Analgesic effects of intra-articular botulinum toxin Type B in a murine model of chronic degenerative knee arthritis pain

Abstract

Objective: To evaluate the analgesic effectiveness of intra-articular botulinum toxin Type B (BoNT/B) in a murine model of chronic degenerative arthritis pain.

Methods and materials: Chronic arthritis was produced in adult C57Bl6 mice by intra-articular injection of Type IV collagenase into the left knee. Following induction of arthritis, the treatment group received intra-articular BoNT/B. Arthritic control groups were treated with intra-articular normal saline or sham injections. Pain behavior testing was performed prior to arthritis, after induction of arthritis, and following treatments. Pain behavior measures included analysis of gait impairment (spontaneous pain behavior) and joint tenderness evaluation (evoked pain response). Strength was measured as ability to grasp and cling.

Results: Visual gait analysis showed significant impairment of gait in arthritic mice that improved 43% after intra-articular BoNT/B, demonstrating a substantial articular analgesic effect. Joint tenderness, measured with evoked pain response scores, increased with arthritis induction and decreased 49.5% after intra-articular BoNT/B treatment. No improvement in visual gait scores or decrease in evoked pain response scores were found in the control groups receiving intra-articular normal saline or sham injections. Intra-articular BoNT/B was safe, and no systemic effects or limb weakness was noted.

Conclusions: This study is the first report of intra-articular BoNT/B for analgesia in a murine model of arthritis pain. The results of this study validate prior work using intra-articular neurotoxins in murine models. Our findings show chronic degenerative arthritis pain can be quantitated in a murine model by measuring gait impairment using visual gait analysis scores (spontaneous pain behavior) and joint tenderness scores (evoked pain responses). Reduction of joint pain seen in this study is consistent with our hypothesis of inhibition of release of pain mediators by intra-articular BoNT/B, supporting further investigation of this novel approach to treatment of arthritis pain with intra-articular neurotoxins.

Keywords: intra-articular BoNT/B; osteoarthritis.

Figures 1

A) Evoked pain response: Measurement of joint tenderness (left knee) and B) Spontaneous pain behavior: Measurement of gait changes. Notes: Seventeen mice with collagenase-induced arthritis of the left knee were treated at four weeks with intra-articular botulinum neurotoxin Type B (Myobloc^®) 0.02 IU in 5 μL of normal saline in the arthritic left knee. Animals were examined three days following intra-articular botulinum neurotoxin Type B to allow time for botulinum effects. Significant improvements in evoked pain response and spontaneous pain behavior (visual gait analysis) were noted following intra-articular botulinum neurotoxin Type B (P = 0.0134 and P = 0.0419, respectively). Gait improved by 43%, and evoked pain response was decreased by 49.5% following intra-articular botulinum neurotoxin Type B treatment. Treatment control groups included seven arthritic mice receiving either 5 or 10 μL intra-articular normal saline in the arthritic left knee at four weeks following intra-articular collagenase. Animals were examined three days following normal saline injections and compared with untreated arthritic animals (n = 40). No significant change in evoked pain response or spontaneous pain behavior (visual gait analysis) was noted following intra-articular normal saline (P = 0.9043 and P = 0.2250, respectively). Abbreviations: naïve, 40 animals prior to induction of arthritis in the left knee; Arthritic, 40 animals four weeks post intra-articular collagenase into the arthritic left knee; Arth/BoNT/B, 17 animals four weeks post intra-articular collagenase into the left knee (arthritic), three days post intra-articular botulinum neurotoxin Type B into the arthritic left knee; Arth/saline, seven animals four weeks post intra-articular collagenase into the left knee (arthritic), three days post intra-articular saline into the arthritic left knee.

Figure 2

Safety assessment: Limb strength. Notes: The 17 animals receiving intra-articular botulinum neurotoxin Type B were assessed for changes in strength three days following intra-articular botulinum neurotoxin Type B. No significant change in grasp or cling scores were noted following intra-articular botulinum neurotoxin Type B compared with untreated arthritic animals (P = 0.0704 and P = 0.2752, respectively). The seven animals receiving intra-articular normal saline injections had no significant change in grasp or cling scores (P = 0.3964, P = 0.7457, respectively). Abbreviations: arthritic, 40 animals four weeks post intra-articular collagenase into the arthritic left knee; Arth/BoNT B, 17 animals four weeks post intra-articular collagenase into the left knee (arthritic), three days post intra-articular botulinum neurotoxin Type B into the arthritic left knee; Arth/saline, seven animals four weeks post intra-articular collagenase into the left knee (arthritic), three days post intra-articular saline into the arthritic left knee.

Figure 3

Hematoxylin and eosin stained normal right knee. Note: Normal-appearing articular cartilage (arrowhead), meniscus (arrow), and synovium (asterisk).

Figure 4

Arthritic left knee stained with hematoxylin and eosin. Note: Irregularities and thinning of articular cartilage (arrowheads) and early osteophyte formation (arrow) consistent with degenerative arthritis.