Sinomenine is a promising analgesic and anti-hyperalgesic for pain and hypersensitivity in rheumatoid arthritis

Abstract

In this issue of the Scandinavian Journal of Pain, Tianle Gao nd coworkers in Zsuzsanna Wiesenfeld-Hallin’s research group t Karolinska Institutet report on the effect of sinomenine to lleviate mechanical hypersensitivity in mice with experimentallynduced rheumatoid arthritis (RA) [1]. Sinomenine is isolated from he climbing plant Sinomenium acutum, and it is used in tradiional medicine in Asia for its beneficial effects on auto immune iseases, especially RA [2]. In animal models of arthritis, sinomeine counteracts joint destruction and reduces several signs of nflammation including joint swelling, erythrocyte sedimentation ate, production of antibodies, and secretion of cytokines [3,4]. esides its anti-inflammatory property, sinomenine also reduces ain behaviour in nociceptive, inflammatory, and neuropathic pain odels in rodents [5–8]. Gao and co-workers are now following p the anti-nociceptive effect on inflammation-induced hyperensitivity with further analysis of the effect of sinomenine on echanical hypersensitivity associated with RA [1]. Pain is a domiating symptom in human RA and the hyperalgesic symptoms often recede the inflammatory signs, and continues after the inflammaion subsides. This suggests that it is not only inflammation that is nvolved in the pathophysiology of pain in RA [9]. Gao and co-workers used the collagen antibody induced arthriis (CAIA) model to induce RA-like symptoms in mice, including oint inflammation and localized mechanical hypersensitivity nd/or spread mechanical hypersensitivity. In this model, a cockail of five antibodies against collagen is injected intravenously after he baseline levels of mechanical sensitivity have been established sing von Frey filaments. The immune reaction is later boosted by n intraperitoneal injection of lipopolysaccharide on day 5 after he cocktail injection. This induces profound swelling and redness f the paws and ankles. These symptoms peak at day 15 after he cocktail injection (termed the inflammatory phase). Gao and o-workers studied the effects of sinomenine during the inflamatory phase as well as in the post-inflammatory phase (days 5–54 after the cocktail injection) when the inflammatory signs ave subsided but mechanical hypersensitivity continues [1]. They