Assessment of kininases in rheumatic diseases and the effect of therapeutic agents

Autoimmune-mediated renal disease and hypertension

Hypertension is a major risk factor for cardiovascular disease, chronic kidney disease (CKD), and mortality. Troublingly, hypertension is highly prevalent in patients with autoimmune renal disease and hastens renal functional decline. Although progress has been made over the past two decades in understanding the inflammatory contributions to essential hypertension more broadly, the mechanisms active in autoimmune-mediated renal diseases remain grossly understudied. This Review provides an overview of the pathogenesis of each of the major autoimmune diseases affecting the kidney that are associated with hypertension, and describes the current state of knowledge regarding hypertension in these diseases and their management. Specifically, discussion focuses on Systemic Lupus Erythematosus (SLE) and Lupus Nephritis (LN), Immunoglobulin A (IgA) Nephropathy, Idiopathic Membranous Nephropathy (IMN), Anti-Neutrophil Cytoplasmic Antibody (ANCA)-associated glomerulonephritis, and Thrombotic Thrombocytopenic Purpura (TTP). A summary of disease-specific animal models found to exhibit hypertension is also included to highlight opportunities for much needed further investigation of underlying mechanisms and novel therapeutic approaches.

Upregulation of Proinflammatory Bradykinin Peptides in Systemic Lupus Erythematosus and Rheumatoid Arthritis

Our recent study has implicated bradykinin (BK) signaling as being of pathogenic importance in lupus. This study aims to investigate the biomarker potential of BK peptides, BK and BK-des-arg-9, in lupus and other rheumatic autoimmune diseases. Sera from systemic lupus erythematosus (SLE) patients and healthy subjects were screened for BK and BK-des-arg-9 by liquid chromatography-mass spectrometry metabolomics. Serum from 6-mo-old C57BL/6 mice and three murine lupus strains were also screened for the two peptides by metabolomics. Given the promising initial screening results, validation of these two peptides was next conducted using multiple reaction monitoring in larger patient cohorts. In initial metabolomics screening, BK-des-arg-9 was 22-fold higher in SLE serum and 106-fold higher in mouse lupus serum compared with healthy controls. In validation assays using multiple reaction monitoring and quadrupole time-of-flight mass spectrometry, BK and BK-des-arg-9 showed significant elevations in SLE serum compared with controls (p < 0.0001; area under the curve = 0.79-0.88), with a similar but less pronounced increase being noted in rheumatoid arthritis serum. Interestingly, increased renal SLE disease activity index in lupus patients was associated with reduced circulating BK-des-arg-9, and the reasons for this remain to be explored. To sum, increased conversion of BK to the proinflammatory metabolite BK-des-arg-9 appears to be a common theme in systemic rheumatic diseases. Besides serving as an early marker for systemic autoimmunity, independent studies also show that this metabolic axis may also be a pathogenic driver and therapeutic target in lupus.

Mechanisms of hypertension in autoimmune rheumatic diseases

Patients with autoimmune rheumatic diseases including rheumatoid arthritis and systemic lupus erythematosus have an increased prevalence of hypertension. There is now a large body of evidence showing that the immune system is a key mediator in both human primary hypertension and experimental models. Many of the proposed immunological mechanisms leading to primary hypertension are paralleled in autoimmune rheumatic disorders. Therefore, examining the link between autoimmunity and hypertension can be informative for understanding primary hypertension. This review examines the prevalent hypertension, the immune mediators that contribute to the prevalent hypertension and their impact on renal function and how the risk of hypertension is potentially influenced by common hormonal changes that are associated with autoimmune rheumatic diseases.

Linked Articles

This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc

The renin-angiotensin system in lupus: physiology, genes and practice, in animals and humans

Although multiple studies suggest a potential role for angiotensin II in inflammation, most were performed either in vitro or in animals with non-immune-complex-mediated diseases. Extrapolation of these findings to humans, particularly patients with lupus, which involves multiple immunoregulatory pathways, is unclear. In autoimmune-prone MRL/lpr mice, angiotensin-converting-enzyme (ACE) inhibition improved survival although to a lesser degree than cyclophosphamide and diminished the glomerular histopathologic damage, proteinuria, lymphoid hyperplasia, dermatitis, and hypergammaglobulinemia, with a reduction in TGF-beta1 and beta 2 expression in the kidneys and renal chemokine mRNA expression. Spleen levels of IL-4 and IL-10 were also reduced. Uncontrolled studies in patients with treatment-refractory lupus nephritis showed a significant reduction in proteinuria with ACE-inhibitors and Angiotensin receptor blockers treatment. The ‘masking’ effect of ACE-inhibitors should be taken into consideration, as an exacerbation of lupus nephritis may be missed when estimated by the magnitude of proteinuria, which is decreased by these treatments. No single ACE genotype was consistently associated with subsets of SLE patients. In retrospective analyses, ACE-inhibitor use predicted a favourable outcome in 94 cases of pauci-immune vasculitis. The attenuating effect of angiotensin II inhibitors on the progression of chronic renal disease is well recognized. The data on the role of this intervention in lupus is limited.

Angiotensin-converting enzyme (ACE) serum levels and gene polymorphism in Egyptian patients with systemic lupus erythematosus

Objectives: to investigate the association of angiotensin-converting enzyme (ACE) gene polymorphism and serum ACE level among Egyptian SLE patients and its relation to disease activity parameters. Subjects and methods: we enrolled 50 Egyptian female systemic lupus erythematosus (SLE) patients and 29 healthy controls. Measurement of serum ACE level was done using ELISA, and the ACE genotype was determined by polymerase chain reaction using genomic DNA from peripheral blood. Results: a significant difference was found in ACE genotypes between SLE patients and controls (χ2 = 7.84, p = 0.02). The frequency of ACE DD versus (DI and II) genotypes was significantly higher in SLE patients compared with controls (χ2 = 5.57, p = 0.018 and OR for risk of SLE was 3.1 with 95% confidence interval: 1.198.06). Mean serum ACE level was significantly higher in the SLE group compared with controls ( p = 0.006). Subjects with DD genotype had a significantly higher mean level than those with DI ( p = 0.015) and II genotypes ( p = 0.02). Lupus nephritis patients had a significantly higher frequency of DD versus DI and II genotypes compared with lupus patients without nephritis (Fisher's exact test, p = 0.025) and controls (χ 2 =8.74, p = 0.003). SLE patients with vasculopathy had a significantly higher frequency of DD versus DI/II genotypes compared with SLE patients without vasculopathy (Fisher's exact test, p = 0.04) and controls (χ2 = 9.84 and p = 0.002). Mean serum ACE level was significantly higher in the lupus nephritis and SLE patients with vasculopathy compared with controls ( p = 0.008, p = 0.001, respectively). Significant positive correlations were found between serum ACE level and serum creatinine and 24 h proteinuria ( p = 0.03, 0.009, respectively). SLE patients with DD genotype had a statistically significant higher mean SLEDAI score than those with (DI/II) genotypes ( p = 0.02). Significant positive correlation was found between serum ACE levels and SLEDAI scores ( p = 0.04). Conclusion: ACE genotype and subsequently serum ACE level could be associated with the disease activity of Egyptian SLE patients; in addition, ACE deletion polymorphism might be used as one of the predictive factors for the activity of SLE. Further studies on a larger number of patients should be done to determine the exact prevalence of ACE gene polymorphism among Egyptian SLE patients.

Kallikreins, kininogens and kinin receptors on circulating and synovial fluid neutrophils: role in kinin generation in rheumatoid arthritis

OBJECTIVES

Neutrophils traffic into and have the capacity to generate kinins in SF of RA patients. The aim of this study was to assess the expression of kallikreins, kininogens and kinin receptors in circulating and SF neutrophils, as well as synovial tissue of RA patients, and to assess kinin generation in SF.

METHODS

Neutrophils were isolated from blood and SF of RA patients and blood of healthy volunteers. Expression of kallikreins, kininogens and kinin receptors in neutrophils and synovial tissue was assessed by immunocytochemistry using specific antibodies, with visualization by brightfield and confocal microscopy. Levels of basal and generated kinins in SF of RA patients were measured by ELISA.

RESULTS

Kinin labelling was significantly reduced, indicating the loss of the kinin moiety from kininogen on circulating (P < 0.001) and SF neutrophils (P < 0.05) of RA patients. Immunolabelling of tissue kallikrein was also decreased, whereas kinin B(1) and B(2) receptor expression was increased in circulating and SF neutrophils of RA patients. Immunolabelling of kallikreins and kinin receptor proteins was similar in RA and normal synovial tissues. The basal kinin level in SF of RA patients was 5.7 +/- 6.1 ng/ml and the mean concentration of kinins generated in vitro was 80.6 +/- 56.3 ng/ml. The capacity for kinin generation was positively correlated with measures of disease activity.

CONCLUSIONS

Kallikrein-kinin proteins on neutrophils play an important role in kinin generation and the pathophysiology of RA. Specific kallikrein and kinin receptor antagonists may be useful as IA therapies for inflamed joints.

The pathophysiology of hypertension in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune inflammatory disorder that predominantly affects women during their reproductive years. Although SLE can affect any organ system, the kidneys are prominently involved in the form of immune complex glomerulonephritis. In addition, in women with SLE, risk for the development of cardiovascular disease is dramatically increased. Hypertension is a major risk factor for cardiovascular disease and is highly prevalent in women with SLE. Nevertheless, there has been little exploration of the pathophysiological mechanisms that promote SLE hypertension. This review discusses the role of several mechanisms, with an emphasis on the kidney, in SLE hypertension. These mechanisms include the renin-angiotensin system, endothelin, oxidative stress, sex steroids, metabolic changes, peroxisome proliferator-activated receptor-gamma, and, perhaps most importantly, chronic inflammation and cytokines. Growing evidence suggests a link between chronic inflammation and hypertension. Therefore, elucidation of mechanisms that promote SLE hypertension may be of significant value not only for patients with SLE, but also for a better understanding of the basis for essential hypertension.

High abundance synovial fluid proteome: distinct profiles in health and osteoarthritis

The development of increasingly high-throughput and sensitive mass spectroscopy-based proteomic techniques provides new opportunities to examine the physiology and pathophysiology of many biologic fluids and tissues. The purpose of this study was to determine protein expression profiles of high-abundance synovial fluid (SF) proteins in health and in the prevalent joint disease osteoarthritis (OA). A cross-sectional study of 62 patients with early OA (n = 21), patients with late OA (n = 21), and control individuals (n = 20) was conducted. SF proteins were separated by using one-dimensional PAGE, and the in-gel digested proteins were analyzed by electrospray ionization tandem mass spectrometry. A total of 362 spots were examined and 135 high-abundance SF proteins were identified as being expressed across all three study cohorts. A total of 135 SF proteins were identified. Eighteen proteins were found to be significantly differentially expressed between control individuals and OA patients. Two subsets of OA that are not dependent on disease duration were identified using unsupervised analysis of the data. Several novel SF proteins were also identified. Our analyses demonstrate no disease duration-dependent differences in abundant protein composition of SF in OA, and we clearly identified two previously unappreciated yet distinct subsets of protein profiles in this disease cohort. Additionally, our findings reveal novel abundant protein species in healthy SF whose functional contribution to SF physiology was not previously recognized. Finally, our studies identify candidate biomarkers for OA with potential for use as highly sensitive and specific tests for diagnostic purposes or for evaluating therapeutic response.

Circulating activities of angiotensin-converting enzyme, its homolog, angiotensin-converting enzyme 2, and neprilysin in a family study

The renin-angiotensin system is a key regulator of blood pressure (BP), with inhibitors of angiotensin-converting enzyme (ACE) used clinically to treat hypertension and other cardiovascular conditions. ACE2 is a newly identified member of this system, which converts angiotensin II to angiotensin, and of which the occurrence in plasma has not been investigated. The aim of this study was to determine the heritability of circulating ACE, ACE2, and neprilysin (NEP), which may also be a regulator of BP, in a family study, and to determine covariates that contribute to the variation in plasma activity. ACE, ACE2, and NEP activities were measured in plasma from 534 subjects in the Leeds Family Study using selective fluorogenic substrates. Genetic factors accounted for 24.5%, 67%, and 22.7% of the phenotypic variation in circulating ACE, ACE2, and NEP, respectively. ACE insertion/deletion polymorphism and other measured covariates accounted for 23.8% of variance in circulating ACE. High-density lipoprotein cholesterol was a significant determinant of circulating ACE2. Measured covariates accounted for 17.3% of variation in circulating NEP. ACE and NEP were associated with systolic and diastolic BP in univariate analyses; however, only ACE was independently associated with systolic and diastolic BP after accounting for covariates and shared childhood household.

Renin and angiotensin-converting enzyme (ACE) as active components of the local synovial renin-angiotensin system in rheumatoid arthritis

Local functional renin-angiotensin systems (RAS) have been demonstrated in many organ and tissue systems. Angiotensins, the effector growth factors of the RAS, are essentially cytokines and growth factors which actively contribute to many inflammatory reactions. Among the components of RAS, angiotensin-converting enzyme (ACE) and renin have been previously investigated separately in RA. In this study, ACE levels and renin concentrations were measured in the sera of 16 patients with RA (median age: 45 (26-69), male/female: 3/13), 13 patients with osteoarthritis (OA) (median age: 55 (28-72), male/female: 5/8), and 11 healthy adults (median age: 44 (35-70), male/female: 6/5). Synovial ACE levels and renin concentrations were also measured concurrently in patients with RA and OA. Serum ACE levels were comparable between the groups. However, synovial fluid ACE levels were significantly higher in the patients with RA than in patients with OA. Likewise, synovial fluid renin concentrations were higher in RA patients than in OA patients, while serum renin concentrations were similar in patients with RA and OA and in healthy controls. Moreover, there was a significant negative correlation between the duration of the disease and synovial renin concentrations in RA patients. In conclusion, locally-generated active renin and ACE could contribute to joint destruction in rheumatoid arthritis.

Angiotensin-converting enzyme gene polymorphism and vascular manifestations in Korean patients with SLE

Systemic lupus erythematosus (SLE) is an inflammatory multisystem disease of unknown etiology with immunologic aberrations. Many studies have shown that genetic and environmental factors are implicated in the development of SLE. Angiotensin-converting enzyme (ACE) affects various immune phenomena through the renin-angiotensin and kallikrein-kininogen systems by creating angiotensin II and inactivating bradykinin. We investigated the correlation between insertion/ deletion polymorphism of the ACE gene and the clinical manifestations of SLE, especially vascular involvement and lupus nephritis. Two-hundred and eleven Korean patients fulfilling the ACR criteria and 114 healthy subjects were enrolled. The ACE genotype was determined by polymerase chain reaction using genomic DNA from peripheral blood. The nephritis patients were classified by the WHO classification. In addition, the activity and chronicity index were used to assess the severity of renal involvement. We evaluated vascular involvement by the presence or absence of hypertension, Raynaud's phenomenon, livedo reticularis, antineutrophil cytoplasmic antibody and the SLICC/ACR Damage Index. The gene frequency of ACE gene polymorphism was as follows: II 39 vs 34%, ID 41 vs 50%, DD 20 vs 16% in SLE patients and controls, respectively. There was no difference in genotype frequency between both groups. There were no significant differences between the distribution of ACE gene genotypes and lupus nephritis and its related parameters, including WHO classification, activity index, chronicity index, renal dysfunction and amount of 24 h urinary protein. The ACE genotypes and alleles did not affect the presence of vascular manifestations evaluated, but the frequency of DD genotype was significantly low in SLE patients with Raynaud's phenomenon compared to those without Raynaud's phenomenon (P = 0.002 for ACE ID vs DD and II, OR 2.7, 95% CI 1.43-5.09; P=0.023 for ACE DD vs ID and II, OR 0.33, 95% CI 0.12-0.89). Also skewing from DD to II genotype was noted in patients with anti-Sm antibody compared to those without anti-Sm antibody (P = 0.025 for ACE DD vs ID and II, OR 0.21, 95% CI 0.05-0.93). The onset age of serositis was older in patients with the ID genotype than the others (ID= 34.5+/-10.8, II + DD = 25.6+/-10.2, P= 0.002). Also the onset age of malar rash was older in patients with II genotype than the others (II=26.7+/-8.4, ID+DD=21.3+/-9.0; P=0.021). The patients with I allele showed a significantly higher frequency of serositis (P = 0.022). Taken together, the I/D polymorphisms of ACE gene did not affect susceptibility of SLE, lupus nephritis and the vascular manifestations, including Raynaud's phenomenon, in Korean SLE patients, although the DD genotype was negatively associated with Raynaud's phenomenon among SLE patients. However, it would be valuable to evaluate the role of other genes potentially related to vascular events, such as endothelin, nitric oxide or angiotensin II receptor as well as ACE gene.

Kinin system in lupus nephritis

There are few studies regarding the evaluation of the kinin system in patients with systemic lupus erythematosus (SLE). In this study, we evaluated the plasma levels of high-molecular weight kininogen (HKg), low-molecular weight kininogen (LKg) and plasma kallikrein; the plasma activity of tissue kallikrein and kininase II, and urinary kallikrein and kininase II activities in patients presenting with active lupus nephritis. A total of 30 patients (29 women) aged 21-62 years (median = 39) and 30 controls matched to the patients for sex and age were studied. Patients presenting with other underlying diseases or using drugs, which could interfere with the kinin system, were excluded. HKg and LKg levels were indirectly evaluated by ELISA. Plasma kallikrein, tissue kallikrein, and kininase II were evaluated by their enzymatic activity on selective substrates. The Mann-Whitney test was used for statistical analysis. HKg, LKg and plasma kallikrein levels were significantly increased in patients (p < 0.001, for each comparison). Similarly, tissue kallikrein and kininase II activities were significantly increased in plasma and urine of patients (p <0.001, for each comparison). In urine, the activities of tissue kallikrein and kininase II were at least seven times higher than those seen in the plasma of patients. These results indicate that the kinin system is involved in the acute manifestations of lupus nephritis. Kinins may facilitate immunecomplex deposition and may induce the release of other pro-inflammatory mediators, including cytokines actively involved in the pathogenesis of lupus nephritis.

Generation of kinins in synovial fluid from patients with arthropathy

An enzyme-linked immunosorbent assay method is described for the measurement of kinin formation in synovial fluid from patients with rheumatoid and osteoarthritis (RA and OA). Basal kinin concentrations were less than 6 ng/ml in synovial fluid collected in the presence of inhibitors of kinin forming (kininogenase) and kinin metabolising (kininase) enzymes. During incubation of synovial fluid in the presence of kininase inhibitors alone, kinins were produced rapidly over the first 10 min, but production ceased completely within 30 min due to inhibition of the endogenous kininogenases; the rate of kinin generation during the early rapid phase correlated well with the plateau kinin concentration. Plateau kinin levels in synovial fluid from 15 patients with OA and RA ranged from 98 to 427 ng/ml, with a median value of 148 ng/ml. This study demonstrates clearly that synovial fluid from arthritis patients has the capacity to produce kinins. Although the number of patients was small, the amount of kinin generated in vitro varied over a wide range and a relationship between intra-articular kinin formation and clinical features may become apparent in a larger group of patients. The technique could also be used to investigate other biological systems in which a role has been proposed for kinins.

Auranofin and its combination with LTB4 influences ATP level and migration of human polymorphonuclear cells in vitro

Auranofin (AF), an orally administered antirheumatic drug, reduces the ATP level of PMN cells in vitro in a dose-dependent manner and provokes various effects on PMN migration. Under the experimental conditions, AF in concentrations between 10(-8) M and 10(-3) M produced a statistically significant (P < 0.05) dose-related reduction in ATP level, which ranged from 89% of the control value with 10(-8) M AF to 46.8% of the control with 10(-3) M AF. On the other hand, the combination of AF and the chemoattractant LTB4 (1 ng/ml) shows agonistic effects on the intracellular ATP level. AF at 10(-5) M significantly increases the ATP (33%; P < 0.03). In general migration of PMN cells is stimulated by 10(-7) M AF [chemotactic index (CI) = 1.26], but inhibited by 10(-5) M (CI = 0.65), 10(-4) M (CI = 0.09) and 10(-3) M AF (CI = 0.01). These effects were statistically significant at P < 0.05. In the presence of LTB4 (1 ng/ml), which resulted in an average CI of 2.9, AF also inhibits the chemotactic effect of the chemoattractant, with the CI being significantly reduced at 10(-6) M AF (CI = 2.3) and 10(-4) M AF (CI = 0.05). In the latter case the effect was also confirmed by the leading-front technique. AF at 10(-6) M is a level that could be reached in the blood after continuous therapy regimens, and these results are therefore of practical interest. They expand our knowledge of the effects of AF on PMN cells, whereby reducing effects on intracellular ATP were observed with AF alone and stimulating effects in combination with LTB4. With low AF concentrations, the reduction of the ATP level is only a part of its action that seems to be independent of its effect on cell migration and chemotaxis.

The role of bradykinin B1 receptors in the maintenance of intra-articular plasma extravasation in chronic antigen-induced arthritis

1. The role of bradykinin B1 and B2 receptors in bradykinin- and des-Arg9-bradykinin-induced plasma extravasation in normal and inflamed rat knee joints was investigated by use of an antigen-induced model of chronic arthritis. A modification of an Evans blue extraction technique allowed the unstimulated (basal) plasma extravasation to be assessed in this model. The contributions of bradykinin B1 and B2 receptors towards basal synovial plasma extravasation were determined. 2. In normal knees, intra-articular injection of bradykinin (BK) induced plasma extravasation in a potent, dose-dependent manner with a threshold of 0.01 nmol and an ED50 of 0.1 nmol. In day 5 arthritic knees, basal plasma extravasation was substantially enhanced. Lower doses of BK had no demonstrable effect and increases above basal extravasation were first observed at 0.1 nmol. Thereafter the dose-response mirrored the response in normal knees and the maximal response was unaltered. 3. The B1 agonist, des-Arg9-BK, induced slight but significant plasma extravasation in normal knees but was less potent than bradykinin. This response was inhibited by the B1 receptor antagonist, des-Arg9, [Leu8]-BK. Lower doses of des-Arg9-BK bradykinin did not significantly increase basal extravasation in day 5 arthritic knees but, in contrast to BK, the maximal response was significantly enhanced. 4. The B2 antagonist, Hoe 140, inhibited BK-induced plasma extravasation in normal joints over a dose-range of 0.1-1.0 nmol but was relatively inactive in day 5 inflamed knees. The B1 receptor antagonist, des-Arg9, [Leu8]-BK, was relatively inactive in normal joints but showed increased potency against BK-induced plasma extravasation in day 5 arthritic joints.5. Hoe 140 and des-Arg9,[Leu8]-BK both inhibited basal extravasation in arthritic joints on days 1 and 5 post-challenge in a dose-dependent fashion. Whilst Hoe 140 was the more potent inhibitor on day 1, it was less potent than des-Arg9,[Leu8]-BK on day 5.6. Although the majority of responses to BK in normal tissue are mediated via B2 receptors, a small population of B1 receptors may exist in normal joint tissues. The data presented in this study suggest an evolving role for B1 receptors in the mediation of plasma extravasation in inflamed joint tissues. A role for BK antagonists in the treatment of arthritis is also suggested.

Metabolism and characterisation of kinins and Hoe 140 (kinin antagonist) in the synovial fluid of patients with inflammatory joint diseases

Methods have been optimised for the collection of synovial fluid and the chromatographic separation of individual kinins (bradykinin and kallidin) in the fluid by HPLC. In addition, the stability of the kinin antagonist, Hoe 140, in synovial fluid was compared with that of synthetic bradykinin. Although bradykinin was completely degraded after incubation for only 6 h in pooled synovial fluid obtained from patients with rheumatoid arthritis, Hoe 140 was stable for as long as 2 weeks under the same conditions. These studies will provide quantitative information regarding levels of kinins in inflamed joints and an insight into the therapeutic potential of kinin antagonists.

D-penicillamine

D-Pen represents an effective treatment for a proportion of patients with RA and PSS. Its status in the treatment of juvenile RA is uncertain. The best results will be obtained by a skillful, careful physician maintaining careful surveillance for toxicity. Neither the mode of action nor the mechanisms of toxicity are well understood in RA. Consequently, safer and more effective analogues of D-pen have not been produced.

Spontaneous release of angiotensin converting enzyme and interleukin 1 beta from peripheral blood monocytes from patients with rheumatoid arthritis under a serum free condition

Angiotensin converting enzyme (ACE) and interleukin 1 activities were assayed simultaneously in the serum free medium from the unstimulated peripheral blood monocytes from 32 patients with rheumatoid arthritis (RA), 11 patients with osteoarthritis, and 25 normal controls matched for age and sex. Angiotensin converting enzyme activity was raised in most (29/32) patients with RA and interleukin 1 activity (most of which was interleukin 1 beta) was enhanced in 11/32 patients with RA, while monocytes from only two patients with osteoarthritis, but from none of the controls, secreted a small amount of ACE alone in the culture condition. Monocytes from patients with early RA (disease duration less than 3 years) released significantly more ACE and interleukin 1 than those from late stage RA (disease duration greater than or equal to 3 years).