A controlled biochemical and immunohistochemical study of human synovial-type (group II) phospholipase A2 and inflammatory cells in macroscopically normal, degenerated, and herniated human lumbar disc tissues.

STUDY DESIGN

Group II phospholipase A2 enzyme activity was studied biochemically and immunohistochemically in tissue samples from disc prolapses, degenerated discs, and macroscopically normal discs. In parallel, phospholipase A2 and inflammatory cells were studied by indirect immunocytochemistry.

OBJECTIVES

To compare phospholipase A2 activity in normal discs and abnormal discs by an identical assay for phospholipases A2, and to compare the occurrence of inflammatory cells with phospholipase A2 activity and immunoreactivity.

SUMMARY OF BACKGROUND DATA

It has been suggested that a high phospholipase A2 enzyme activity in herniated disc tissue could be significant in abnormal states such as sciatica and discogenic pain. No comparison between healthy disc tissue and samples of abnormal discs (degenerated or herniated) has been carried out. In particular, an identical assay for phospholipase A2 for such tissue samples, supported by immunohistochemical staining data, has never been applied in parallel to normal and abnormal disc tissue, and neither have such results been compared with the demonstration of inflammatory cells.

METHODS

Group II phospholipase A2 enzyme activity was determined, in parallel, using an identical assay for tissue samples from 11 macroscopically normal discs, 33 disc herniations, and six discs showing degeneration by discography. For determination of phospholipase A2 enzyme activity, a radioassay using 1-palmitoyl-2-(1-14C)linoleoyl-L-3-phosphatidylethanolamine as the phospholipid substrate was used. Total tissue DNA as an estimate of total tissue cell number was measured in parallel with phospholipase A2 activity. All tissue samples also were studied by indirect immunocytochemistry, locating phospholipase A2 and T and B lymphocytes.

RESULTS

Neither degenerated nor herniated disc tissue samples demonstrated a higher phospholipase A2 activity than control disc tissue samples. Average phospholipase A2 activity was actually higher in the control samples than in herniated disc samples (Mann-Whitney test, P < 0.001), possibly a result of a higher total DNA (P < 0.005). The observed level of phospholipase A2 activity was lower than that of inflammatory human synovial fluid. Neither was there marked immunoreactivity for phospholipase A2, which was observed in chondrocytes in areas of cartilage and occasional disc cells, supporting the biochemical results. Lymphocytes were more numerous only in herniated disc samples (15%), and their presence showed little overlap with phospholipase A2 immunoreactivity.

CONCLUSIONS

Synovial-type (Group II) phospholipase A2 enzyme activity is not particularly high in disc tissue and does not appear to be higher in herniated or degenerated discs than control disc tissue. Immunoreactivity to phospholipase A2 is seen only occasionally and is strong only when cartilage tissue is present. Neither are inflammatory lymphocytes commonly observed.