), synovium PMN cell infiltrate, and intraarticular concentration of prostaglandin E2 (PGE2), thromboxane B2 (TXB2), leukotriene B4 (LTB4) (radioimmunoassay), and IL-1 beta (ELISA) were quantified in SF. RESULTS: Significant reduction of leukocyte migration and protein leakage was observed in the joint fluid of all treated animals. Decrease in the intensity of synovium PMN cell infiltrate also occurred with all treatments. Intraarticular PGE2, TXB2, and IL-1 beta were significantly reduced after 4 h of arthritis induction in animals treated with MTX and dexamethasone. Treatment with indomethacin reduced only PGE2 and TXB2 in SF. Treatments did not change SF IL-1 beta concentration 24 h after arthritis induction. Treatment with dexamethasone increased inflammatory variables and SF LTB4 concentration 24 h after the synovial cavity was challenged with antigen. CONCLUSION: Our results show that MTX, like dexamethasone, reduces the intensity of leukocyte afflux, protein leakage, synovial membrane PMN cell infiltrate, as well as the intraarticular production of PGE2, TXB2, and IL-1 beta in the early phase of antigen induced arthritis in rabbits.

Lymphocytes in non-immune inflammation: a specific subclass of lymphoid cells?

Rats were subjected to various experimental procedures which affected lymphocyte numbers, in an attempt to investigate the participation of individual subpopulations of these cells in the development of acute, non-immune inflammation. Deficient T function, as evidenced in neonatally thymectomized animals, or in 6-week-old animals thymectomized and afterwards exposed to multiple total-body X-ray irradiations, did not interfere with the development of the acute inflammatory responses of the animals to carrageenin. In the former circumstance, the numbers of circulating B lymphocytes, identified by the presence of surface immunoglobulins, were increased. In thymectomized and irradiated rats, the B-lymphocyte subpopulation was reduced. Circumstances causing attenuated inflammatory reactions to carrageenin resulted, first, from lymphocyte depletion by chronic drainage from the thoracic duct and, second, from irradiation of the animals with a single large dose of X-ray, the animals being tested 24 h after irradiation. B lymphocytes in blood remained within the normal range after chronic lymphatic drainage, but a large dose of X-ray markedly reduced their number. In both cases the attenuation of the responses to carrageenin did not seem to be associated with nonspecific hyporeactivity, or with the effect of the treatments on the other blood cells, It is suggested that the development of acute, non-immune inflammation is influenced by lymphoid cells which might constitute a specific subclass of cells, distinct from fully differentiated T and B lymphocytes.

Acute inflammatory responses in rats with protein-calorie malnutrition.

An animal model of protein-calorie malnutrition (PCM) was produced by keeping rats on a protein-free diet during the 13-day interval which followed the period of normal lactation. Malnutrition was characterized by reduction in body weight, in plasma proteins, cholesterol, haemoglobin and leucocyte counts, relative to controls from the same litter receiving a balanced diet. Acute inflammatory responses induced in these animals by carrageenin or staphylococci suspensions, differed markedly from those evoked in matching controls: the resulting oedema developed more slowly and yet persisted for longer intervals; Evans blue, injected i.v., leaked into the inflamed areas in smaller quantities; reduced cell migration to the site of the lesion was observed. The slow development of the response was attributed to the decreased levels of circulating proteins and its persistency to a defective drainage of exuded material. It is concluded that PCM can impair the capacity of response to noxious stimuli, thus rendering the animals more susceptible to infections.

Nitric oxide synthase inhibitor influences prostaglandin and interleukin-1 production in experimental arthritic joints.

OBJECTIVE: To assess involvement of nitric oxide (NO) in the increase in eicosanoid and interleukin- 1 (IL-1) levels in the synovial fluid during antigen-induced arthritis (AIA) in rabbits treated with a competitive inhibitor of NO synthesis. SUBJECTS: Thirteen New Zealand White rabbits were sensitized with 5 mg of methylated bovine serum albumin (mBSA). Arthritis was induced in the knee joint by injecting 0.5 ml of a sterile solution of mBSA (2 mg/ml) into the intra-articular cavity. TREATMENT: Prior to the induction of arthritis, the animals received N-Omega-Nitro-L-Arginine Methyl Ester (LNAME) or N-Omega-Nitro-D-Arginine Methyl Ester (DNAME) for 2 weeks, both at a dose of 20 mg/kg/day mixed with drinking water. METHODS: Leukocyte efflux (total and differential white cell count), vascular permeability (Evans's blue method), synovial PMN cell infiltrate, and total nitrite (NO2.)/nitrate (NO3.) (HPLC), PGE2, TxB2, LTB4 (radioimmunoassay), and IL-1 beta (ELISA) levels were quantified in the synovial fluid. RESULTS: LNAME but not DNAME significantly suppressed leukocyte efflux and protein leakage into the articular cavity as well as synovial PMN cell infiltrate. Total NO2./NO3., PGE2 and IL-1 beta levels were significantly reduced in the synovial fluid of LNAME treated animals. TxB2 and LTB4 were not affected by LNAME treatment. CONCLUSION: These data clearly show NO involvement in the IL-1-induced PGE2 production in the synovial fluid of antigen-induced arthritis in rabbits.

[Intra-articular nitric oxide levels in patients with rheumatoid arthritis]. / Níveis intra-articulares de óxido nítrico em pacientes com doença reumatóide.

The aim of this study was the appraisal of the nitrite and nitrate levels in the synovial fluid of patients with rheumatoid arthritis (RA). The synovial fluid of patients with osteoarthritis (OA) was also evaluated by comparison. Demographic characteristics such as age and sex, and clinical and laboratorial parameters like duration of disease, functional class and erythrocyte sedimentation rate (ESR) were evaluated too. In the synovial fluid of all patients the total and differential leukocyte count, and the nitrite and nitrate levels determined by Griess reaction were analyzed. The results were statistically analyzed by Student's t test and correlation test. We found a significant increase in the intraarticular nitrite and nitrate levels in patients with RA when compared with OA patients (30.68 +/- 2.94 microM x 16.15 +/- 2.73 microM). We did not find any correlation between intraarticular nitrite and nitrate levels and the ESR or the total and differential leukocyte count in the RA synovial fluid. In this study we clearly found an increase in the intraarticular nitrite and nitrate levels in patients with rheumatoid arthritis.

[Role of free radicals in articular inflammatory process]. / Participação dos radicais livres na inflamação articular.

The authors review recent studies supporting the role of free radicals in the inflammatory articular process. More specifically, superoxide anion and its derived active species and nitric oxide are analyzed regarding their generation by the articular cells and tissues, their destructive activity n these specialized tissues. Likewise, effects of the inhibition of free radicals production or activity in the inflammatory process is also commented.

Methotrexate as a preferential cyclooxygenase 2 inhibitor in whole blood of patients with rheumatoid arthritis.

OBJECTIVE: To investigate the regulation of whole-blood cyclooxygenase-1 and -2 (COX-2 and COX-1) activities by methotrexate (MTX) in rheumatoid arthritis (RA) patients. METHODS: Whole blood was withdrawn from nine healthy volunteers, 12 RA patients treated with MTX (RA/MTX) and six RA patients treated with chloroquine (RA/CQ). COX-1 activity was quantified as platelet thromboxane B(2) production in unstimulated blood and COX-2 activity was measured as prostaglandin E(2) (PGE(2)) production in whole blood stimulated with LPS. Thromboxane B(2) and PGE(2) were measured by radioimmunoassay. We studied the drug effect in vitro by direct incubation of MTX with blood obtained from normal donors. Ex vivo assays were performed with blood collected from RA/MTX and RA/CQ patients. The influence of serum factors on enzyme activities was analysed in blood collected from normal donors and incubated with RA/MTX, autologous or heterologous serum. RESULTS: In vitro assays showed no direct action of MTX on the activity of either enzyme. Assays performed with blood from RA/MTX patients showed preferential inhibition of COX-2 activity (PGE(2) = 10.11 +/- 2.42 ng/ml) when compared with blood of normal donors (PGE(2) = 37.7 +/- 4.36 ng/ml; P = 0.001). Inhibition of COX-2 activity was also observed when blood of normal donors was co-incubated with RA/MTX serum. CONCLUSION: Our results clearly show that the anti-inflammatory action of low-dose MTX is partly mediated by a serum factor induced by MTX or a MTX metabolite that preferentially inhibits the activity of COX-2.