Background Steroids are commonly used for the treatment of chronic inflammatory diseases. Although the anti-inflammatory effects of steroids are to be expected, the prevalence of side-effects caused by high dosages of steroids is also high. Therefore, it is very important to taper the dosage of steroids. However, patients with chronic inflammatory disease sometimes develop a resistance to therapy with steroids, resulting in high dosages of steroids. Because elevated levels of IL-6 are found in these patients, it is thought that IL-6 might directly induce steroid-resistance.
Objectives We examined whether IL-6 attenuates the anti-inflammatory effect of steroids in vivo and in vitro.
Methods 1) To prepare a collagen-induced arthritis (CIA) model, DBA/1J mice were immunized with bovine type II collagen, and 21 days later (Day 21) given once again a booster injection. Prednisolone (PSL) was intraperitoneally administered at doses of 1, 3, and 6 mg/kg five times a week from Day 21. Rat anti-mouse IL-6R monoclonal antibody (MR16-1) was intraperitoneally administered once on Day 21. Clinical symptoms of arthritis were evaluated by observation and expressed as an arthritis score on a scale of 0–4 for each limb.
2) THP-1 macrophages were pretreated with 100 ng/mL of IL-6 or culture medium for 24 h. After medium replacement, cells were stimulated by lipopolysaccharide (LPS) in the presence or absence of 1 μM of dexamethasone (DEX) for another 3 h. After culture, to evaluate the inflammatory response, expression levels of CCL20 mRNA were determined by RT-PCR. Moreover, the influence of IL-6 on DEX-induced nuclear translocation of glucocorticoid receptor (GR) was examined by immunostaining and western blotting of GR.
Results PSL dose-dependently reduced arthritis score in the CIA model on Day 33 (PSL 1 mg/kg: 72% of control; PSL 3 mg/kg: 51%; PSL 6 mg/kg: 21%). MR16-1 in combination with low doses of PSL improved clinical symptoms significantly better than the same dose of PSL alone on Day 33 (PSL 1 mg/kg: 43% of control; PSL 3 mg/kg: 25%), even though administration of MR16-1 alone resulted in no improvement. On the other hand, no significant difference in arthritis score was found between PSL 6 mg/kg alone and in combination with MR16-1 on Day 33 (PSL 6 mg/kg: 21% of control; PLS 6 mg/kg plus MR16-1: 17%). Interestingly, however, the combination of PSL 6 mg/kg and MR16-1 reduced symptoms significantly better than PSL 6 mg/kg alone in the later periods from Day 38 to Day 50. To explore how MR16-1 could improve the anti-inflammatory effect of PSL, we next examined the influence of IL-6 on DEX activity, which suppresses the LPS-mediated inflammatory response in macrophages. The increased expression of CCL20 induced by LPS was clearly suppressed by DEX, but IL-6 pretreatment attenuated the inhibitory effect of DEX. Furthermore, IL-6 pretreatment decreased GR expression and inhibited GR nuclear translocation.
Conclusions We demonstrated that IL-6 blockade enhanced the therapeutic effect of steroids, possibly through restoring GR expression and nuclear translocation of GR repressed by IL-6. It might be possible to taper the dosage of steroids by IL-6 blockade.
Disclosure of Interest None Declared