Neurohumoral mechanisms in rheumatoid arthritis

Structural and functional interactions between six-transmembrane μ-opioid receptors and β2-adrenoreceptors modulate opioid signaling

The primary molecular target for clinically used opioids is the μ-opioid receptor (MOR). Besides the major seven-transmembrane (7TM) receptors, the MOR gene codes for alternatively spliced six-transmembrane (6TM) isoforms, the biological and clinical significance of which remains unclear. Here, we show that the otherwise exclusively intracellular localized 6TM-MOR translocates to the plasma membrane upon coexpression with β₂-adrenergic receptors (β₂-ARs) through an interaction with the fifth and sixth helices of β₂-AR. Coexpression of the two receptors in BE(2)-C neuroblastoma cells potentiates calcium responses to a 6TM-MOR ligand, and this calcium response is completely blocked by a selective β₂-antagonist in BE(2)-C cells, and in trigeminal and dorsal root ganglia. Co-administration of 6TM-MOR and β₂-AR ligands leads to substantial analgesic synergy and completely reverses opioid-induced hyperalgesia in rodent behavioral models. Together, our results provide evidence that the heterodimerization of 6TM-MOR with β₂-AR underlies a molecular mechanism for 6TM cellular signaling, presenting a unique functional responses to opioids. This signaling pathway may contribute to the hyperalgesic effects of opioids that can be efficiently blocked by β₂-AR antagonists, providing a new avenue for opioid therapy.

Asymmetric scleroderma in a CVA patient

We describe a systemic sclerosis and cerebral vascular accident case in which the cutaneous manifestation and the distal acroosteolysis occurred in an asymmetrical way in the non-paretic limb. The subsequent sclerodermic alterations and the acroosteolysis acquired an asymmetric pattern, sparing the patient's hemiparetic side. Although a number of definitions of this protective effect may be found in other rheumatic diseases, such as rheumatoid arthritis and gout, we found in the literature only one previous case describing the protective effect of the hemiplegia in scleroderma.

Failure of catecholamines to shift T-cell cytokine responses toward a Th2 profile in patients with rheumatoid arthritis

To further understand the role of neuro-immunological interactions in the pathogenesis of rheumatoid arthritis (RA), we studied the influence of sympathetic neurotransmitters on cytokine production of T cells in patients with RA. T cells were isolated from peripheral blood of RA patients or healthy donors (HDs), and stimulated via CD3 and CD28. Co-incubation was carried out with epinephrine or norepinephrine in concentrations ranging from 10(-5) M to 10(-11) M. Interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha, interleukin (IL)-4, and IL-10 were determined in the culture supernatant with enzyme-linked immunosorbent assay. In addition, IFN-gamma and IL-10 were evaluated with intracellular cytokine staining. Furthermore, basal and agonist-induced cAMP levels and catecholamine-induced apoptosis of T cells were measured. Catecholamines inhibited the synthesis of IFN-gamma, TNF-alpha, and IL-10 at a concentration of 10(-5) M. In addition, IFN-gamma release was suppressed by 10(-7) M epinephrine. Lower catecholamine concentrations exerted no significant effect. A reduced IL-4 production upon co-incubation with 10(-5) M epinephrine was observed in RA patients only. The inhibitory effect of catecholamines on IFN-gamma production was lower in RA patients as compared with HDs. In RA patients, a catecholamine-induced shift toward a Th2 (type 2) polarised cytokine profile was abrogated. Evaluation of intracellular cytokines revealed that CD8-positive T cells were accountable for the impaired catecholaminergic control of IFN-gamma production. The highly significant negative correlation between age and catecholamine effects in HDs was not found in RA patients. Basal and stimulated cAMP levels in T-cell subsets and catecholamine-induced apoptosis did not differ between RA patients and HDs. RA patients demonstrate an impaired inhibitory effect of catecholamines on IFN-gamma production together with a failure to induce a shift of T-cell cytokine responses toward a Th2-like profile. Such an unfavorable situation is a perpetuating factor for 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.

Inflammation in juvenile idiopathic arthritis

Inflammation evolved to aid in the clearance of microorganisms. In pediatric arthritides, the inflammation persists and causes damage to the joint. The contribution of the innate immune system to inflammation is significant and can be exploited therapeutically. Although cells of the adaptive immune system such as T cells and B cells participate in the disease process, many of the features of arthritis are directly attributable to inflammatory mediators. Recent advances in the understanding of these processes have led to dramatic improvements in treatment.

Neuroendocrine immune mechanisms in rheumatic diseases. An overview and future implications

A new physiopathogenetic paradigm may be proposed for RA and possibly its related systemic rheumatic diseases (i.e., mechanisms whereby multiple risk factors initially perturb the homeostasis of core physiologic components over an extended premorbid phase, which may progress to clinical disease in later decompensated stages). These complex interactive processes are likely to be individualized according to genetic, nongenomic somatic, developmental, behavioral, and environmental influences. Future research promises to further elucidate the roles of neuroendocrine mechanisms in the rheumatic diseases and offers promise for enhanced therapies and possible avenues for disease modification if not eventual prevention.

Interactions of autonomic nervous, neuroendocrine, and immune systems in rheumatoid arthritis

In general, it is assumed that the two pathways (i.e., HPA axis and sympathetic nervous system) probably act cooperatively to maintain homeostasis. The previously mentioned studies clearly point to a disturbance in the interaction between the ANS, the HPA axis, and the immune system in chronic rheumatic diseases (Fig. 2). Even early on in the course of RA, these changes can be observed. Along with the results obtained in animal models, an important role of neuroendocrine interactions in the pathogenesis of RA is proposed. Further studies are required to establish the exact contribution of the ANS in the initiation and perpetuation of RA. To date, it is quite obvious that neuropeptides play a part in the orchestration of the various molecules (e.g., cytokines) exerting modulatory effects on immune cells. One can speculate that therapeutic implications are likely to result from investigations on the ANS-immune interactions. Based on early observations that blocking catecholamine actions ameliorate symptoms of RA, it is quite promising to follow this avenue in investigating ANS-immune interactions of various time points of the disease. Conversely, further studies are required to determine the contribution of the HPA axis to the onset of RA. Results from ongoing studies are eagerly awaited so as to establish new therapeutic options. In the future,it may be possible to interfere with the inflammatory process in RA by an exactly timed neuroendocrine intervention right at or even before the onset of disease. Therapy with steroids in RA might be better planned based on the genetically determined reactivity of an individual's HPA axis. In this respect, a recent report by Masi et al is of special interest. Based on the current literature on the disturbances in the neuroendocrine, immune, and microvascular systems found in early RA, the authors hypothesize that an imbalance in the interactive homeostasis of these systems develops during a long preclinical phase and eventually leads to the outbreak of the disease in genetically predisposed individuals. This interesting hypothesis includes the perspective that individuals prone to develop RA may be identified in a preclinical phase and treated prophylactically. In any event, results from all these studies are promising in two ways: to gain more insight in the pathogenic process of RA and to establish novel therapies to help the patients bear their burden of a chronic rheumatic disease.

Disease activity related catecholamine response of lymphocytes from patients with rheumatoid arthritis

In patients with chronic rheumatic diseases, a decreased density of beta 2-adrenergic receptors (beta 2R) on peripheral blood mononuclear cells (PBMC) could be demonstrated negatively correlating with various disease activity parameters. The aim of the present study was to determine the impact of this decrease on catecholamine response of PBMC from patients with rheumatoid arthritis (RA) in vitro. PBMC from 17 patients with RA and 6 healthy blood donors (HD) were investigated. The effects of epinephrine (E) and norepinephrine (NE) on PBMC proliferation were studied using cells activated with phytohemagglutinin (PHA) and monoclonal anti-CD3-antibodies (OKT3), respectively. The results revealed that lymphocytes of patients with RA showed a significantly reduced influence of catecholamines on PBMC function. In RA patients with high disease activity only, a shift to alpha 1-adrenergic-mediated catecholamine effects upon PBMC reactivity could be observed. The study demonstrates the intricate relationship between PBMC reactivity and catecholamine effects that is mediated via alpha- and beta-adrenergic receptors due to disease activity. In this respect the altered catecholamine response of PBMC from patients with RA may contribute to the pathogenic process of RA.

Reduced catecholamine response of lymphocytes from patients with rheumatoid arthritis

Catecholamines modulate lymphocyte function via stimulation of beta2-adrenergic receptors (beta2R). Previous investigations revealed a decreased density of beta2R on peripheral blood mononuclear cells (PBMC) in patients with chronic rheumatic diseases. Aim of the present study was to determine the impact of this decrease on catecholamine response of PBMC from patients with rheumatoid arthritis (RA) in vitro. PBMC from 17 patients with RA and 12 healthy blood donors (HD) were investigated. Beta2R were determined by a radioligand binding assay. The effects of epinephrine (E) and norepinephrine (NE) on PBMC proliferation were studied using cells activated with pokeweed mitogen (PWM) and monoclonal anti-CD3-antibodies (OKT3), respectively. In parallel, alpha1- or beta-receptor antagonist were added to the culture to determine the specificity of the catecholaminergic effects. The results showed that depending on the stimulus and the catecholamine concentration employed E and NE exert inhibitory (OKT3) or stimulatory signals (PWM) on lymphocyte proliferation. Inhibitory effects could be abolished by adding beta-antagonist, while stimulatory signals were diminished after addition of alpha1- of beta-antagonist. Patients with RA showed a significantly reduced density of beta2R compared to HD paralleled by a significantly reduced influence of catecholamines on lymphocyte function. The study demonstrates the intricate relationship between PBMC reactivity and catecholamine effects that are mediated via alpha1- and beta-adrenergic receptors. In this respect the reduced catecholamine response of PBMC from RA patients may contribute to the pathogenic process of RA.

Activation of CNS circuits producing a neurogenic cystitis: evidence for centrally induced peripheral inflammation

We present a model of neurogenic cystitis induced by viral infection of specific neuronal circuits of the rat CNS. Retrograde infection by pseudorabies virus (PRV) of neuronal populations neighboring those that innervate the bladder consistently led to a localized immune response in the CNS and bladder inflammation. Infection of bladder circuits themselves or of circuits distant from these rarely produced cystitis. Absence of virus in bladder and urine ruled out an infectious cystitis. Total denervation of the bladder, selective C-fiber deafferentation, or bladder sympathectomy prevented cystitis without affecting the CNS disease, indicating a neurogenic component to the inflammation. The integrity of central bladder-related circuits is necessary for the appearance of bladder inflammation, because only CNS lesions affecting bladder circuits, i.e., bilateral dorsolateral or ventrolateral funiculectomy, as well as bilateral lesions of Barrington's nucleus/locus coeruleus area, prevented bladder inflammation. The close proximity in the CNS of noninfected visceral circuits to infected somatic neurons would thus permit a bystander effect, leading to activation of the sensory and autonomic circuits innervating the bladder and resulting in a neurogenic inflammation localized to the bladder. The present study indicates that CNS dysfunction can bring about a peripheral inflammation.