Interleukin-6 attenuates agonist-mediated calcium mobilization in murine osteoblastic cells

mgrA regulates staphylococcal virulence important for induction and progression of septic arthritis and sepsis

Septic arthritis and sepsis are common and feared complications of staphylococcal infections, and the increasing antibiotic resistance among staphylococci urge the extended research for virulence factors involved in these diseases. Staphylcoccus aureus produces a number of virulence factors controlled by several global regulatory genes including agr and sarA. MgrA is a recently identified global regulator, belonging to the SarA subfamily, which upregulates expression of several virulence factors including capsule and sortase. In addition, MgrA has been shown to regulate antibiotic resistance and decrease bacterial autolysis. In this study we have assessed the role of mgrA gene expression on induction and progression of septic arthritis and sepsis. Mice inoculated with the mgrA mutant displayed significantly less severe arthritis and showed a significantly better weight development, than wild-type inoculated mice. Importantly, all 10 mice inoculated with the mgrA mutant survived as compared to 70% mortality in the wild-type inoculated mice (p=0.003). In addition, the mgrA mutant showed significantly less bacterial persistence in kidneys as compared to the wild-type strain. We conclude that mgrA regulates virulence factors important for establishment and progression of septic arthritis and sepsis.

Role of Interleukin-6 in the Pathogenesis of an Avian Model of Staphylococcus aureus Arthritis

To evaluate the role of interleukin-6 (IL-6) in arthritis induced by Staphylococcus aureus, a chicken model was developed for study. A total of 120 healthy broilers (8 wk old) were randomly divided into 4 groups. Two groups were injected with 0.35 mL of Staph. aureus (7.1x10(9) cfu/mL) into the right hock joints and the other 2 were injected with 0.35 mL of sterile saline into the same joints. One group of each of the 2 treatment groups was fed levofloxacin at a dose of 5 mg/kg of BW on the third day postinoculation for 4 successive days. Chicken blood samples were obtained on d 0, 1, 4, 7, 14, 21, 28, and 35 postinoculation. Chicken IL-6 (chIL-6) activities and concentrations in serum were quantified by B9 bioassay and human IL-6 ELISA, respectively. The results showed that chIL-6 activities and concentrations were reduced (P<0.05) in the serum of infected broilers treated with levofloxacin compared with birds injected only with Staph. aureus. Levofloxacin treatment had no effect on IL-6 activities and concentrations in uninfected broilers. There was a strong correlation (r=0.91) between serum chIL-6 activities by the B9 bioassay and serum IL-6 concentrations determined by the human IL-6 ELISA. We concluded that chIL-6 is involved in the progression of chicken arthritis induced by Staph. aureus, and that it contributes to disease incidence and mortality.

Experimental model of infection with non-toxigenic strains of Corynebacterium diphtheriae and development of septic arthritis

Corynebacterium diphtheriae is a well-known cause of localized respiratory tract infections. However, this micro-organism can also be associated with invasive infections, such as endocarditis, septic arthritis and osteomyelitis. Invasive infections are often caused by non-toxigenic strains. To set up an in vivo experimental model of C. diphtheriae infection, mice were infected intravenously with different doses (ranging from 1×107 to 5×108 bacteria per mouse) of three non-toxigenic strains, namely ISS-4749, ISS-4746 and ISS-3319. Similar mortality rates were observed with the three strains, with an LD50 ranging from 9×107 to 1·2×108. All strains were arthritogenic, although to different extents. ISS-4749 and ISS-4746 infection resulted in a maximum of 60 and 50 %, respectively, of animals with articular lesions, while in the ISS-3319-infected group only 25 % were positive. There were differences in systemic and joint cytokine production in the three experimental groups. ISS-4749- and ISS-4746-infected mice exhibited higher local levels of interleukin (IL)-6 and IL-1β than ISS-3319-infected animals. At systemic levels, ISS-3319 was able to induce early and sustained production of interferon-γ (IFN-γ), but not IL-6. Conversely, infection with the other strains resulted in high IL-6, but not IFN-γ, production. In conclusion, an experimental model of C. diphtheriae infection was set up, with development of septic arthritis. This model could be useful in studies on the pathogenicity and characterization of virulence factors other than toxin production.

Glucuronoxylomannan, the major capsular polysaccharide of Cryptococcus neoformans, inhibits the progression of group B streptococcal arthritis

Glucuronoxylomannan (GXM), the principal constituent of the Cryptococcus neoformans capsule, modulates the inflammatory response of human monocytes in vitro. Here we examine the efficacy of GXM as a novel anti-inflammatory compound for use against experimental septic arthritis. Arthritis was induced in mice by the intravenous injection of 8 x 10(6) CFU of type IV group B streptococcus (GBS). GXM was administered intravenously in different doses (50, 100, or 200 microg/mouse) 1 day before and 1 day after bacterial inoculation. GXM treatment markedly decreased the incidence and severity of articular lesions. Histological findings showed limited periarticular inflammation in the joints of GXM-treated mice, confirming the clinical observations. The amelioration of arthritis was associated with a significant reduction in the local production of interleukin-6 (IL-6), IL-1beta, macrophage inflammatory protein 1alpha (MIP-1alpha), and MIP-2 and an increase in systemic IL-10 levels. Moreover, peritoneal macrophages derived from GXM-treated mice and stimulated in vitro with heat-inactivated GBS showed a similar pattern of cytokine production. The present study provides evidence for the modulation of the inflammatory response by GXM in vivo and suggests a potential therapeutic use for this compound in pathologies involving inflammatory processes.

Role of interleukin-18 in experimental group B streptococcal arthritis

OBJECTIVE

To assess the role of interleukin-18 (IL-18) in the evolution of septic arthritis induced by group B streptococci (GBS) in mice.

METHODS

CD1 mice were inoculated intravenously with 8 x 10(6) colony-forming units (CFU) of type IV GBS (strain 1/82), and administered intraperitoneally 1 hour before infection with anti-IL-18 monoclonal antibodies (0.25 mg/mouse). In a subsequent set of experiments, mice infected with a suboptimal arthritogenic dose of GBS (4 x 10(6) CFU/mouse) were administered different doses of recombinant IL-18 for 4 days, starting 1 hour after infection. Mortality, evolution of arthritis, bacterial clearance, joint histopathology, and cytokine production were examined in infected mice that did or did not receive treatment with anti-IL-18 antibodies or IL-18.

RESULTS

IL-18 was produced during GBS infection. Neutralization of IL-18 resulted in a decrease in mortality rates, and in the incidence and severity of arthritis. Amelioration of arthritis was accompanied by a dramatic reduction in local IL-1 beta, IL-6, macrophage inflammatory protein 1 alpha (MIP-1 alpha) and MIP-2 production, and reduced bacterial burden. Administration of exogenous IL-18 resulted in increased mortality rates and increased incidence and severity of GBS arthritis, concomitant with a higher number of GBS and increased levels of IL-6, IL-1 beta, MIP-1 beta, and MIP-2 production in the joints.

CONCLUSION

The present study indicated some involvement of IL-18 in the pathogenesis of GBS-induced arthritis. The role of IL-18 in joint pathology is shown by a regulatory effect on inflammatory mediator levels and local cell influx. Thus, IL-18 should be regarded as a potential therapeutic target in GBS infection and arthritis.

Role of macrophages in experimental group B streptococcal arthritis

Septic arthritis is a clinical manifestation of group B Streptococcus (GBS) infection in both neonates and adults. Because macrophages are known to participate in tissue injury, the role of this cell population in GBS-induced arthritis was investigated. Mice were rendered monocytopenic by administration of etoposide, a drug that selectively depletes the monocyte/macrophage population and then injected with GBS (1 x 10(7) colony-forming units per mouse). Appearance of arthritis, mortality, GBS growth in the organs, and local and systemic cytokine production were examined. Etoposide-treated mice had a significantly less severe arthritis than control animals. Histopathological analysis of the joints confirmed clinical observations. Decreased joint levels of the proinflammatory cytokines interleukin 1 (IL-1) beta and IL-6 accompanied the less severe development of arthritis in monocytopenic mice. In contrast, mortality was increased in the etoposide-treated mice compared with controls. Monocytopenic mice exhibited elevated bacterial load in the blood and kidneys at all time points examined. These results indicate that lack of macrophages leads to less severe joint lesions, but also results in impaired clearance of bacteria, and consequent enhancement of mortality rates.

Regulatory role of interleukin-10 in experimental group B streptococcal arthritis

Intravenous inoculation of CD-1 mice with 10(7) CFU of type IV group B Streptococcus (GBS) results in a high incidence of diffuse septic arthritis, associated with high levels of systemic and local production of interleukin-1beta (IL-1beta) and IL-6. In this study, the role of the anti-inflammatory cytokine IL-10 in the evolution of GBS systemic infection and arthritis was evaluated. IL-10 production was evident in sera and joints of GBS-infected mice. Neutralization of endogenous IL-10 by administration of anti-IL-10 antibodies (1 mg/mouse) at the time of infection resulted in worsening of articular lesions and 60% mortality associated with early sustained production of IL-6, IL-1beta, and tumor necrosis factor alpha (TNF-alpha). The effect of IL-10 supplementation was assessed by administering IL-10 (100, 200, or 400 ng/mouse) once a day for 5 days, starting 1 h after infection. Treatment with IL-10 had a beneficial effect on GBS arthritis, and there was a clear-cut dose dependence. The decrease in pathology was associated with a significant reduction in IL-6, IL-1beta, and TNF-alpha production. Histological findings showed limited periarticular inflammation and a few-cell influx in the articular cavity of IL-10-treated mice, confirming clinical observations. In conclusion, this study provides further information concerning the role of IL-10 in regulating the immune response and inflammation and calls attention to the potential therapeutic use of IL-10 in GBS arthritis.

The beneficial effect of interleukin-12 on arthritis induced by group B streptococci is mediated by interferon-gamma and interleukin-10 production

OBJECTIVE

To assess the effect of interleukin-12 (IL-12) administration on the evolution of systemic infection and septic arthritis induced by group B streptococci (GBS) in mice.

METHODS

CD1 mice were inoculated intravenously with arthritogenic strain 1/82 of type IV GBS. Exogenous murine IL-12 was administered intraperitoneally 18 hours or 5 days after infection with 1 x 10(7) GBS, at doses ranging from 0.5 to 2.5 microg per mouse. Mice were monitored daily for survival and for signs of arthritis. In a subsequent set of experiments, mice were killed at selected times for examination of bacterial clearance, histopathologic changes in the joints, and cytokine production.

RESULTS

IL-12 administration before the onset of clinical signs had a beneficial effect on GBS-induced arthritis and was clearly dose-dependent. The 2.5-microg dose per mouse totally prevented death from GBS-induced arthritis. The decrease in pathology was associated with a reduction of the bacterial burden and a change in the cytokine profile. In particular, systemic and joint levels of interferon-gamma (IFN gamma) and IL-10 significantly increased in mice treated with IL-12, whereas a decrease in IL-6 and IL-1 beta production was observed. The beneficial effects of IL-12, in terms of the incidence and severity of articular lesions, were reversed by coadministration of anti-IFN gamma or anti-IL-10-neutralizing antibodies.

CONCLUSION

The findings of this study demonstrate that IL-12 is important in controlling the cytokine production that leads to the evolution of GBS-induced experimental arthritis. The amelioration of articular lesions is mostly attributable to IL-12-induced IFN gamma, but with a relevant participation of IL-12-induced IL-10.

Influence of interferon-gamma administration on the severity of experimental group B streptococcal arthritis

OBJECTIVE

To assess the effect of interferon-gamma (IFNgamma) administration on the evolution of systemic infection and septic arthritis induced by group B streptococci (GBS) in mice.

METHODS

CD1 mice were inoculated intravenously with arthritogenic strain 1/82 of type IV GBS. Exogenous murine IFNgamma or anti-IFNgamma monoclonal antibodies were administered intravenously either 2 hours (-2 hours) before or 18 hours after infection with 1 x 10(7) GBS. Mice were monitored daily for survival and for signs of arthritis. In a subsequent set of experiments, mice were killed at selected times for examination of bacterial clearance, joint histopathology, and cytokine production.

RESULTS

Mortality in mice treated with IFNgamma at -2 hours was 100%, compared with 20% in those treated at 18 hours and with 40% in controls. As indicated by the arthritis score, mice treated with IFNgamma at -2 hours developed early and more severe arthritis, whereas those treated at 18 hours had milder arthritis compared with infected controls. Less severe joint pathology in the mice treated with IFNgamma at 18 hours correlated with low levels of interleukin-6 (IL-6) and IL-1beta and a low bacterial load in the joints, whereas rapid onset and worsening of articular lesions in those treated at -2 hours corresponded to early and sustained levels of IL-6.

CONCLUSION

The findings of this study demonstrate that the effects mediated by IFNgamma on GBS-induced arthritis may be detrimental or beneficial, depending on the time of administration of IFNgamma in relation to infection with the antigen.

Age-associated increased interleukin-6 gene expression, late-life diseases, and frailty

Interleukin-6 (IL-6) is a proinflammatory cytokine that is normally tightly regulated and expressed at low levels, except during infection, trauma, or other stress. Among several factors that down-regulate IL-6 gene expression are estrogen and testosterone. After menopause or andropause, IL-6 levels are elevated, even in the absence of infection, trauma, or stress. IL-6 is a potent mediator of inflammatory processes, and it has been proposed that the age-associated increase in IL-6 accounts for certain of the phenotypic changes of advanced age, particularly those that resemble chronic inflammatory disease [decreased lean body mass, osteopenia, low-grade anemia, decreased serum albumin and cholesterol, and increased inflammatory proteins such as C-reactive protein (CRP) and serum amyloid A]. Furthermore, the age-associated rise in IL-6 has been linked to lymphoproliferative disorders, multiple myeloma, osteoporosis, and Alzheimer's disease. This overview discusses the data relating IL-6 to age-associated diseases and to frailty. Like the syndrome of inappropriate antidiuretic hormone, it is possible that certain clinically important late-life changes are due to an inappropriate presence of IL-6.

Alpha-toxin and gamma-toxin jointly promote Staphylococcus aureus virulence in murine septic arthritis

Septic arthritis is a common and feared complication of staphylococcal infections. Staphylococcus aureus produces a number of potential virulence factors including certain adhesins and enterotoxins. In this study we have assessed the roles of cytolytic toxins in the development of septic arthritis by inoculating mice with S. aureus wild-type strain 8325-4 or isogenic mutants differing in the expression of alpha-, beta-, and gamma-toxin production patterns. Mice inoculated with either an alpha- or beta-toxin mutant showed degrees of inflammation, joint damage, and weight decrease similar to wild-type-inoculated mice. In contrast, mice inoculated with either double (alpha- and gamma-toxin-deficient)- or triple (alpha-, beta-, and gamma-toxin-deficient)-mutant S. aureus strains showed lower frequency and severity of arthritis, measured both clinically and histologically, than mice inoculated with the wild-type strain. We conclude that simultaneous production of alpha- and gamma-toxin is a virulence factor in S. aureus arthritis.

Endothelin subtype A receptor antagonist induces osteopenia in growing rats

Previous studies suggested that endothelin (ET) peptides are involved in bone metabolism. We examined the effects of long-term blockade of the ET(A) receptor, a receptor subtype primarily involved in the anabolic actions of ET, on bone mineral status in growing rats. Eight-week-old rats injected intraperitoneally with FR139317 50 mg/kg body weight, a specific ET(A) receptor antagonist, for 2 or 4 weeks were compared with control rats injected with vehicle only. Treatment with FR139317 caused a significant decrease in bone mass in the lumbar spine as determined by dual-energy x-ray absorptiometry (DXA). FR139317-induced osteopenia was associated with a significant decrease in the serum osteocalcin concentration but no change in the urinary excretion of pyridinium cross-links of collagen. Our findings indicate that long-term blockade of the ET(A) receptor reduces bone formation and induces osteopenia in growing rats. Our results suggest that ET produced by vascular endothelial cells plays an important role in bone growth and metabolism in vivo.

Immunologic aspects of osteoporosis

Osteoporosis is a major cause of morbidity in older people. There are a large number of risk factors for the development of osteoporosis. However, these risk factors eventually must mediate their effects through modulation of bone remodeling. A variety of compounds including hormones and nutrients modulate bone remodeling. In addition to these well-characterized substances, the immune system plays a role in bone remodeling through pro-inflammatory cytokines. Specifically, interleukin-1 (IL-1), IL-11, interferon-g are known to influence osteoclasts and osteoblasts. Recently, the cytokine IL-6 has joined ranks with these cytokines as a bone reactive agent. IL-6 has been shown to increase with age and menopause. Additionally, murine models suggest that IL-6 plays a central role in bone resorption. Finally, in vitro studies demonstrate that IL-6 induces osteoclast activity. In this review, we will discuss the pathogenesis of osteoporosis in the context of aging and IL-6.

Lack of autocrine effects of IL-6 on human bone marrow stromal osteoprogenitor cells

Interleukin-6 (IL-6) produced by osteoblastic cells plays an important role in the regulation of bone remodeling, mainly by stimulating osteoclast action. Although the IL-6 receptor is also found in osteoblastic cells, whether IL-6 exerts autocrine effects on osteoblastic cells is a matter of debate. This led us to study the effects of IL-6 on proliferation, osteoblastic activity as well as mRNA expression of various osteoblastic proteins in human bone marrow stromal osteoprogenitor cells (hBMSC). IL-6 did not affect cell proliferation assessed by [3H]-thymidine incorporation and osteoblastic activity determined by alkaline phosphatase activity and 45Ca incorporation. The expression of mRNAs for alkaline phosphatase, alpha 1 (I)-collagen, osteopontin and decorin also did not change significantly by IL-6 treatment. These results show that IL-6 does not have a significant autocrine role in regard to proliferation and osteoblastic activity of hBMSC.

Interleukin-6 inhibits long-term potentiation in rat hippocampal slices

The effects of recombinant human interleukin-6 (rhIL-6) on long-term potentiation (LTP) induced in the Schaffer collateral/commissural-CA1 pathway were examined using rat hippocampal slices. Field excitatory postsynaptic potential was recorded in the stratum radiatum of the CA1 region. Ten-min applications of rhIL-6 (50-2000 U/ml), started 5 min before the tetanus, significantly inhibited the induction of LTP, and in high doses of rhIL-6 also inhibited short-term potentiation (over 200 U/ml) and post-tetanic potentiation (over 500 U/ml). The effects of rhIL-6 (500 U/ml) were completely abolished by the preincubation of the slices with monoclonal anti-IL-6 receptor antibody (16 microg/ml) for 2 h. Heat-inactivated rhIL-6 had no effect on the synaptic potentiation. RhIL-6 affected neither the previously established LTP nor the basal synaptic transmission. These findings indicated that rhIL-6 modulated synaptic potentiation through the IL-6 receptor-mediated process in the hippocampus, probably by affecting post- and presynaptic sites in the CA1 region. The possible mechanisms of the IL-6-induced suppression of the synaptic potentiation were discussed.

Proliferating cells in the primary spongiosa express osteoblastic phenotype in vitro

We have shown that intermittent parathyroid hormone (PTH) treatment targets proliferating cells in the primary spongiosa of trabecular bone of young rats, resulting in an increased number of osteoblasts. To further characterize these proliferating osteoprogenitor cells, bromodeoxyuridine (BrdUrd) incorporated in vivo, was used as a marker to identify and isolate cells for in vitro studies. Proliferating cells were labeled in vivo in young rats with BrdUrd and 24 h later were isolated by trypsinization of sections of the primary spongiosa of the distal femur metaphysis. Within 12 h of isolation, BrdUrd+ cells formed distinct foci containing 20-500 cells with fibroblast morphology. Stimulation of proliferation as determined by [3H]-thymidine incorporation was observed for these cells in response to fetal bovine serum, platelet derived growth factor, and transforming growth factor beta-1. Neither insulin-like growth factor-1 (IGF-1) nor insulin stimulated proliferation PTH (1-34) and dexamethasone inhibited proliferation. The effects of PTH and dexamethasone were additive. Cells expressed the osteoblast phenotype as evidenced by synthesis of type I collagen, expression of high alkaline phosphatase activity, and production of increased intracellular cAMP in response to PTH (1-34). Confluent cell aggregates spontaneously formed mineralized nodules within 4-7 days, in the absence of inducers. These observations suggest that the primary spongiosa cells recapitulates the differentiation process in vitro in an accelerated fashion and may serve as a useful model to study osteoblast differentiation.

Role of the staphylococcal accessory gene regulator (sar) in septic arthritis

Staphylococcus aureus arthritis is a highly erosive disease in which both host and bacterial factors are of importance for its induction and progression. At the transcriptional level, three known loci act in regulating production of exoproteins and expression of cell wall structures. The aim of our study was to assess the role of the sar locus as a virulence determinant in the pathogenesis of septic arthritis. A recently established murine model of hematogenously spread S. aureus arthritis was employed. S. aureus strains, isogenic for the sar locus, were inoculated intravenously into NMRI mice, and the clinical, bacteriological, serological, and histopathological progression of the disease was studied. Within 1 week after inoculation of bacteria, the frequency of arthritis was 79% in the group of mice inoculated with the sar+ strain, whereas the corresponding frequency in sar mutants was 21% (P < 0.01). Mice inoculated with the sar+ staphylococcal strain exhibited a more pronounced T- and B-lymphocyte activation than those inoculated with the sar mutant, evidenced by splenomegaly, polyclonal B-cell activation, and high serum levels of interleukin 6 and gamma interferon. Also, infection with sar+ staphylococci induced a pronounced weight loss. To assess the relationship between clinical signs and spread of bacteria, we analyzed the homing pattern and persistence of S. aureus in host tissues. Kidneys and joints from sar+-inoculated subjects displayed a higher degree of bacterial persistence than other organs. Our results suggest that molecules controlled by the sar locus are important virulence determinants in the induction and progression of septic arthritis.

In vivo, human parathyroid hormone fragment (hPTH 1-34) transiently stimulates immediate early response gene expression, but not proliferation, in trabecular bone cells of young rats

Intermittent PTH increases trabecular bone mass in vivo by stimulating osteoblast differentiation to increase bone formation. The molecular events that mediate the anabolic effect of PTH on osteoblasts have not been characterized. We investigated if PTH regulated mRNA expression of proto-oncogenes, c-fos, c-jun, and c-myc, early response genes that have been shown to be involved in the regulation of both cell proliferation and differentiation. As PTH also regulates the early expression of the cytokine, interleukin-6 (IL-6), in bone cells in vitro, we also investigated if this occurred in vivo, in concert with the other early response genes. Northern blot hybridization was used to analyze mRNA expression in the metaphysis of the distal femur of young rats. To determine the proliferative state in these femurs, mRNA expression of the cell proliferation marker histone, H4, was assessed. Subcutaneous administration of a single injection of human PTH (1-34) at 8 micrograms/100 g, a dose known to increase bone forming surfaces, induced rapid and transient expression of c-fos, c-jun, c-myc, and IL-6 mRNA. A second novel transcript for IL-6 was detected, but its significance remains unknown. Induction of all these messages was evident by 1 h; the levels of mRNA returned to baseline after 3-6 h. Concurrently, PTH had a small inhibitory effect on the expression of histone H4 mRNA. We conclude that, in vivo, PTH upregulates cell differentiation in trabecular bone by transient stimulation of the early response genes and IL-6, while downregulating cell proliferation.

Preferential induction of septic arthritis and mortality by superantigen-producing staphylococci

Staphylococcal enterotoxins A through D (SEA through SED) and toxic shock syndrome toxin-1 display superantigen properties, i.e., they stimulate a great fraction of T cells expressing certain T-cell receptor V beta sequences. Using a newly established rat model of septic Staphylococcus aureus arthritis, we have recently shown that an S. aureus strain producing SEA showed marked arthritogenic properties. In the present study we decided to employ another five S. aureus strains, each one producing a distinct exotoxin. Almost all rats injected with superantigen-producing strains developed arthritis. In contrast, only 20% of rats injected with an S. aureus strain lacking superantigen production displayed mild and transient arthritis. Mortality was preferentially induced among the rats inoculated with the S. aureus strains producing SEB and SED. This study emphasizes that superantigen production is an important virulence factor in the development of septic S. aureus arthritis. Differences concerning mortality between staphylococcal strains producing different exotoxins may be dependent on the degree of activation of the immune system.