High levels of inflammatory phospholipase A2 activity in lumbar disc herniations

Inflammation of neural elements is frequently mentioned clinically in association with lumbar radiculopathy. Mechanical embarrassment of neural elements by definable structural abnormalities is inadequate as a sole explanation of nerve injury in this condition. The purpose of this study was to demonstrate whether an enzymatic marker for inflammation (phospholipase A2) could be identified in human disc samples removed at surgery for radiculopathy due to lumbar disc disease. Samples were assayed for phospholipase A2 activity. The level of activity in the disc samples was compared with values obtained from other human tissues using the same assay. Specific activity (percent hydrolysis radiolabelled substrate) ranged from 238 to 1,014.5 nmol/min/mg. Mean activity for the human disc material was 568.7 nmol/min/mg, compared with 0.006 nmol/min/mg for human PMN, and 12.1 nmol/min/mg for inflammatory human synovial effusion. The pH and cation-related activity were identical to those demonstrated for phospholipase A2 inflammatory conditions. Human lumbar disc phospholipase A2 activity is from 20- to 100,000-fold more active than any other phospholipase A2 that has been described. As the enzyme responsible for the liberation of arachidonic acid from cell membranes, phospholipase A2 is the rate-limiting step in the production of prostaglandins and leukotrienes. These data establish biochemical evidence of inflammation at the site of lumbar disc herniations.