CHYMOPAPAIN-INDUCED REDUCTION OF PROINFLAMMATORY PHOSPHOLIPASE A(2) ACTIVITY AND AMELIORATION OF NEUROPATHIC BEHAVIORAL-CHANGES IN AN IN-VIVO MODEL OF ACUTE SCIATICA

The mechanism of action underlying chymopapain (Chymodiactin) chemonuc leolysis remains obscure. Radiographic studies suggest that chymopapai n does not alter disc fragment size acutely; nonetheless, patients oft en report symptom resolution within a few days, even hours, of treatme nt. The authors postulate that, in addition to its chemonucleolytic ac tion, chymopapain may possess antiinflammatory properties. To test thi s hypothesis, the authors assessed the ability of chymopapain to modul ate the activity of the proinflammatory enzyme phospholipase A(2) (PLA (2)) and to ameliorate behavioral changes associated with inflammatory neuropathy in an in vivo model of sciatica. Thirty-nine male Fischer rats were randomly assigned to one of three treatment groups: 1) salin e, 2) betamethasone, or 3) chymopapain. All of the rats underwent unil ateral sciatic nerve ligation with loose chromic gut suture to induce inflammatory mononeuropathy. The animals were tested for thermal and m echanical hyperalgesia on Days 0 (preoperation), 7 (pretreatment), and 14 (prior to death). Three animals were killed on Day 0 to determine the baseline PLA(2) activity within unmanipulated rat sciatic nerves. On Day 7, three animals from each group were killed to assess PLA(2) a ctivity prior to treatment. The remainder were given a single infusion of saline, betamethasone (0.3 mg/kg), or chymopapain (100 pKat U) aro und the inflamed nerve. On Day 14, the remaining animals were killed a nd their sciatic nerves were removed. The tissue was homogenized and t he PLA(2) activity was determined using [C-14]arachidonate-labeled Esc herichia coli phospholipid membrane as a substrate. Lipids were extrac ted and separated by thin-layer chromatography. All animals developed behavioral changes consistent with inflammatory mononeuropathy 24 to 7 2 hours postoperatively; these included gait disturbance, flexion defo rmity, and hyperalgesia of the involved hindlimb. The degree of mechan ical and thermal hyperalgesia was comparable between groups at Day 7. By Day 14, the thermal hyperalgesia had resolved; the mechanical hyper algesia was less evident in the betamethasone- and chymopapain-treated groups than in the saline-treated controls (p = 0.003; saline- vs. ch ymopapain-treated groups p = 0.004; saline- vs. betamethasone-treated groups p = 0.008). The mean PLA(2) activity at baseline (Day 0) was 11 .6 +/- 4.9 nmol phospholipid hydrolyzed per minute per milligram of pr otein. The PLA(2) activity at Day 7 was 74.4 +/- 18.2 (ligated side) a nd 21.2 +/- 11.7 (nonligated side). At Day 14, PLA(2) activity was red uced in the chymopapain- (47.8 +/- 12.3) and betamethasone- (39.7 +/- 9.5) treated groups compared with the saline control group (62.3 +/- 1 1.2), (saline- vs. chymopapain-treated groups p < 0.05; saline- vs. be tamethasone-treated groups p < 0.01). The PLA(2) activity in nonligate d specimens was 18.6 +/- 10.1. These data indicate that chymopapain ex hibits antiinflammatory properties in vivo, reducing PLA(2) activity a nd ameliorating mechanical hyperalgesia in this model of inflammatory sciatic neuropathy.