Objective: Ruxiang, or Gummi olibanum, an herbal medicine derived from the gum resin of Boswellia carterii Birdw. (BC) of the family Burseraceae, has been used traditionally in China to alleviate pain and reduce inflammation. The present study is an investigation of the effects of a BC extract on persistent hyperalgesia and edema in rats with peripheral inflammation.
Design: In this randomized, blinded study, the antihyperalgesic and antiedema effects of 3 dosages of BC were compared to a vehicle control. Inflammation was induced in rats by injecting complete Freund's adjuvant (CFA) into one hind paw. A single oral dose of the BC extract was administered daily for 7 days, beginning one day before CFA. Hyperalgesia was assessed using a paw withdrawal latency (PWL) test pre-CFA and 2 hours, 5 hours, 1 day, and 5 days post-CFA. Edema was determined by measuring paw thickness at the same time points. Spinal Fos protein expression was analyzed 2 hours post-CFA. Adverse effects of the extract were monitored by observing the animals closely for unusual behavioral changes.
Results: Compared to control, a dosage of 0.45 g/kg BC significantly lengthened PWL and reduced paw edema on day 5 post-CFA. At 0.90 g/kg, BC significantly lengthened PWL at 5 hours, 1 day, and 5 days, and reduced paw edema at 2 hours, 5 hours, 1 day, and 5 days. This dosage also significantly suppressed spinal Fos expression in the medial half of laminae I-II. At 1.80 g/kg, BC significantly lengthened PWL and reduced paw edema at all time points. No noticeable adverse effects were observed in animals given the lower dosages of BC, but adverse effects in some animals were observed at 1.80 g/kg per day. In the acute toxicity study, the maximal single dose of 2.50 g/kg produced no adverse effects in the treated rats during the 14 days of observation.
Conclusions: The data suggest that BC produces significant antihyperalgesia and anti-inflammation effects and that the antihyperalgesia may be mediated by suppressed inflammation-induced Fos expression in the spinal dorsal horn neurons.