IL-32, a proinflammatory cytokine in rheumatoid arthritis

Neutral sphingomyelinase inhibition participates to the benefits of N-acetylcysteine treatment in post-myocardial infarction failing heart rats

Deficiency in cellular thiol tripeptide glutathione (L-gamma glutamyl-cysteinyl-glycine) determines the severity of several chronic and inflammatory human diseases that may be relieved by oral treatment with the glutathione precursor N-acetylcysteine (NAC). Here, we showed that the left ventricle (LV) of human failing heart was depleted in total glutathione by 54%. Similarly, 2-month post-myocardial infarction (MI) rats, with established chronic heart failure (CHF), displayed deficiency in LV glutathione. One-month oral NAC treatment normalized LV glutathione, improved LV contractile function and lessened adverse LV remodelling in 3-month post-MI rats. Biochemical studies at two time-points of NAC treatment, 3 days and 1 month, showed that inhibition of the neutral sphingomyelinase (N-SMase), Bcl-2 depletion and caspase-3 activation, were key, early and lasting events associated with glutathione repletion. Attenuation of oxidative stress, downregulation of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) and its TNF-R1 receptor were significant after 1-month NAC treatment. These data indicate that, besides glutathione deficiency, N-SMase activation is associated with post-MI CHF progression, and that blockade of N-SMase activation participates to post-infarction failing heart recovery achieved by NAC treatment. NAC treatment in post-MI rats is a way to disrupt the vicious sTNF-alpha/TNF-R1/N-SMase cycle.

Cytokines in the pathogenesis of rheumatoid arthritis

Cytokines regulate a broad range of inflammatory processes that are implicated in the pathogenesis of rheumatoid arthritis. In rheumatoid joints, it is well known that an imbalance between pro- and anti-inflammatory cytokine activities favours the induction of autoimmunity, chronic inflammation and thereby joint damage. However, it remains less clear how cytokines are organized within a hierarchical regulatory network, and therefore which cytokines may be the best targets for clinical intervention a priori. Here, we discuss the crucial effector function of cytokines in the immunological processes that are central to the pathogenesis of rheumatoid arthritis.

Epithelial overexpression of interleukin-32alpha in inflammatory bowel disease

Interleukin (IL)-32 is a recently described proinflammatory cytokine, characterized by induction of nuclear factor (NF)-kappaB activation. We studied IL-32alpha expression in the inflamed mucosa of inflammatory bowel disease (IBD). We also investigated mechanisms regulating IL-32alpha expression. Tissue samples were obtained endoscopically or surgically from patients with ulcerative colitis (UC) (n = 10), Crohn's disease (CD) (n = 10), ischaemic colitis (n = 4) and normal colorectal tissues (n = 10). IL-32alpha expression was evaluated by standard immunohistochemical procedure. IL-32 mRNA expression was analysed by Northern blot. IL-32alpha was expressed weakly by colonic epithelial cells from normal individuals and subjects with ischaemic colitis. In the inflamed mucosa of IBD patients, epithelial IL-32alpha expression was increased markedly. In UC and CD patients, IL-32alpha expression was enhanced in affected mucosa compared to non-affected mucosa. In intestinal epithelial cell lines, expression of IL-32alpha mRNA and protein was enhanced by IL-1beta, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha. A combination of TNF-alpha plus IFN-gamma exerted synergistic effects. IL-32alpha induction by IL-1beta and/or TNF-alpha was mediated by NF-kappaB activation. Epithelial IL-32alpha expression was increased in IBD patients, and in CD patients in particular. IL-32alpha might be involved in the pathophysiology of IBD as a proinflammatory cytokine and a mediator of innate immune response.

Emerging cytokine targets in rheumatoid arthritis

PURPOSE OF REVIEW

The utility of cytokines as therapeutic targets in rheumatoid arthritis has been unequivocally demonstrated by the success of tumour necrosis factor blockade in clinical practice. Partial and non-responses to tumour necrosis factor blocking agents, however, together with the increasing clinical drive to remission induction, requires that further therapeutic targets be identified.

RECENT FINDINGS

Numerous cytokine activities with pathogenetic potential have now been demonstrated in rheumatoid arthritis synovial membrane, including members of the IL-1 superfamily and the IL-12 superfamily. Continued efforts are ongoing to target IL-6 and IL-15 in clinical trials with promising data emerging. There is particular interest in the biology of IL-17 and of the recently described IL-32 as critical effector mediators.

SUMMARY

Novel cytokine activities are emerging on an ongoing basis. There remain difficulties in ascribing the optimal regulatory hierarchy for given moieties on the basis of existing preclinical model systems. This in turn poses novel challenges in determining which cytokines represent the best therapeutic targets.

Update on cytokines in rheumatoid arthritis

PURPOSE OF REVIEW

There have recently been fewer publications describing novel cytokines in rheumatoid arthritis. In the present review we focus on cytokines not previously implicated in contributing to the pathogenesis of rheumatoid arthritis.

RECENT FINDINGS

The detection of IL-17 and factors that drive the differentiation and expansion of ThIL-17 cells, particularly in mouse models, clearly place IL-17 as a potential therapeutic target in rheumatoid arthritis. The emergence of other novel cytokines, notably IL-20 and IL-22, is of interest, not least by displaying proinflammatory effects particularly on fibroblasts - in contrast to their family member IL-10, the most potent anti-inflammatory cytokine. IL-32 is also of interest, with proinflammatory effects both on myeloid and nonmyeloid cells.

SUMMARY

It is unclear whether the novel cytokines described in the present review will influence clinical practise. The involvement of IL-17 in murine arthritis may not translate as effectively to human arthritis - the ultimate test is a clinical trial in humans. The lack of efficacy of a recent anti-MCP-1/CCL-2 trial in rheumatoid arthritis highlights this dilemma. Finally, while technological advances including microarray analysis have broadened the scope for cytokine detection in rheumatoid arthritis, these methods have yet to translate to therapy in the clinic.

Cellular targets of interleukin-18 in rheumatoid arthritis

Recent data are presented which indicate a critical role for interleukin (IL)-18 in rheumatoid arthritis (RA). The T cells and macrophages invading the synovium or in the synovial fluid are the chief cellular targets of IL-18 in RA. Neutrophils, dendritic cells and endothelial cells may also be cellular mediators of IL-18. The direct effect of IL-18 on fibroblast-like synoviocytes or chondrocytes may not be essential or important. In RA, IL-18, which is mainly produced by macrophages, activates T cells and macrophages to produce proinflammatory cytokines, chemokines, adhesion molecules and RANKL which, in turn, perpetuate chronic inflammation and induce bone and cartilage destruction.

Decreased induction of IL-1β in fibroblast-like synoviocytes: A possible regulatory mechanism maintaining joint homeostasis

The response of fibroblast-like synoviocytes (FLS) to inflammatory stimuli was compared to their, respectively, derived dermal fibroblasts (DF) to determine whether regulatory controls exist within FLS to insure normal joint homeostasis. We further analyzed whether the loss of the normal regulatory controls present within the FLS could predispose to the development of non-rheumatic joint disease (non-RA). Primary fibroblast cell lines were generated from synovial and skin tissue from ten rheumatoid arthritis (RA) and ten non-RA patients. Cell lines were pulse labeled with [(35)S]-methionine and stimulated with TNFalpha or IL-1beta. Protein synthesis of IL-1beta, IL-6 and IL-8 was quantitated following immunoprecipitation. Gene expression was determined by Northern blot analysis. We noted, IL-1beta was minimally detected in FLS under nonstimulated conditions. In response to stimulation with IL-1beta or TNFalpha, production of IL-1beta was found to be 3.5 and 5-fold lower in FLS, respectively, when compared to DF from the same individual. In contrast, the production of IL-6 and IL-8 in FLS upon stimulation was 3-fold and 1.6-fold higher, respectively, than in DF. Furthermore, induced IL-1beta production in FLS, normalized relative to their, respectively, stimulated DF, was 2.5 times higher in non-RA versus RA-derived cells (p=0.032), an effect noted even after several passages of growth. Our data suggest that inductive expression of IL-1beta in FLS is under specific inhibitory control. Increased production of IL-1beta in FLS of susceptible individuals may lead to a higher risk of developing severe joint damage even in the absence of systemic inflammation.

IL-32, a novel cytokine with a possible role in disease

IL-32 is the name given to the NK4 transcript first reported in IL-2 activated T lymphocytes and natural killer cells 13 years ago without known function. The novel cytokine has six isoforms. In an study to isolate a soluble form of the IL-32 receptor from human urine, IL-32alpha bound proteinase-3 with high affinity and was not affected by enzyme inhibition. IL-32alpha/IL-32gamma were expressed as recombinant molecules. The cytokine exhibits properties characteristic of proinflammatory cytokines and also induces the degradation of inhibitory kappaB and phosphorylation of mitogen activated protein p38. Monoclonal antibodies to IL-32 identify its presence in a variety of human tissues from diseases states. Epithelial cells from healthy subjects express low levels of the cytokine, but in disease conditions such as chronic obstructive pulmonary disease, Crohn's disease and psoriasis, the expression increases markedly. IL-32 is a major transcript in gene array studies in epithelial cells stimulated with IFNgamma in vitro. In rheumatoid arthritis, synovial tissues reveals increased content of IL-32, which correlates with severity of disease. A highly significant correlation has been observed between the number of synovial and macrophagic cells positive for IL-32 and the level of erythrocytes sedimentation, IL-1beta, tumour necrosis factor alpha, and IL-18. Thus, IL-32 exhibits many properties of proinflammatory cytokines and associations with disease severity.

Interactions between IL-32 and tumor necrosis factor alpha contribute to the exacerbation of immune-inflammatory diseases

IL-32 is a newly described cytokine in the human found to be an in vitro inducer of tumor necrosis factor alpha (TNFα). We examined the in vivo relationship between IL-32 and TNFα, and the pathologic role of IL-32 in the TNFα-related diseases – arthritis and colitis. We demonstrated by quantitative PCR assay that IL-32 mRNA was expressed in the lymphoid tissues, and in stimulated peripheral T cells, monocytes, and B cells. Activated T cells were important for IL-32 mRNA expression in monocytes and B cells. Interestingly, TNFα reciprocally induced IL-32 mRNA expression in T cells, monocyte-derived dendritic cells, and synovial fibroblasts. Moreover, IL-32 mRNA expression was prominent in the synovial tissues of rheumatoid arthritis patients, especially in synovial-infiltrated lymphocytes by in situ hybridization. To examine the in vivo relationship of IL-32 and TNFα, we prepared an overexpression model mouse of human IL-32β (BM-hIL-32) by bone marrow transplantation. Splenocytes of BM-hIL-32 mice showed increased expression and secretion of TNFα, IL-1β, and IL-6 especially in response to lipopolysaccharide stimulation. Moreover, serum TNFα concentration showed a clear increase in BM-hIL-32 mice. Cell-sorting analysis of splenocytes showed that the expression of TNFα was increased in resting F4/80⁺ macrophages, and the expression of TNFα, IL-1β and IL-6 was increased in lipopolysaccharide-stimulated F4/80⁺ macrophages and CD11c⁺ dendritic cells. In fact, BM-hIL-32 mice showed exacerbation of collagen-antibody-induced arthritis and trinitrobenzen sulfonic acid-induced colitis. In addition, the transfer of hIL-32β-producing CD4⁺ T cells significantly exacerbated collagen-induced arthritis, and a TNFα blockade cancelled the exacerbating effects of hIL-32β. We therefore conclude that IL-32 is closely associated with TNFα, and contributes to the exacerbation of TNFα-related inflammatory arthritis and colitis.

The impact of endogenous triggers on trauma-associated inflammation

PURPOSE OF REVIEW

Inflammation immediately starting after trauma is a consequence of an efficient host defense system that is not only capable of sensing exogenous and pathogen-derived danger signals, but also endogenous, multifunctional alarm signals, which both can initiate an inflammatory response.

RECENT FINDINGS

Even in the absence of infection, Toll-like receptors play an important role in inflammation via recognition of host-derived, endogenous 'damage signals' like heat shock proteins and 'alarmins' such as the nuclear protein high-mobility group box protein 1, which are presented as a result of tissue trauma. In addition to the Toll-like receptors, a number of other receptors are involved in the host inflammatory response, including the new family of nucleotide oligomerization domain-like receptors capable of sensing the presence of danger signals in the cytoplasm. Important links occur between the Toll-like receptors as key inducers of the pro-forms of interleukin-1beta and interleukin-18 and the activation of certain nucleotide oligomerization domain-like receptors, resulting in inflammasome formation--an essential process leading to the secretion of these proinflammatory cytokines.

SUMMARY

In addition to improved insights into the regulation of traumatic inflammation and the etiology of the systemic inflammatory response syndrome, some endogenous immune triggers seem to have the potential to serve as novel biomarkers in predicting post-traumatic complications.

Inhibition of inflammatory response in transgenic fat-1 mice on a calorie-restricted diet

Both n-3 fatty acids (n-3 FA) and calorie-restriction (CR) exert anti-inflammatory effects in animal models of autoimmunity and inflammation. In the present study we investigated the synergistic anti-inflammatory effects of n-3 FA and CR on LPS-mediated inflammatory responses using fat-1 transgenic mice that generate n-3 FA endogenously. Wild-type (WT) and fat-1 mice were maintained on ad libitum (AL) or CR (40% less than AL) diet for 5 mo; splenocytes were cultured in vitro with/without LPS. Our results show: (i) no difference in body weights between WT and fat-1 mice on AL or CR diets, (ii) lower n-6/n-3 FA ratio in splenocytes from fat-1 mice on both AL and CR diets, (iii) significant reduction in NF-kappaB (p65/p50) and AP-1 (c-Fos/c-Jun) DNA-binding activities in splenocytes from fat-1/CR mice following LPS treatment, and (iv) significant reduction in kappaB- and AP-1-responsive IL-6 and TNF-alpha secretion following LPS treatment in splenocytes from fat-1/CR mice. The inhibition of LPS-mediated effects was more pronounced in fat-1/CR mice when compared to fat-1/AL or WT/CR mice. These data show that transgenic expression of fat-1 results in decreased pro-inflammatory n-6 FA, and demonstrate for the first time that splenocytes from fat-1 mice on CR diet exhibit reduced pro-inflammatory response when challenged with LPS. These results suggest that n-3 lipids with moderate CR may confer protection in autoimmune and inflammatory diseases.

IL-32: an emerging player in the immune response network against tuberculosis?

IL-32 has emerged as an important player in innate and adaptive immune responses. Kundu and Basu discuss a new study in PLoS Medicine that explored the role of IL-32 in the context of M. tuberculosis infection.