HUMAN GROUP-II PHOSPHOLIPASE A(2) IN NORMAL AND DISEASED INTERVERTEBRAL DISCS

We measured calcium-dependent phospholipase A(2) (PLA(2)) activity and immunoreactive group II PLA(2) levels of 54 normal discs obtained fro m cadavers and 73 disc samples surgically obtained from patients with spinal disorders, including intervertebral disc herniations, spondylos is, and spondylolisthesis. Both cadaveric and surgical disc specimens contained about two-fold greater PLA(2) activity than the ileal mucosa , one of the richest sources of group II PLA(2). Discs of middle-aged cases had significantly higher activity than those of younger and elde r cases. In cadaveric normal discs, calcium-dependent PLA(2) activity was significantly higher in females than in males. Annulus fibrosus an d nucleus pulposus contained the same PLA(2) levels. In diseased discs , herniated fragments that had extruded or protruded out of the discs possessed lower activity than other parts of discs in the intervertebr al space. Immunoreactive group II PLA(2) levels of intervertebral disc s closely correlated with PLA(2) enzymatic activity. We purified a PLA (2) from human intervertebral disc to homogeneity to further identify the isozymic nature of discal PLA(2). Its NH2-terminal amino acid sequ ence and molecular weight were identical to those of human group II PL A(2). Immunohistochemical analysis using a monoclonal anti-group II PL A(2) antibody showed that in both annulus fibrosus and nucleus pulposu s chondrocytes contained intense group II PLA(2) immunoreactivity in t heir cytoplasm, and that the matrix contained no substantial immunorea ctivity. These results suggest that group II PLA(2) in chondrocytes ha s important physiological roles in discal ordinary metabolism, maintai ning discal homeostasis.