Partial characterization of apoptotic factor in Alzheimer plasma

• Published in: American journal of physiology. Renal physiology 1999-04, Vol.276 (4), p.F521
• Main Authors: Maesaka, John K, Palaia, Thomas, Chowdhury, Soheli A, Shimamura, Tetsuo, Fishbane, Steven, Reichman, William, Coyne, Andrew, O'Rear, Julian J, El-Sabban, Marwan E
• Format: Article
• Language: English
• ISSN: 1522-1466

We have previously demonstrated that a plasma natriuretic factor is present in Alzheimer's disease (AD), but not in multi-infarct dementia (MID) or normal controls (C). We postulated that the natriuretic factor might induce the increased cytosolic calcium reported in AD by inhibiting the sodium-calcium antiporter, thereby activating the apoptotic pathway. To test for a factor in AD plasma that induces apoptosis, we exposed nonconfluent cultured LLC-PK 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 increased apoptosis nearly fourfold compared with MID and C. The effect was dose dependent and the peak effect was attained after a 2-h exposure. Additionally, apoptotic morphology was detected by electron microscopy, and internucleosomal DNA cleavage was found. We inhibited apoptosis by removing calcium from the medium, inhibiting protein synthesis with cycloheximide, alternately boiling or freezing and thawing the plasma, and digesting a partially purified fraction with trypsin. Heating AD plasma to 56°C did not deactivate the apoptotic factor. These results demonstrate the presence of an apoptotic factor in the plasma of patients with AD.