Partial characterization of apoptotic factor in Alzheimer plasma

We have previously demonstrated that a plasma natriuretic factor is present in Alzheimer's disease (AD), but not in multi-infarct dementia (MID) or no rmal controls (C). We postulated that the natriuretic factor might induce t he increased cytosolic calcium reported in AD by inhibiting the sodium-calc ium antiporter, thereby activating the apoptotic pathway. To test for a fac tor in AD plasma that induces apoptosis, we exposed nonconfluent cultured L LC-PK1 cells to plasma from AD, MID, and C for 2 h and performed a terminal transferase-dUTP-nick-end labeling (TUNEL) assay. The plasma from AD incre ased apoptosis nearly fourfold compared with MID and C. The effect was dose dependent and the peak effect was attained after a 2-h exposure. Additiona lly, apoptotic morphology was detected by electron microscopy, and internuc leosomal DNA cleavage was found. We inhibited apoptosis by removing calcium from the medium, inhibiting protein synthesis with cycloheximide, alternat ely boiling or freezing and thawing the plasma, and digesting a partially p urified fraction with trypsin. Heating AD plasma to 56 degrees C did not de activate the apoptotic factor. These results demonstrate the presence of an apoptotic factor in the plasma of patients with AD.