BRIEF REPORT Serum level of osteopontin as an inflammatory marker does not indicate disease activity or responsiveness to therapeutic treatments in patients with rheumatoid arthritis Hye-In Ji & Sang-Hoon Lee & Ran Song & Hyung-In Yang & Yeon-Ah Lee & Seung-Jae Hong & Somi Kim & Yong-Beom Park & Soo-Kon Lee & Myung Chul Yoo & Kyoung Soo Kim Received: 21 January 2013 /Revised: 10 June 2013 /Accepted: 18 August 2013 # Clinical Rheumatology 2013 Abstract Osteopontin (OPN) is known to be significantly involved in the pathogenesis of rheumatoid arthritis (RA). This study aimed to evaluate if the serum concentration of OPN in patients with RA before and after therapeutic treat- ments was correlated to disease activity and response to ther- apy. Blood samples from 40 patients with RA were collected at baseline and six months after starting treatment with disease-modifying antirheumatic drugs (DMARDs) and/or tumor necrosis factor (TNF)-α blockers. Serum levels of OPN were measured by ELISA. At baseline, the serum OPN level in RA patients was significantly higher than that of the healthy group. The OPN level at baseline in RA patients with severe disease activity as evaluated by DAS28 was slightly higher than that of those with moderate disease activity. The serum OPN level in RA patients was not significantly corre- lated with the DAS28 level. The serum OPN level in both responders and non-responders after therapy was significantly decreased regardless of responsiveness to therapy. Also, the OPN level at baseline did not affect the responsiveness to therapeutic treatments. In conclusion, serum OPN level was not correlated with disease activity or responsiveness of RA patients to therapeutic treatments. Keywords Disease-modifying antirheumatic drugs (DMARDs) . Osteopontin (OPN) . Rheumatoid arthritis (RA) . TNF blocker Introduction Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by synovial inflammation in which several inflam- matory cytokines such as tumor necrosis factor (TNF)-α, IL-1β, and IL-6 are involved [1]. Besides proinflammatory cytokines, adipokines such as adiponectin and leptin are involved in the pathogenesis and perpetuation of RA [2]. In addition, osteopon- tin (OPN), which is a multifunctional molecule highly expressed in chronic inflammatory and autoimmune diseases, is believed to exacerbate inflammation in several chronic inflammatory diseases such as RA [3, 4], experimental autoimmune enceph- alomyelitis, multiple sclerosis [5], allergic disease [6], and car- diovascular disease [7]. It also regulates cytokine production in macrophages, dendritic cells, and T cells. Thus, OPN has been classified as T-helper 1 cytokine. It is highly expressed by activated T cells, dendritic cells, and macrophages during in- flammation. Furthermore, the function of OPN is modulated by digestion of at least two classes of proteases: thrombin and matrix metalloproteases (MMPs) [8]. The thrombin-cleaved form of OPN is involved in the pathogenesis of various inflam- matory disorders, and its concentration in RA synovial fluid samples was found to be approximately 30-fold higher com- pared to OA samples, even though there was no difference between the concentration of full-length OPN in the synovial H.<I. Ji : M. C. Yoo : K. S. Kim (*) East-West Bone & Joint Research Institute, Kyung Hee University, 149 Sangil-dong, Gangdong-gu Seoul 134-727, Republic of Korea e-mail: labrea46@yahoo.co.kr S.<H. Lee : R. Song : H.<I. Yang Division of Rheumatology, Department of Internal Medicine, Kyung Hee University Hospital at Gandong, 149 Sangil-dong, Gangdong-gu Seoul 134-727, Republic of Korea Y.<A. Lee : S.<J. Hong : S. Kim Division of Rheumatology, Department of Internal Medicine, College of Medicine, Kyung Hee University, Hoegi-dong, Dongdaemun-gu Seoul 130-702, Republic of Korea Y.<B. Park : S.<K. Lee Divsion of Rheumatology, Department of Internal Medicine, Yonsei University College of Medicine, 250 Sungsanno, Seodaemoon-gu Seoul 120-752, Republic of Korea Clin Rheumatol DOI 10.1007/s10067-013-2375-3