Calpain inhibition by cerebrospinal fluid and effects of calpain on intrathecal nerve tissue

The effects of calpain on intrathecal nerve tissue in the rabbit were investigated. To evaluate the chemonucleolytic side effect of calpain on nerve tissue in the event of accidental intrathecal calpain injection. Calpain has a degradative effect on proteoglycans, and as previously shown, it is associated with chemonucleolytic action in the rabbit. However, its effect on nerve tissue in the event of accidental intrathecal injection is not clear. The inhibitory activity of cerebrospinal fluid against calpain was measured in human cerebrospinal fluid using mu-calpain, and in different cerebrospinal fluid fractions separated by molecular filtration. The presence of the endogenous calpain inhibitor, calpastatin, in human cerebrospinal fluid was examined by Western blotting with anticalpastatin antibody. After intrathecal application of calpain in rabbits, the spinal cord nerve tissue was examined by light microscopy. Cerebrospinal fluid inhibited the enzyme reaction of calpain at its normal concentration. Immunoblotting with anticalpastatin antibody did not yield positive staining. After the intrathecal application of calpain, there was no evidence of degeneration in the nerve tissue of the spinal cord. This study suggests that in the event of accidental intrathecal injection of calpain for chemonucleolysis, the enzyme activity of calpain will be neutralized by cerebrospinal fluid, and the calpain should not cause unwanted side effects in chemonucleolysis.