Hypothalamic-pituitary-adrenal axis regulation of inflammation in rheumatoid arthritis

Voluntary wheel running from early adolescence reduces disease progression, and anxiety- and depression-related symptoms in an adult male mouse model of rheumatoid arthritis

Rheumatoid arthritis (RA) is a multifactorial autoimmune disease that progressively destroys synovial joints and leads to chronic systemic inflammation. This autoimmune disorder is associated with increased anxiety- and depression-related symptoms, which reduces quality of life. Clinical and experimental evidence suggests that higher physical activity from early adolescence may prevent chronic diseases and reduce the risk of mental health problems in adulthood. This study aimed to assess whether voluntary wheel running from early adolescence can decrease clinical symptoms, anxiety- and depression-related behaviors in adult mice with rheumatoid arthritis. Adolescent male mice were exposed to voluntary wheel running until adulthood and got collagen-induced arthritis. We measured body weight, the thickness of the hind paw and knee joint (clinical signs), anxiety- and depression-related behaviors, serum testosterone, and cytokines (IFN-γ IL-1β, IL-6, TNF-α, IL-10). The findings showed that collagen-induced arthritis resulted in anxious-like behavior, increased anhedonia, elevated IL-6, IL-1β, TNF-α, and IFN-γ, and decreased testosterone levels in the serum of mice. However, no change was observed in behavioral despair. We found that higher physical activity from early adolescence significantly reduced the severity of clinical signs, anxiety- and anhedonia-like behaviors, and decreased behavioral despair in RA-induced mice. In addition, the running wheel exposure normalized RA-induced abnormalities in testosterone and inflammatory cytokines in mice. Altogether, this study suggests that higher physical activity from early adolescence may make mice less vulnerable or resistant to RA-induced clinical symptoms and anxiety- and depression-related behaviors by changing testosterone and inflammatory cytokines productions in adulthood.

Neuromodulation as a Potential Disease-Modifying Therapy for Osteoarthritis

PURPOSE OF REVIEW

The following review discusses the therapeutic potential of targeting the autonomic nervous system (ANS) for osteoarthritis (OA) treatment and encourages the field to consider the candidacy of bioelectronic medicine as a novel OA treatment strategy.

RECENT FINDINGS

The study of OA pathogenesis has focused on changes occurring at the joint level. As such, treatments for OA have been aimed at the local joint environment, intending to resolve local inflammation and decrease pain. However, OA pathogenesis has shown to be more than joint wear and tear. Specifically, OA-related peripheral and central sensitization can prompt neuroplastic changes in the nervous system beyond the articular joint. These neuroplastic changes may alter physiologic systems, like the neuroimmune axis. In this way, OA and related comorbidities may share roots in the form of altered neuroimmune communication and autonomic dysfunction. ANS modulation may be able to modify OA pathogenesis or reduce the impact of OA comorbidities. Moreover, blocking chronic nociceptive drive from the joint may help to prevent maladaptive nervous system plasticity in OA.

Inflammation-related biomarkers in major psychiatric disorders: a cross-disorder assessment of reproducibility and specificity in 43 meta-analyses

Inflammation is a natural defence response of the immune system against environmental insult, stress and injury, but hyper- and hypo-inflammatory responses can trigger diseases. Accumulating evidence suggests that inflammation is involved in multiple psychiatric disorders. Using inflammation-related factors as biomarkers of psychiatric disorders requires the proof of reproducibility and specificity of the changes in different disorders, which remains to be established. We performed a cross-disorder study by systematically evaluating the meta-analysis results of inflammation-related factors in eight major psychiatric disorders, including schizophrenia (SCZ), bipolar disorder (BD), autism spectrum disorder (ASD), major depression disorder (MDD), post-trauma stress disorder (PTSD), sleeping disorder (SD), obsessive-compulsive disorder (OCD) and suicide. A total of 43 meta-analyses involving 704 publications on 44 inflammation-related factors were included in the study. We calculated the effect size and statistical power for every inflammation-related factor in each disorder. Our analyses showed that well-powered case-control studies provided more consistent results than underpowered studies when one factor was meta-analysed by different researchers. After removing underpowered studies, 30 of the 44 inflammation-related factors showed significant alterations in at least one disorder based on well-powered meta-analyses. Eleven of them changed in patients of more than two disorders when compared with the controls. A few inflammation-related factors showed unique changes in specific disorders (e.g., IL-4 increased in BD, decreased in suicide, but had no change in MDD, ASD, PTSD and SCZ). MDD had the largest number of changes while SD has the least. Clustering analysis showed that closely related disorders share similar patterns of inflammatory changes, as genome-wide genetic studies have found. According to the effect size obtained from the meta-analyses, 13 inflammation-related factors would need <50 cases and 50 controls to achieve 80% power to show significant differences (p < 0.0016) between patients and controls. Changes in different states of MDD, SCZ or BD were also observed in various comparisons. Studies comparing first-episode SCZ to controls may have more reproducible findings than those comparing pre- and post-treatment results. Longitudinal, system-wide studies of inflammation regulation that can differentiate trait- and state-specific changes will be needed to establish valuable biomarkers.

Neuroendocrine and neurophysiological effects of interleukin 6 in rheumatoid arthritis

RA is a chronic, systemic, autoimmune disease characterized by inflammation and degradation of the joints, causing significant negative impact on quality of life. In addition to joint disease, symptoms and co-morbidities associated with RA-namely pain, fatigue and mood disorders-are often as debilitating as the disease itself. The pro-inflammatory cytokine IL-6 plays a critical role in RA-associated pathology. However, a greater understanding of the translational effects of IL-6 outside of the immune system is needed. This review discusses our current understanding of emerging aspects of IL-6 in RA-associated pain, fatigue and mood disorders such as depression and anxiety. This review also describes the clinical effects of IL-6 inhibition on these symptoms and co-morbidities in patients with RA.

Magnocellular Vasopressin and the Mechanism of "Glucocorticoid Escape"

It is now widely accepted that magnocellular vasopressinergic neurons in the supraoptic and paraventricular nuclei participate in the control of adrenocorticotropin secretion by the anterior pituitary gland. However, it remains to be explored in further detail, when and how these multifunctional neurons are involved in the control of anterior pituitary function. This paper highlights the role of magnocellular vasopressin in the hypothalamic pituitary adrenocortical axis with special reference to escape from glucocorticoid feedback inhibition. The signaling mechanisms underlying glucocorticoid escape by pituitary corticotrope cells, as well as the wider physiologic and pathologic contexts in which escape is known to occur-namely strenuous exercise, and autoimmune inflammation will be considered. It is proposed that by inducing escape from glucocorticoid feedback inhibition at the pituitary level, magnocellular vasopressin is critically important for the anti-inflammatory, and immunosuppressant actions of endogenous corticosteroids.

Stress axis variability is associated with differential ozone-induced lung inflammatory signaling and injury biomarker response

Ozone (O₃), a ubiquitous urban air pollutant, causes adverse pulmonary and extrapulmonary effects. A large variability in acute O₃-induced effects has been observed; however, the basis for interindividual differences in susceptibility is unclear. We previously demonstrated a role for the hypothalamic-pituitary-adrenal (HPA) stress axis and glucocorticoid response in acute O₃ toxicity. Glucocorticoids have important anti-inflammatory actions, and have been shown to regulate lung inflammatory responses. We hypothesised that a hyporesponsive HPA axis would be associated with greater O₃-dependent lung inflammatory signaling. Two genetically-related rat strains with known differences in stress axis reactivity, highly-stress responsive Fischer (F344) and less responsive Lewis (LEW), were exposed for 4 h by nose-only inhalation to clean air or 0.8 ppm O₃, and euthanized immediately after exposure. As expected, baseline (air-exposed) plasma corticosterone was significantly lower in the hypo-stress responsive LEW. Although O₃ exposure increased plasma corticosterone in both strains, corticosterone remained significantly lower in LEW when compared to F334. LEW exhibited greater O₃-induced inflammatory cytokine/chemokine signaling compared to F344, consistent with the lower corticosterone levels. Since we observed strain-specific differences in inflammatory signaling, we further investigated injury biomarkers (total protein, albumin and lactate dehydrogenase). Although the hyper-responsive F344 exhibited lower inflammatory signaling in response to O₃ compared with LEW, they had greater levels of lung injury biomarkers. Our results indicate that stress axis variability is associated with differential O₃-induced lung toxicity. Given the large variability in stress axis reactivity among humans, stress axis regulation could potentially be a determining factor underlying O₃ sensitivity.

Intra-articular glucocorticoid injections and their effect on hypothalamic-pituitary-adrenal (HPA)-axis function

The use of intra-articular (IA) glucocorticoids for reducing pain and inflammation in patients with osteoarthritis, rheumatoid arthritis, and other inflammatory arthropathies is widespread among primary care physicians, specialists, and non-specialists in the United States. Injectable glucocorticoids have anti-inflammatory and analgesic properties which can be effective in improving clinical parameters such as pain, range of motion, and quality of life. After injection into the IA space, glucocorticoids may be systemically absorbed; the degree of absorption can depend on the size of the joint injected, the injectable glucocorticoid preparation used, the dosage, and the frequency of the injection. The adverse effects of intra-articular glucocorticoid injections (IAGC) can often be overlooked by both the patient and physicians who administer them, in particular the potential deleterious effect on the hypothalamic-pituitary-adrenal (HPA)-axis which can result in adrenal suppression and/or iatrogenic Cushing syndrome. In this paper we provide an overview on the often under-recognized effects of IAGC on HPA-axis function.

Rodent models of ischemic stroke lack translational relevance... are baboon models the answer?

Rodent models of ischemic stroke are associated with many issues and limitations, which greatly diminish the translational potential of these studies. Recent studies demonstrate that significant differences exist between rodent and human ischemic stroke. These differences include the physical characteristics of the stroke, as well as changes in the subsequent inflammatory and molecular pathways following the acute ischemic insult. Non-human primate (NHP) models of ischemic stroke, however, are much more similar to humans. In addition to evident anatomical similarities, the physiological responses that NHPs experience during ischemic stroke are much more applicable to the human condition and thus make it an attractive model for future research. The baboon ischemic stroke model, in particular, has been studied extensively in comparison to other NHP models. Here we discuss the major shortcomings associated with rodent ischemic stroke models and provide a comparative overview of baboon ischemic stroke models. Studies have shown that baboons, although more difficult to obtain and handle, are more representative of ischemic events in humans and may have greater translational potential that can offset these deficiencies. There remain critical issues within these baboon stroke studies that need to be addressed in future investigations. The most critical issue revolves around the size and the variability of baboon ischemic stroke. Compared to rodent models, however, issues such as these can be addressed in future studies. Importantly, baboon models avoid many drawbacks associated with rodent models including vascular variability and inconsistent inflammatory responses - issues that are inherent to the species and cannot be avoided.

Anti-inflammatory glucocorticoid drugs: reflections after 60 years

This review considers the problem of the serious concomitant side effects of powerful anti-inflammatory drugs modelled upon the principal human glucocorticoid hormone, cortisol. The very nature of the original bio-assays to validate their cortisol-like hormonal and anti-inflammatory activities ensured that pleiotropic toxins were selected for clinical studies. Other complicating factors have been (1) considerable reliance on bio-assays conducted in laboratory animals that primarily secrete corticosterone, not cortisol, as their principal anti-inflammatory adrenal hormone; (2) some differences in the binding of xenobiotic cortisol analogues (vis á vis cortisol) to transport proteins, detoxifying enzymes and even some intra-cellular receptors; (3) the "rogue" properties of these hormonal xenobiotics, acting independently of--but still able to suppress--hormonal mechanisms regulating endogenous cortisol; and (4) problems of intrinsic/acquired "steroid resistance", diminishing their clinical efficacy, but not necessarily all their toxicities. The rather gloomy conclusion is that devising new drugs to reproduce the effect of multi-potent hormones may be a recipe for disaster, in contexts other than simply remedying an endocrine deficiency. Promising new developments include "designed" combination therapies that allow some reduction in total steroid doses (and hopefully their side effects); sharpening strategies to limit the actual duration of steroid administration; and resurgent interest in searching for more selective analogues (both steroidal and non-steroid) with less harmful side effects. Some oversights and neglected areas of research are also considered. Overall, it now seems timely to engage in some drastic rethinking about (retaining?) these "licensed toxins" as fundamental therapies for chronic inflammation.

Different strokes for different folks: the rich diversity of animal models of focal cerebral ischemia

No single animal model is able to encompass all of the variables known to affect human ischemic stroke. This review highlights the major strengths and weaknesses of the most commonly used animal models of acute ischemic stroke in the context of matching model and experimental aim. Particular emphasis is placed on the relationships between outcome and underlying vascular variability, physiologic control, and use of models of comorbidity. The aim is to provide, for novice and expert alike, an overview of the key controllable determinants of experimental stroke outcome to help ensure the most effective application of animal models to translational research.

11beta-Hydroxysteroid dehydrogenase type 1 is an important regulator at the interface of obesity and inflammation

Systemic glucocorticoid excess, as exemplified by the Cushing syndrome, leads to obesity and all further symptoms of the metabolic syndrome. The current obesity epidemic, however, is not characterized by increased plasma cortisol concentrations, but instead comes along with chronic low-grade inflammation in adipose tissue and concomitant increased levels of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1, gene HSD11B1), a parameter known to cause obesity in a mouse model. 11beta-HSD1 represents an intracellular amplifier of active glucocorticoid, thus enhances the associated effects on the inflammatory response as well as on nutrient and energy metabolism, and may therefore cause and exacerbate obesity by local increase of glucocorticoid concentrations. Obtained by extensive literature and database searching, the present review includes comprehensive lists of primary glucocorticoid-sensitive genes and gene products as well as of the thus far known regulators of HSD11B1 expression with implication in inflammation and metabolic disease. Collectively, the data clearly show that, in addition to amplifying active glucocorticoid and thus profoundly modulating inflammation and nutrient metabolism, 11beta-HSD1 is subject to tight control of multiple additional immunomodulatory and metabolic regulators. Hence, 11beta-HSD1 acts at the interface of inflammation and obesity and represents an efficient integrator and effector of local inflammatory and metabolic state.

Differential expression, function and response to inflammatory stimuli of 11beta-hydroxysteroid dehydrogenase type 1 in human fibroblasts: a mechanism for tissue-specific regulation of inflammation

Stromal cells such as fibroblasts play an important role in defining tissue-specific responses during the resolution of inflammation. We hypothesized that this involves tissue-specific regulation of glucocorticoids, mediated via differential regulation of the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). Expression, activity and function of 11β-HSD1 was assessed in matched fibroblasts derived from various tissues (synovium, bone marrow and skin) obtained from patients with rheumatoid arthritis or osteoarthritis. 11β-HSD1 was expressed in fibroblasts from all tissues but mRNA levels and enzyme activity were higher in synovial fibroblasts (2-fold and 13-fold higher mRNA levels in dermal and synovial fibroblasts, respectively, relative to bone marrow). Expression and activity of the enzyme increased in all fibroblasts following treatment with tumour necrosis factor-α or IL-1β (bone marrow: 8-fold and 37-fold, respectively, compared to vehicle; dermal fibroblasts: 4-fold and 14-fold; synovial fibroblasts: 7-fold and 31-fold; all P < 0.01 compared with vehicle). Treatment with IL-4 or interferon-γ was without effect, and there was no difference in 11β-HSD1 expression between fibroblasts (from any site) obtained from patients with rheumatoid arthritis or osteoarthritis. In the presence of 100 nmol/l cortisone, IL-6 production – a characteristic feature of synovial derived fibroblasts – was significantly reduced in synovial but not dermal or bone marrow fibroblasts. This was prevented by co-treatment with an 11β-HSD inhibitor, emphasizing the potential for autocrine activation of glucocorticoids in synovial fibroblasts. These data indicate that differences in fibroblast-derived glucocorticoid production (via the enzyme 11β-HSD1) between cells from distinct anatomical locations may play a key role in the predeliction of certain tissues to develop persistent inflammation.

Role of the Growth Hormone/Insulin-like Growth Factor-1 Paracrine Axis in Rheumatic Diseases

OBJECTIVES

Hypothalamic-pituitary axis abnormalities have been associated with systemic disturbances in several rheumatic diseases. Longitudinal analysis of erythrocyte, serum, urinary and synovial fluid growth hormone (GH), insulin-like growth factor-1 (IGF-1), and somatostatin levels could provide important surrogate measures of disease activity in rheumatic diseases.

METHODS

The authors reviewed the population and longitudinal studies literature on GH, IGF-1, and somatostatin levels in rheumatic disorders using the PubMed and Medlines databases from the National Library of Medicine. In addition to the literature search, primary data were analyzed for basal somatostatin levels in patients with hand, knee, and spine osteoarthritis (OA) as well as primary and secondary hip OA.

RESULTS

A review of the literature supports the view that hypothalamic-pituitary axis dysfunction accompanies clinical symptoms in many rheumatic diseases. In studies from our laboratory, serum GH levels were elevated in patients with OA, rheumatoid arthritis (RA), fibromyalgia, and diffuse idiopathic skeletal hyperostosis but not in patients with gout, pseudogout, or systemic lupus erythematosus. In OA and RA, synovial fluid GH levels exceeded serum GH levels. However, the literature remains controversial regarding the significance of changes in IGF-1 levels in rheumatic disorders. Many studies support an inverse relationship between age and IGF-1. Elevated serum GH levels in various rheumatic diseases were not coupled to changes in serum IGF-1 in diffuse idiopathic skeletal hyperostosis, RA, and fibromyalgia. In particular, serum IGF-1 levels in OA were shown to be lower or no different compared with age-matched normal subjects. Further, in OA, impaired articular chondrocyte response to IGF-1 was attributed, in part, to low synovial fluid IGF-1 that further compromised IGF-1 chondrocyte responses as a result of increased levels of synovial fluid IGF-1 binding proteins. Of note, serum somatostatin levels and "specific" somatostatin receptor levels were often lower in RA and systemic lupus erythematosus, but basal serum somatostatin levels were generally not altered in OA.

CONCLUSIONS

The results of these analyses support the view that some rheumatic diseases such as OA and diffuse idiopathic skeletal hyperostosis, heretofore considered to be purely focal and degenerative, could be reclassified as systemic metabolic disturbances. We propose that serum GH, IGF-1, and somatostatin levels be monitored on a longitudinal basis during the course of medical therapy of rheumatic diseases to determine the extent to which changes in clinical symptoms (exemplified by reduced pain and inflammation and improved range of joint motion) are accompanied by changes in the basal concentration of these hypothalamic/pituitary-related hormones.

Brain-immune interactions and disease susceptibility

Many studies have established the routes by which the immune and central nervous (CNS) systems communicate. This network of connections permits the CNS to regulate the immune system through both neuroendocrine and neuronal pathways. In turn, the immune system signals the CNS through neuronal and humoral routes, via immune mediators and cytokines. This regulatory system between the immune system and CNS plays an important role in susceptibility and resistance to autoimmune, inflammatory, infectious and allergic diseases. This review focuses on the regulation of the immune system via the neuroendocrine system, and underlines the link between neuroendocrine dysregulation and development of major depressive disorders, autoimmune diseases and osteoporosis.

Rheumatoid Arthritis: Neuroendocrine Immune Integrated Physiopathogenetic Perspectives and Therapy

Current concepts of neuroendocrine immune (NEI) aspects of rheumatoid arthritis (RA) are reviewed and recent clinical trials of glucocorticoids and sex steroids are summarized. A novel physiopathogenetic perspective is presented. Data are provided of amplified NEI interactions and dysregulation, many years before symptomatic onset of RA. Chronic imbalances between the NEI, vascular endothelial, neural, and other vital counterregulatory intertwined networks are proposed to cause RA and influence its disease activity. Future research may reveal means of diminishing the onset risk as well as disease activity of RA by controlling these imbalances of NEI and other vital networks.

DREAMing about arthritic pain

The experience of acute pain serves a crucial biological purpose: it alerts a living organism to environmental dangers, inducing behavioural responses which protect the organism from further damage. In contrast, chronic pain arising from disease states and/or pathological functioning of the nervous system offers no advantage and may be debilitating to those afflicted. Despite recent advances in our understanding of pain mechanisms, the satisfactory management of pathological pain eludes current treatment strategies. We have demonstrated in a previous study on dream deficient mice the pivotal role of downstream regulatory element antagonistic modulator (DREAM) in modulating pain sensitivity in a number of behavioural models, including acute and chronic neuropathic pain. DREAM is a novel calcium binding transcriptional repressor for the prodynorphin gene in spinal cord neurones. The marked attenuation in pain behaviour exhibited by dream-/- mice was shown, by pharmacological and biochemical analyses, to be due to increased activation of the endogenous kappa-opioid system. Importantly, loss of DREAM also attenuated inflammatory pain. Thus, DREAM and the DREAM pathway constitute a novel therapeutic paradigm for the treatment of chronic pain in arthritis.

Models of adjustment to chronic illness: Using the example of rheumatoid arthritis

There are a number of theoretical frameworks that attempt to explain how individuals may adjust to threats to health and serious physical illness. The three major paradigms that attempt to organize key components of health and adaptation to illness include the following: the biomedical model which emphasizes disease; psychological models of adaptation to illness; and biopsychosocial models with the latter two emphasizing health, functioning, and well-being. Each of these three major paradigms, including biomedical, psychosocial, and biopsychosocial frameworks, is discussed and critiqued in turn, and contributions and theoretical issues in terms of adjustment to chronic illness, particularly rheumatoid arthritis (RA), are highlighted. Furthermore, a biopsychosocial framework for conceptualizing adjustment to physical illness is proposed that incorporates elements from key existing biomedical and psychosocial models of adaptation to chronic physical health issues.

Involvement and role of the hypothalamo-pituitary-adrenal (HPA) stress axis in animal models of chronic pain and inflammation

Hypothalamo-pituitary-adrenal (HPA) axis changes have been reported in several disease states, including major depressive disorder, rheumatoid arthritis, multiple sclerosis and various other conditions associated with chronic pain. These observations suggest that stress and the HPA axis may play important roles in the pathology of these diseases. In order to contribute to a better understanding of the role that chronic stress may play in human pathology, this review article explores the involvement of the HPA axis in those animal models of chronic pain and inflammation that entail persistent rather than intermittent stress.

Nonpeptide corticotropin-releasing hormone receptor type 1 antagonists and their applications in psychosomatic disorders

Overproduction of corticotropin-releasing hormone (CRH) and stress system abnormalities are seen in psychiatric diseases such as depression, anxiety, eating disorders, and addiction. Investigations of CRH type 1 receptor (CRHR1) nonpeptide antagonists suggest therapeutic potential for treatment of these and other neuropsychiatric diseases. However, overproduction of CRH in the brain and on its periphery and disruption of the hypothalamic-pituitary-adrenal axis are also found in 'somatic' disorders. Some rare forms of Cushing's disease and related pituitary/adrenal disorders are obvious applications for CRHR1 antagonists. In addition, however, these antagonists may also be effective in treating more common somatic diseases. Patients with obesity and metabolic syndrome who often have subtle, but chronic hypothalamic-pituitary-adrenal hyperactivity, which may reflect central dysregulation of CRH and consequently glucocorticoid hypersecretion, could possibly be treated by administration of CRHR1 antagonists. Hormonal, autonomic, and immune aberrations are also present in chronic inflammatory, autoimmune, and allergic diseases, with considerable evidence linking CRH with the observed abnormalities. Furthermore, autonomic dysregulation is a prominent feature of common gastrointestinal disorders, such as irritable bowel syndrome and peptic ulcer disease. Patients with irritable bowel syndrome and other gastrointestinal disorders frequently develop altered pain perception and affective symptoms. CRH acts peripherally to modulate bowel activity both directly through the autonomic system and centrally by processing viscerosensory and visceromotor neural signals. This review presents clinical and preclinical evidence for the role of CRH in the pathophysiology of these disorders and for potential diagnostic and therapeutic applications of CRHR1 antagonists. Recognition of a dysfunctional stress system in these and other diseases will alter the understanding and treatment of 'psychosomatic' disorders.

Leptin consumption in the inflamed joints of patients with rheumatoid arthritis

BACKGROUND

Leptin has been shown to participate in bone remodelling and leptin substitution reported to have a protective effect in experimental septic arthritis.

OBJECTIVE

To assess leptin levels in inflamed joints and plasma of patients with RA.

MATERIAL AND METHODS

Leptin concentrations were assessed in matched blood and synovial fluid samples from 76 patients with RA. Blood samples from 34 healthy subjects acted as additional controls. Results were analysed and correlated with duration and activity of RA, x ray changes, and treatment at time of sampling.

RESULTS

In patients with RA, leptin levels were significantly higher in plasma than in synovial fluid samples obtained simultaneously and higher than in control samples. Plasma and synovial fluid leptin levels correlated strongly. Locally in the joint, leptin levels were related to WBC count. Such a relation was not seen in the bloodstream. Leptin levels were not related to sex, age, or disease duration. Difference between leptin levels in plasma and synovial fluid was greater in non-erosive arthritis (5.1 (SEM 1.2) v 3.7 (0.9) ng/ml, p=0.006), than in patients with erosive joint disease (6.2 (1.0) v 5.4 (0.8) ng/ml, NS). Methotrexate treatment was associated with relatively high plasma leptin levels, while treatment with other DMARDs was associated with lower leptin levels than in patients receiving no DMARD treatment (p=0.0005).

CONCLUSIONS

Leptin production was significantly increased in patients with RA compared with healthy controls. Synovial fluid leptin levels were significantly lower than in matched plasma samples, suggesting an in situ consumption of this molecule.

Neural immune pathways and their connection to inflammatory diseases

Inflammation and inflammatory responses are modulated by a bidirectional communication between the neuroendocrine and immune system. Many lines of research have established the numerous routes by which the immune system and the central nervous system (CNS) communicate. The CNS signals the immune system through hormonal pathways, including the hypothalamic-pituitary-adrenal axis and the hormones of the neuroendocrine stress response, and through neuronal pathways, including the autonomic nervous system. The hypothalamic-pituitary-gonadal axis and sex hormones also have an important immunoregulatory role. The immune system signals the CNS through immune mediators and cytokines that can cross the blood-brain barrier, or signal indirectly through the vagus nerve or second messengers. Neuroendocrine regulation of immune function is essential for survival during stress or infection and to modulate immune responses in inflammatory disease. This review discusses neuroimmune interactions and evidence for the role of such neural immune regulation of inflammation, rather than a discussion of the individual inflammatory mediators, in rheumatoid arthritis.

Neuroimmunoendocrinology of the rheumatic diseases: past, present, and future

Adaptation to stressful stimuli, maintenance of homeostasis, and ultimately, survival require bidirectional feedback communication among components of the stress response and immune and endocrine systems. Substantial progress has been made in delineating molecular, cellular, and systemic physiologic mechanisms underlying this communication, particularly mechanisms that target the immune system. For example, our understanding of the immunomodulatory activities of numerous neuroendocrine mediators, such as cortisol, estrogen, testosterone, DHEA, catecholamines, corticotropin-releasing hormone, and adenosine, has advanced substantially. Substantial progress has also been made in defining how abnormalities involving these factors may contribute to the initiation, progression, and severity of autoimmune rheumatic diseases, particularly rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). For RA, the available data support the view that inflammatory and immune system inhibitory mechanisms, involving the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system are deficient. Age, gender, and reproductive status acting, in part, through gonadal hormonal effects on disease susceptibility genes also appear likely to modulate the inhibitory stress response systems and immune function. Animal model data also have provided direct evidence that many autoimmune disease regulatory genes are gender influenced. For SLE, a growing body of recent data indicates that estrogens and androgens exert contrasting effects on B-lymphocytes (i.e., estrogens enhance and testosterone suppresses autoantibody production). These observations provide potential new insights into SLE pathogenesis and gender differences in prevalence. Continued investigation will refine our understanding of these observations and will uncover even more extensive interactions of the nervous, immune, and endocrine systems. Moreover, it is highly likely that improved understanding of these interactions will translate into improved therapy for the rheumatic diseases.