Biological therapies, or biologics, are a class of medications that are specifically designed to target molecules from defined pathogenetic pathways for therapeutic purposes. Currently, the most widely used biological agents to treat inflammatory arthritides are mainly of the anti- tumour necrosis factor alpha (anti-TNFα) group. Other biological agents that are less widely used in the clinic include: interleukin-1 inhibitors (Anakinra), T cell co-stimulatory inhibitors, CTLA- 4 (Abatacept) and B lymphocyte depletion agents (Rituximab). TNFα blockers are more effective than conventional disease- modifying anti rheumatic drugs (DMARDs) and in combination with methotrexate induce remission in nearly half of the patients with rheumatoid arthritis (RA). Unlike conventional DMARDS, biological therapies specifically target molecular or cellular pathway central to disease development. Biological therapies are a true example of the translation of research from the laboratory bench to the bedside. At present, TNFα blockers are known to decrease joint inflammation and bone erosions but their effects on bone resorption are still being elucidated. Further, new emerging targets for biological therapy are being assessed, with several recent studies showing key roles played by various other cytokines and molecules in the pathophysiology of inflammatory joint damage. Importantly, in addition to the therapeutic benefits these studies reveal the importance of key cytokines and other target molecules in normal bone metabolism and homeostasis. This article will review current knowledge on the effects of disease processes and therapeutic agents on bone metabolism and homeostasis in arthritic diseases.
Keywords: inflammatory arthritides, anti- tumour necrosis factor alpha (anti-TNFα), bone metabolism, Biological therapies, cytokines, homeostasis, pathophysiology
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