Interleukin-1β and Tumor Necrosis Factor-α Produce Distinct, Time-dependent Patterns of Acute Arthritis in the Rat Knee

Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) synergistically induce and sustain arthritis. Two competing hypotheses of arthritis induction are 1) that TNF preferentially mediates inflammation, whereas IL-1 impels bone destruction, or 2) that either cytokine controls the entire process. In this study, these propositions were tested in two experiments by instilling IL-1β or TNF-α into one knee of Lewis rats ( n = 6/group) to incite arthritis, after which semiquantitative scores for inflammation, bone resorption, osteoclasts, and cartilage integrity were acquired. In the induction study, IL-1β or TNF-α (3, 10, or 30 μg) was given once to incite arthritis. After 2 days, IL-1β induced significant, dose-dependent increases in inflammation (mild to marked), bone resorption (minimal to moderate), and osteoclasts (minimal to moderate). In contrast, TNF-α induced minimal to mild inflammation but had little impact on resorption or osteoclasts. Both IL-1 and TNF (≥10 μg) yielded mild cartilage degeneration. Most lesion scores in TNF-treated rats were significantly lower than those in animals given the same dose of IL-1β. In the persistence study, rats were injected once with IL-1 or TNF (10 μg) and maintained for 2, 3, or 7 days. IL-1β significantly enhanced inflammation (all 3 days), bone resorption (days 2 and 3), osteoclasts (days 2 and 3), and cartilage matrix loss (days 2 and 3), whereas TNF-α augmented inflammation (days 2 and 3) and cartilage degeneration (day 2) but not bone resorption or osteoclasts. Thus, both IL-1β and TNF-α can launch inflammation, but IL-1β drives skeletal destruction.

Duration of bone protection by a single osteoprotegerin injection in rats with adjuvant-induced arthritis

Daily osteoprotegerin (OPG) injection for 7 or more days prevents bone loss for 3 weeks in rats with adjuvant-induced arthritis (AdA). The present experiments defined the duration of bone protection in AdA provided by a single OPG bolus. Male Lewis rats received OPG at the onset or peak of clinical disease, after which bone mineral density (BMD), erosions, and osteoclasts were evaluated. An OPG bolus (4 mg/kg subcutaneously) at onset eliminated osteoclasts, preserved BMD for 7 days, and prevented bone erosions for 4 days. In contrast, an OPG bolus (1, 3, 10, or 30 mg/kg intravenously) given at the peak of disease eradicated osteoclasts in a dose-dependent manner but had no impact on bone integrity due to extensive pre-existing bone loss. These data indicate that one OPG injection will inhibit joint erosions for several days, and confirm that bone-sparing therapy must be initiated early in disease to protect joint integrity.

Anti-interleukin-1 and anti-tumor necrosis factor-alpha synergistically inhibit adjuvant arthritis in Lewis rats

Interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) play dominant roles in mediating the progression of many inflammatory joint diseases, including rheumatoid arthritis in humans, collagen-induced arthritis in mice and rats, and adjuvant arthritis in rats. Blockade of either cytokine partially controls these diseases. The present study investigated the value of combination anti-cytokine therapy in arthritis: the efficacy of IL-1 receptor antagonist (IL-1ra) and 30 kDa polyethylene glycol (PEG)-conjugated soluble TNF receptor type I (PEG sTNF-RI) given together was assessed in Lewis rats with adjuvant arthritis. Administration of either IL-1ra or PEG sTNF-RI partially alleviated joint inflammation, loss of bone mineral density, and loss of body weight. In contrast, combination of these anti-cytokine treatments exhibited a synergistic capacity to inhibit these changes, even when combining doses of IL-1ra and PEG sTNF-RI that did not affect lesion severity when used alone. Statistical analysis of these adjuvant arthritis data using the isobologram method proved that IL-1ra and PEG sTNF-RI were clearly synergistic in inhibiting inflammation, loss of bone mineral density, loss of body weight, and histopathologic parameters of inflammation and joint destruction. These results suggest that treating autoimmune arthritic diseases with combinations of anti-IL-1 and anti-TNF molecules will achieve superior efficacy compared to the use of a single class of anti-cytokine agent and may allow for dose reductions that could prove useful in minimizing potential side effects.

Activated T cells regulate bone loss and joint destruction in adjuvant arthritis through osteoprotegerin ligand

Bone remodelling and bone loss are controlled by a balance between the tumour necrosis factor family molecule osteoprotegerin ligand (OPGL) and its decoy receptor osteoprotegerin (OPG). In addition, OPGL regulates lymph node organogenesis, lymphocyte development and interactions between T cells and dendritic cells in the immune system. The OPGL receptor, RANK, is expressed on chondrocytes, osteoclast precursors and mature osteoclasts. OPGL expression in T cells is induced by antigen receptor engagement, which suggests that activated T cells may influence bone metabolism through OPGL and RANK. Here we report that activated T cells can directly trigger osteoclastogenesis through OPGL. Systemic activation of T cells in vivo leads to an OPGL-mediated increase in osteoclastogenesis and bone loss. In a T-cell-dependent model of rat adjuvant arthritis characterized by severe joint inflammation, bone and cartilage destruction and crippling, blocking of OPGL through osteoprotegerin treatment at the onset of disease prevents bone and cartilage destruction but not inflammation. These results show that both systemic and local T-cell activation can lead to OPGL production and subsequent bone loss, and they provide a novel paradigm for T cells as regulators of bone physiology.