PURIFICATION AND IDENTIFICATION OF BRAIN-DERIVED NEUROTROPHIC FACTOR FROM HUMAN SERUM

Brain-derived neurotrophic factor (BDNF), a 27-kDa noncovalently linke d homodimer with subunits of approximate to 13.5 kDa as viewed by SDS- PAGE, is thought to be primarily produced in the central nervous syste m. We report here the isolation of BDNF from pooled normal human sera, using a two-step purification process followed by SDS-PAGE, transfer to a polyvinylidene difluoride membrane, and subsequent identification of the protein by sequence analysis of the appropriate band(s) from t he membrane. The level of BDNF in pooled human sera was estimated to b e approximately 15 ng/ml as determined by an enzyme-linked immunosorba nt assay. The average for six individuals was 18.9 +/- 5.7 ng/ml. Ther e is an approximately 200-fold increase in the levels of BDNF in serum relative to plasma. Results from experiments using differential centr ifugation suggest that the source of this increase is due to release f rom platelets. The presence of high levels of BDNF in serum suggests a role for this neurotrophin either in nerve repair at sites of injured tissue or in nonneuronal functions. (C) 1995 Academic Press, Inc.