Destruction of cartilage and bone are hallmarks of human rheumatoid
arthritis (RA), and controlling these erosive processes is the most challenging
objective in the treatment of RA. Systemic interleukin-4 treatment of
established murine collagen-induced arthritis suppressed disease activity and
protected against cartilage and bone destruction. Reduced cartilage pathology
was confirmed by both decreased serum cartilage oligomeric matrix protein
(COMP) and histological examination. In addition, radiological analysis
revealed that bone destruction was also partially prevented. Improved
suppression of joint swelling was achieved when interleukin-4 treatment was
combined with low-dose prednisolone treatment. Interestingly, synergistic
reduction of both serum COMP and inflammatory parameters was noted when
low-dose interleukin-4 was combined with prednisolone. Systemic treatment with
interleukin-4 appeared to be a protective therapy for cartilage and bone in
arthritis, and in combination with prednisolone at low dosages may offer an
alternative therapy in RA.
Introduction:
Rheumatoid arthritis (RA) is associated with an increased
production of a range of cytokines including tumour necrosis factor
(TNF)-α and interleukin (IL)-1, which display potent proinflammatory
actions that are thought to contribute to the pathogenesis of the disease.
Although TNF-α seems to be the major cytokine in the inflammatory process,
IL-1 is the key mediator with regard to cartilage and bone destruction. Apart
from direct blockade of IL-1/TNF, regulation can be exerted at the level of
modulatory cytokines such as IL-4 and IL-10. IL-4 is a pleiotropic T-cell
derived cytokine that can exert either suppressive or stimulatory effects on
different cell types, and was originally identified as a B-cell growth factor
and regulator of humoral immune pathways. IL-4 is produced by activated
CD4+ T cells and it promotes the maturation of Th2 cells. IL-4
stimulates proliferation, differentiation and activation of several cell types,
including fibroblasts, endothelial cells and epithelial cells. IL-4 is also
known to be a potent anti-inflammatory cytokine that acts by inhibiting the
synthesis of proinflammatory cytokines such as IL-1, TNF-α, IL-6, IL-8 and
IL-12 by macrophages and monocytes. Moreover, IL-4 stimulates the synthesis of
several cytokine inhibitors such as interleukin-1 receptor antagonist (IL-1Ra),
soluble IL-1-receptor type II and TNF receptors IL-4 suppresses
metalloproteinase production and stimulates tissue inhibitor of
metalloproteinase-1 production in human mononuclear phagocytes and cartilage
explants, indicating a protective effect of IL-4 towards extracellular matrix
degradation. Furthermore, IL-4 inhibits both osteoclast activity and survival,
and thereby blocks bone resorption in vitro. Of great importance is
that IL-4 could not be detected in synovial fluid or in tissues. This absence
of IL-4 in the joint probably contributes to the disturbance in the Th1/Th2
balance in chronic RA.
Collagen-induced arthritis (CIA) is a widely used model of
arthritis that displays several features of human RA. Recently it was
demonstrated that the onset of CIA is under stringent control of IL-4 and
IL-10. Furthermore, it was demonstrated that exposure to IL-4 during the
immunization stage reduced onset and severity of CIA. However, after cessation
of IL-4 treatment disease expression increased to control values.
Aims:
Because it was reported that IL-4 suppresses several
proinflammatory cytokines and matrix degrading enzymes and upregulates
inhibitors of both cytokines and catabolic enzymes, we investigated the tissue
protective effect of systemic IL-4 treatment using established murine CIA as a
model. Potential synergy of low dosages of anti-inflammatory
glucocorticosteroids and IL-4 was also evaluated.
Methods:
DBA-1J/Bom mice were immunized with bovine type II collagen and
boosted at day 21. Mice with established CIA were selected at day 28 after
immunization and treated for days with IL-4, prednisolone, or combinations of
prednisolone and IL-4. Arthritis score was monitored visually. Joint pathology
was evaluated by histology, radiology and serum cartilage oligomeric matrix
protein (COMP). In addition, serum levels of IL-1Ra and anticollagen antibodies
were determined.
Results:
Treatment of established CIA with IL-4 (1 μg/day) resulted
in suppression of disease activity as depicted in Figure 1. Of great interest is that, although 1 μg/day IL-4 had
only a moderate effect on the inflammatory component of the disease activity,
it strongly reduced cartilage pathology, as determined by histological
examination (Fig. 1). Moreover, serum COMP levels were
significantly reduced, confirming decreased cartilage involvement. In addition,
both histological and radiological analysis showed that bone destruction was
prevented (Fig. 1). Systemic IL-4 administration
increased serum IL-1Ra levels and reduced anticollagen type II antibody levels.
Treatment with low-dose IL-4 (0.1 μg/day) was ineffective in suppressing
disease score, serum COMP or joint destruction. Synergistic suppression of both
arthritis severity and COMP levels was noted when low-dose IL-4 was combined
with prednisolone (0.05 mg/kg/day), however, which in itself was not
effective.
Discussion:
In the present study, we demonstrate that systemic IL-4 treatment
ameliorates disease progression of established CIA. Although clinical disease
progression was only arrested and not reversed, clear protection against
cartilage and bone destruction was noted. This is in accord with findings in
both human RA and animal models of RA that show that inflammation and tissue
destruction sometimes are uncoupled processes. Of great importance is that,
although inflammation was still present, strong reduction in serum COMP was
found after exposure to IL-4. This indicated that serum COMP levels reflected
cartilage damage, although a limited contribution of the inflamed synovium
cannot be excluded.
Increased serum IL-1Ra level (twofold) was found after systemic
treatment with IL-4, but it is not likely that this could explain the
suppression of CIA. We and others have reported that high dosages of IL-1Ra are
needed for marked suppression of CIA. As reported previously, lower dosages of
IL-4 did not reduce clinical disease severity of established CIA. Of importance
is that combined treatment of low dosages of IL-4 and IL-10 appeared to have
more potent anti-inflammatory effects, and markedly protected against cartilage
destruction. Improved anti-inflammatory effect was achieved with
IL-4/prednisolone treatment. In addition, synergistic effects were found for
the reduction of cartilage and bone destruction. This indicates that systemic
IL-4/prednisolone treatment may provide a cartilage and bone protective therapy
for human RA.
