Studies of molecular mechanisms of action of TNF antagonists in rheumatoid arthritis
Author: Catrina, Anca Irinel
Date: 2004-12-17
Location: Föreläsningssalen Centrum för Molekylär Medicin (CMM) L8:00, Karolinska Universitetssjukhuset
Time: 9.00
Department: Institutionen för medicin / Department of Medicine
View/ Open:
Thesis (802.2Kb)
Abstract
Rheumatoid arthritis (RA) is a common chronic inflammatory disease
characterized by progressive bone destruction that leads to joint
deformity and physical disability. Even though several therapeutic drugs
are available, none have emerged as an ideal RA treatment that delays
joint destruction and halts disease progression. A new class of drugs,
tumor necrosis factor (TNF) antagonists, has recently been introduced in
clinical practice: infliximab (chimeric anti-TNF antibody), etanercept
(soluble TNF receptor) and adalimumab (fully human anti-TNF antibody).
The exact mechanisms of action of these drugs are still poorly
understood, even though the important role played by cytokines in RA
pathogenesis is the main rationale behind using them for treatment. This
thesis investigates the molecular mechanisms of action for TNF
antagonists in RA with a focus on synovial inflammation and bone
destruction.
A major feature of RA is synovial inflammation with local accumulation of immune cells through increased cell influx and decreased clearance of resident cells. We demonstrated that early RA, which is characterized by important macrophage infiltration, is associated with low levels of synovial apoptosis. We also identified macrophage infiltration and synovial expression of the anti-apoptotic molecule FLIP (FLICE inhibitory protein) as determinant factors of synovial apoptosis. As apoptosis is a potential relevant mechanism for RA, we investigated if treatment with TNF antagonists modulates this process. We demonstrated that therapy with both infliximab and etanercept induces apoptosis of macrophages but not of lymphocytes in RA joints. Blood-derived macrophages were less susceptible to anti-TNF induced apoptosis, suggesting that induction of apoptosis through TNF blockade is specific for an inflammatory milieu such as the rheumatoid joint.
Synovial inflammation leads to bone destruction that is mediated through either an indirect mechanism induced through cytokine-mediated release of pro-destructive factors such as the matrix metalloproteinases (MMP)-tissue inhibitors of MMPs (TIMPs) system or a direct mechanism mediated through receptor activator of the nuclear factor-?B ligand (RANKL)-osteoprotegerin (OPG) system. We demonstrated that etanercept is able to decrease serum levels of MMPs and the ratio between MMPs and TIMP, which represents a potential mechanism involved in prevention of future development of joint damage. Moreover, baseline MMP-3 serum levels could predict the changes in disease activity during therapy. The RANKL/OPG system is considered to be the final denominator of bone remodeling. We demonstrated that treatment with both etanercept and infliximab increased synovial OPG expression without changes in RANKL expression. The synovial RANKL/OPG ratio thus decreased following therapy, the effect being more pronounced in the responders compared to non-responders to therapy.
In conclusion, we have demonstrated that TNF antagonists modulate important mechanisms implicated in synovial inflammation and bone destruction. We propose that therapies which target synovial TNF independent mechanisms, such as RANKL expression and lymphocyte apoptosis, are also valuable candidates for adjuvant therapy in RA.
A major feature of RA is synovial inflammation with local accumulation of immune cells through increased cell influx and decreased clearance of resident cells. We demonstrated that early RA, which is characterized by important macrophage infiltration, is associated with low levels of synovial apoptosis. We also identified macrophage infiltration and synovial expression of the anti-apoptotic molecule FLIP (FLICE inhibitory protein) as determinant factors of synovial apoptosis. As apoptosis is a potential relevant mechanism for RA, we investigated if treatment with TNF antagonists modulates this process. We demonstrated that therapy with both infliximab and etanercept induces apoptosis of macrophages but not of lymphocytes in RA joints. Blood-derived macrophages were less susceptible to anti-TNF induced apoptosis, suggesting that induction of apoptosis through TNF blockade is specific for an inflammatory milieu such as the rheumatoid joint.
Synovial inflammation leads to bone destruction that is mediated through either an indirect mechanism induced through cytokine-mediated release of pro-destructive factors such as the matrix metalloproteinases (MMP)-tissue inhibitors of MMPs (TIMPs) system or a direct mechanism mediated through receptor activator of the nuclear factor-?B ligand (RANKL)-osteoprotegerin (OPG) system. We demonstrated that etanercept is able to decrease serum levels of MMPs and the ratio between MMPs and TIMP, which represents a potential mechanism involved in prevention of future development of joint damage. Moreover, baseline MMP-3 serum levels could predict the changes in disease activity during therapy. The RANKL/OPG system is considered to be the final denominator of bone remodeling. We demonstrated that treatment with both etanercept and infliximab increased synovial OPG expression without changes in RANKL expression. The synovial RANKL/OPG ratio thus decreased following therapy, the effect being more pronounced in the responders compared to non-responders to therapy.
In conclusion, we have demonstrated that TNF antagonists modulate important mechanisms implicated in synovial inflammation and bone destruction. We propose that therapies which target synovial TNF independent mechanisms, such as RANKL expression and lymphocyte apoptosis, are also valuable candidates for adjuvant therapy in RA.
List of papers:
I. Catrina AI, Ulfgren AK, Lindblad S, Grondal L, Klareskog L (2002). Low levels of apoptosis and high FLIP expression in early rheumatoid arthritis synovium. Ann Rheum Dis. 61(10): 934-6.
Pubmed
II. Catrina AI, Trollmo C, af Klint E, Engstrom M, Lampa J, Hermansson Y, Klareskog L, Ulfgren AK (2004). Evidence that anti tumor nercrosis factor therapy with both etanercept and infliximab induces apoptosis but not lymphocytes in RA joints. Arthritis and Rheumatism. [Accepted]
View record in Web of Science®
III. Catrina AI, Lampa J, Ernestam S, af Klint E, Bratt J, Klareskog L, Ulfgren AK (2002). Anti-tumour necrosis factor (TNF)-alpha therapy (etanercept) down-regulates serum matrix metalloproteinase (MMP)-3 and MMP-1 in rheumatoid arthritis. Rheumatology. 41(5): 484-9.
Pubmed
IV. Catrina AI, af Klint E, Ernestam S, Catrina SB, Klareskog L, Ulfgren AK (2004). Anti TNF therapy induces synovial osteoprotegerin expression in rheumatoid arthritis. [Manuscript]
I. Catrina AI, Ulfgren AK, Lindblad S, Grondal L, Klareskog L (2002). Low levels of apoptosis and high FLIP expression in early rheumatoid arthritis synovium. Ann Rheum Dis. 61(10): 934-6.
Pubmed
II. Catrina AI, Trollmo C, af Klint E, Engstrom M, Lampa J, Hermansson Y, Klareskog L, Ulfgren AK (2004). Evidence that anti tumor nercrosis factor therapy with both etanercept and infliximab induces apoptosis but not lymphocytes in RA joints. Arthritis and Rheumatism. [Accepted]
View record in Web of Science®
III. Catrina AI, Lampa J, Ernestam S, af Klint E, Bratt J, Klareskog L, Ulfgren AK (2002). Anti-tumour necrosis factor (TNF)-alpha therapy (etanercept) down-regulates serum matrix metalloproteinase (MMP)-3 and MMP-1 in rheumatoid arthritis. Rheumatology. 41(5): 484-9.
Pubmed
IV. Catrina AI, af Klint E, Ernestam S, Catrina SB, Klareskog L, Ulfgren AK (2004). Anti TNF therapy induces synovial osteoprotegerin expression in rheumatoid arthritis. [Manuscript]
Issue date: 2004-11-26
Rights:
Publication year: 2004
ISBN: 91-7140-102-4
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