Accumulation of non-erythroid alpha II-spectrin and calpain-cleaved alpha II-spectrin breakdown products in cerebrospinal fluid after traumatic braininjury in rats

Although a number of increased CSF proteins have been correlated with brain damage and outcome after traumatic brain injury (TBI), a major limitation of currently tested biomarkers is a lack of specificity for defining neurop athological cascades. Identification of surrogate biomarkers that are eleva ted in CSF in response to brain injury and that offer insight into one or m ore pathological neurochemical events will provide critical information for appropriate administration of therapeutic compounds for treatment of TBI p atients. Nonerythroid all-spectrin is a cytoskeletal protein that is a subs trate of both calpain and caspase-3 cysteine proteases. As we have previous ly demonstrated, cleavage of all-spectrin by calpain and caspase-3 results in accumulation of protease-specific spectrin breakdown products (SBDPs) th at can be used to monitor the magnitude and temporal duration of protease a ctivation. However, accumulation of all-spectrin and alpha II-SBDPs in CSF after TBI has never been examined. Following a moderate level (2.0 mm) of c ontrolled cortical impact TBI in rodents, native alpha II-spectrin protein was decreased in brain tissue and increased in CSF from 24 h to 72 h after injury. In addition, calpain-specific SBDPs were observed to increase in bo th brain and CSF after injury. Increases in the calpain-specific 145 kDa SB DP in CSF were 244%, 530% and 665% of sham-injured control animals at 24 h, 48 h and 72 h after TBI, respectively. The caspase-3-specific SBDP was obs erved to increase in CSF in some animals but to a lesser degree. Importantl y, levels of these proteins were undetectable in CSF of uninjured control r ats. These results indicate that detection of alpha II-spectrin and alpha I I-SBDPs is a powerful discriminator of outcome and protease activation afte r TBI. In accord with our previous studies, results also indicate that calp ain may be a more important effector of cell death after moderate TBI than caspase-3.