Immunoregulatory mediators in the pathogenesis of rheumatoid arthritis

Pharmaceutical aspects of anti-inflammatory TNF-blocking drugs

Tumor necrosis factor (TNF) is a key regulator of inflammatory processes in several immune-mediated inflammatory diseases such as rheumatoid arthritis, ankylosing spondylitis, Crohn's disease, ulcerative colitis, psoriasis and psoriatic arthritis. Inactivating TNF has been found to be a plausible approach in treating these conditions. Two major strategies have been adopted by scientists to inactivate TNF: one is to use monoclonal antibodies (mAbs) that bind to TNF, and the other is to use fusion proteins that bind to TNF, both inactivate TNF and help to prevent TNF-mediated inflammatory processes. Monoclonal antibodies (mAbs) are biological products that selectively bind to specific antigen molecules, and fusion proteins are soluble receptors that bind to TNF. These types of drugs are generally known as biologics and there has been an explosion in the development and testing of biologics since the 1994 US approval and launch of abciximab, a mAb that binds to GPIIb/IIIa on platelets. Anti-TNF drugs that are currently approved by FDA for treating inflammatory conditions include adalimumab, certolizumab pegol, golimumab, infliximab and etanercept. Since these agents are complex protein molecules, the pharmacodynamics and pharmacokinetics of these drugs are different from small-molecule anti-inflammatory agents. This review focuses on the pharmaceutical aspects of these drugs such as mechanism of action, adverse effects, pharmacokinetics and drug interactions. An effort was also taken to compare the pharmacodynamics and pharmacokinetic properties of these drugs, with the available data at this time.

The tumor necrosis factor-{alpha}-blocking agent infliximab inhibits interleukin 1beta (IL-1beta) and IL-6 gene expression in human osteoblastic cells

OBJECTIVE

Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine involved in the pathogenesis of several rheumatic diseases, including rheumatoid arthritis (RA), associated with systemic bone loss and subchondral bone erosions. TNF-alpha-blocking agents such as infliximab have been successful in treatment of disease-modifying antirheumatic drug-resistant rheumatic diseases. Infliximab therapy in RA also had beneficial effects on local bone destruction and bone mineral density. We assessed effects of infliximab treatment on the bone tissue compartment and cytokine profile expression in vitro.

METHODS

Osteoblast-like cells were exposed for 24 h to sera of RA patients collected at baseline and after 1 month (T1) and 3 years (T2) of infliximab treatment. Total RNA was extracted, and expression of interleukin 1beta (IL-1beta), IL-6, and osteoprotegerin (OPG) was measured by RT-PCR.

RESULTS

IL-1beta gene expression was significantly reduced by the T1 serum, and the same decrease was elicited by the T2 serum. IL-6 downregulation was evident with the T2 serum. OPG was unaffected.

CONCLUSION

The finding of downregulation of inflammatory cytokines was interesting, particularly IL-6, which plays a crucial role in arthritis-related bone loss due to its involvement in osteoclast recruitment and activation. These results may represent a biological explanation and a link for the clinical observation of the beneficial effects of anti-TNF-alpha agents on the progression of rheumatic diseases at the bone level.

Interleukin-17: A new bone acting cytokine in vitro

Interleukin-17 (IL-17) is a recently cloned cytokine that is exclusively produced by activated T cells, but its receptor has been found on several cells and tissues. Like other proinflammatory cytokines produced by activated T cells, IL-17 may affect osteoclastic resorption and thereby mediate bone destruction accompanying some inflammatory diseases. In the present study, we investigated whether osteogenic cells possess the receptor for IL-17 (IL-17R) and whether IL-17 affects osteoclastic resorption. We found that IL-17R mRNA is expressed both in mouse MC3T3-E1 osteoblastic cells and fetal mouse long bones, suggesting that osteogenic cells may be responsive to IL-17. In fetal mouse long bones, IL-17 had no effect on basal and IL-1beta-stimulated osteoclastic bone resorption, but when given together with tumor necrosis factor-alpha (TNF-alpha) it increased bone resorption dose dependently in serum-free conditions. In addition, IL-17 increased TNF-alpha-induced IL-1alpha, IL-1beta, and IL-6 mRNA expression in fetal mouse metatarsals and IL-1alpha and IL-6 mRNA expression in MC3T3-E1 cells. In conclusion, IL-17R mRNA was expressed by mouse osteoblastic cells and fetal mouse long bones, and IL-17 in combination with TNF-alpha, but not IL-1beta, increased osteoclastic resorption in vitro. IL-17 may therefore affect bone metabolism in pathological conditions characterized by the presence of activated T cells and TNF-alpha production such as rheumatoid arthritis and loosening of bone implants.

Clinical pharmacology and use of nonsteroidal anti-inflammatory drugs

This review informs clinicians about current clinical usage and pharmacokinetics of newer NSAIDs and aspirin. To understand the effects of these drugs, a review of prostaglandin synthesis and actions is provided.