Evolutionary medicine and chronic inflammatory state—known and new concepts in pathophysiology

During the last 10 years, a series of exciting observations has led to a new theory of pathophysiology using insights from evolutionary biology and neuroendocrine immunology to understand the sequelae of chronic inflammatory disease. According to this theory, disease sequelae can be explained based on redirection of energy-rich fuels from storage organs to the activated immune system. These disease sequelae are highly diverse and include the following: sickness behavior, anorexia, malnutrition, muscle wasting–cachexia, cachectic obesity, insulin resistance with hyperinsulinemia, dyslipidemia, increase of adipose tissue near inflamed tissue, alterations of steroid hormone axes, elevated sympathetic tone and local sympathetic nerve fiber loss, decreased parasympathetic tone, hypertension, inflammation-related anemia, and osteopenia. Since these disease sequelae can be found in many animal models of chronic inflammatory diseases with mammals (e.g., monkeys, mice, rats, rabbits, etc.), the evolutionary time line goes back at least 70 million years. While the initial version of this theory could explain prominent sequelae of chronic inflammatory disease, it did not however address two features important in the pathogenesis of immune-mediated diseases: the time point when an acute inflammatory disease becomes chronic, and the appearance of hypertension in chronic inflammation. To address these aspects more specifically, a new version of the theory has been developed. This version defines more precisely the moment of transition from acute inflammatory disease to chronic inflammatory disease as a time in which energy stores become empty (complete energy consumption). Depending on the amount of stored energy, this time point can be calculated to be 19–43 days. Second, the revised theory addresses the mechanisms of essential hypertension since, on the basis of water loss, acute inflammatory diseases can stimulate water retention using a positively selected water retention system (identical to the energy provision system). In chronic smoldering inflammation, however, there is no increased water loss. In contrast, there is increased water generation in inflamed tissue and inflammatory cells, and the activation of the water retention system persists. This combination leads to a net increase of the systemic fluid volume, which is hypothesized to be the basis of essential hypertension (prevalence in adults 22–32%)

Stress of different types increases the proinflammatory load in rheumatoid arthritis

Stress in patients with chronic inflammatory diseases such as rheumatoid arthritis (RA) stimulates proinflammatory mechanisms due to the defect of stress response systems (for example, the sympathetic nervous system and the hypothalamic–pituitary–adrenal axis). Among other mechanisms, the loss of sympathetic nerve fibers in inflamed tissue and inadequate cortisol secretion in relation to inflammation lead to an enhanced proinflammatory load in RA. Stress and the subsequent stimulation of inflammation (systemic and local) lead to increased sensitization of pain and further defects of stress response systems (vicious cycle of stress, pain, and inflammation)

Impact of the Sensory and Sympathetic Nervous System on Fracture Healing in Ovariectomized Mice

The peripheral nervous system modulates bone repair under physiological and pathophysiological conditions. Previously, we reported an essential role for sensory neuropeptide substance P (SP) and sympathetic nerve fibers (SNF) for proper fracture healing and bone structure in a murine tibial fracture model. A similar distortion of bone microarchitecture has been described for mice lacking the sensory neuropeptide alpha-calcitonin gene-related peptide (alpha-CGRP). Here, we hypothesize that loss of SP, alpha-CGRP, and SNF modulates inflammatory and pain-related processes and also affects bone regeneration during fracture healing under postmenopausal conditions. Intramedullary fixed femoral fractures were set to 28 days after bilateral ovariectomy (OVX) in female wild type (WT), SP-, alpha-CGRP-deficient, and sympathectomized (SYX) mice. Locomotion, paw withdrawal threshold, fracture callus maturation and numbers of TRAP-, CD4-, CD8-, F4/80-, iNos-, and Arg1-positive cells within the callus were analyzed. Nightly locomotion was reduced in unfractured SP-deficient and SYX mice after fracture. Resistance to pressure was increased for the fractured leg in SP-deficient mice during the later stages of fracture healing, but was decreased in alpha-CGRP-deficient mice. Hypertrophic cartilage area was increased nine days after fracture in SP-deficient mice. Bony callus maturation was delayed in SYX mice during the later healing stages. In addition, the number of CD 4-positive cells was reduced after five days and the number of CD 8-positive cells was additionally reduced after 21 days in SYX mice. The number of Arg1-positive M2 macrophages was higher in alpha-CGRP-deficient mice five days after fracture. The alkaline phosphatase level was increased in SYX mice 16 days after fracture. Absence of alpha-CGRP appears to promote M2 macrophage polarization and reduces the pain threshold, but has no effect on callus tissue maturation. Absence of SP reduces locomotion, increases the pain-threshold, and accelerates hypertrophic callus tissue remodeling. Destruction of SNF reduces locomotion after fracture and influences bony callus tissue remodeling during the later stages of fracture repair, whereas pain-related processes are not affected

11β-Hydroxysteroid Dehydrogenase Enzymes Modulate Effects of Glucocorticoids in Rheumatoid Arthritis Synovial Cells

The tissue availability of active glucocorticoids (cortisol in humans) depends on their rate of synthesis from cholesterol, downstream metabolism, excretion and interconversion. The latter is mediated by the 11β-hydroxysteroid dehydrogenases (11βHSDs). In this review, we summarize the features of the two isoenzymes, 11βHSD1 and 11βHSD2, and current available experimental data related to 11βHSDs, which are relevant in the context of synovial cells in rheumatoid arthritis (RA). We conclude that due to complex feedback mechanisms inherent to the hypothalamic-pituitary-adrenal axis, currently available transgenic animal models cannot display the full potential otherwise inherent to the techniques. Studies with tissue explants, mixed synovial cell preparations, cell lines derived from synovial cells, and related primary cells or established cell lines indicate that there are relatively clear differences between the two isoenzymes. 11βHSD1 is expressed primarily in fibroblasts and osteoblasts, and may be responsible for fibroblast survival and aid in the resolution of inflammation, but it is also involved in bone damage. 11βHSD2 is expressed primarily in macrophages and lymphocytes, and may be responsible for their survival, suggesting that it is critical in chronic inflammation. The situation in synovial tissue would allow 11βHSD2-expressing cells to tap the energy resources of 11βHSD1-expressing cells. The overall properties of this local glucocorticoid interconversion system might limit therapeutic use of glucocorticoids in RA

The sympathetic nervous system stimulates anti-inflammatory B cells in collagen-type II-induced arthritis

Background: As previously shown, the sympathetic nervous system (SNS) shows proinflammatory activity during initiation of arthritis but is anti-inflammatory in established collagen-induced arthritis (CIA). Interleukin 10 (IL-10)-producing B cells suppress arthritis and are a potential target of the SNS because (1) B cells express functional β2-adrenoceptors (β2ARs) and (2) IL-10, at least in monocytes/macrophages, is regulated in a cAMP/PKA/CREB-dependent manner. Objective: To test the hypothesis that anti-inflammatory effects of the SNS in CIA are mediated by stimulating IL-10-producing anti-inflammatory B cells. Methods: Collagen-induced arthritis in DBA/1 mice, sympathectomy, adoptive B cell transfer, in vitro B cell culture, and assessment of B cell IL-10 production. Results and conclusion: Mice treated with B cells from SNS-intact mice showed less severe arthritis than mice treated with B cells from sympathectomised mice. This anti-inflammatory action of B cells from SNS-intact mice correlated with increased IL-10 produced by B cells, which was mediated by norepinephrine (NE), in a β2AR, PKA-dependent manner. However, an NE-mediated increase in IL-10 was seen only in B cells from immunised but not naive mice, explaining in part the anti-inflammatory properties of the SNS in the late phase of arthritis. Finally, animals treated with B cells isolated from immunised mice and activated in vitro in the presence of a β2AR stimulus showed a decrease in arthritis severity in comparison with controls, an approach that might be used for future cellular treatment strategies

Inadequate corticosterone levels relative to arthritic inflammation are accompanied by altered mitochondria/cholesterol breakdown in adrenal cortex: a steroid-inhibiting role of IL-1β in rats

Objectives In rheumatoid arthritis, inadequate cortisol secretion was observed relative to inflammation, but reasons are unknown. Human adrenal glands cannot be investigated due to ethical reasons. Thus, a model of arthritis was studied to test inadequate glucocorticoid secretion and adrenocortical alterations. Methods Arthritis in DA rats was induced by collagen type II. Plasma hormone (cytokine) levels were determined by ELISA or radioimmunoassay (Luminex). Adrenocortical cells were investigated making use of in vitro culture, immunohistochemistry and imaging techniques, cholesterol uptake studies and electron microscopical morphological analyses of adrenocortical lipid droplets and mitochondria. Results During the course of arthritis, corticosterone and adrenocorticotropic hormone (ACTH) levels were only elevated on day 1 after immunisation but were in the normal range from day 5 to 55. Serum levels of corticosterone relative to IL-1β were markedly lower in arthritis than in controls. IL-1β inhibited ACTH-stimulated corticosterone secretion from adrenocortical cells in vitro. Cholesterol uptake receptor SR-BI protein was unchanged. Number of altered swollen and cavitated mitochondria increased during the course of arthritis (maximum on day 55), and this was correlated to reduced breakdown of lipid droplets and increased Sudan III-positive lipid accumulation from day 28 to 55. Reduced lipid breakdown measured as a high number of homogenous lipid droplets negatively correlated with plasma corticosterone (p=0.022). Adrenocortical tissue density of normal mitochondria positively correlated with serum corticosterone levels. Conclusions This study on inadequate adrenal glucocorticoid secretion in arthritis demonstrated altered mitochondria and altered lipid breakdown paralleled by low corticosterone levels in relation to inflammation. IL-1β is a key cytokine