Rheumatoid arthritis is a common disease that causes important suffering, disability, and increased mortality. There is a great need for new insight into disease mechanisms. Nitric oxide (NO) plays a role in inflammatory disorders, including RA. The factor(s) that induces mononuclear cells in humans to express the inducible NO synthase (NOS2) and to produce NO has not fully been clearly identified. Our recent studies have indicated that interferon-alpha (IFN-alpha) potently """"""""activates"""""""" monocytes to express NOS2 and produce NO. We hypothesize that IFN-alpha is overproduced systemically and locally (in joint tissues) in RA and that this contributes to the. NOS2 activation and inflammation seen in patients with RA. The anti-inflammatory actions of tetracycline-related drugs are independent of their anti-microbial actions. While these drugs inhibit matrix metalloproteinases, they also inhibit expression of NOS2 in vitro. We hypothesize that the NOS2 inhibitory actions account in part for their anti-inflammatory effects in vivo. Patients with RA, because of pain, splinting, and joint deformities place abnormal mechanical stresses on their articular cartilage. We showed that mechanical stress induces NO production by that cartilage. We hypothesize that NO is overproduced in cartilage of RA patients (as compared to that of normal subjects or subjects with osteoarthritis) in response to mechanical stress, and that the induced NO alters cartilage homeostasis in RA.
Our aims are to (1) determine the role of IFN-alpha in the """"""""activation"""""""" of human mononuclear phagocytes for NOS2 expression and NO production in RA; (2) determine' whether treatment of RA patients with doxycycline reduces their blood mononuclear cell NOS expression and NO production; and (3) determine the role of mechanical stress on cartilage NOS expression and NO production in RA. Accomplishing our proposed work will answer important questions regarding NO, NOS2, IFN-alpha, and mechanical stress, and their inter- relationships in RA. These answers will provide important new information that may lead to new approaches to the treatment of RA.
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