Background: The deposition of intracellular and extracellular beta-amyloidpeptide (Abeta) in the brain is a pathologic feature of Alzheimer's disease (AD), a prevalent neurodegenerativedisorder. However, the exact role of the Abeta peptide in causing AD's symptoms is unclear. Material/Methods:CRL-2266 SH-SY5Y human neuroblastoma cells (ATCC, USA) and HTB-11 human neuroblastoma cells (ATCC, USA)were cultured. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to analyze theeffects of beta25-35, morphine, and SNAP treatments upon BACE-1 and BACE-2 mRNA expression semi-quantitativeRT-PCR. The production of NO in SH-SY5Y cells was detected using the Apollo 4000 Free Radical Analyzer(World Precision Instruments). Results: Untreated HTB-11 neuroblastoma cells constitutively express BACE-1and BACE-2 mRNA. Morphine down regulates the expression of BACE-1 and up regulates the expression ofBACE-2 in a naloxone antagonizable manner. When HTB-11 cells were treated with L-NAME, a cNOS inhibitor;the effects of morphine were blocked. SNAP (a NO donor) mimicked the effect of morphine. In SH-SY5Y cells,Abeta treated cells show a dose-dependent decrease in NO release, demonstrating that Ab is dose-dependentlyinhibiting the release of constitutive NO. Conclusions: Ab and morphine/NO each inhibit the productionof the other. This suggests that a deficiency of basal NO or endogenous morphine may trigger drasticallyreduced levels of basal NO. The outcome is chronic vasoconstriction and brain hypoperfusion and eventualneuronal death. This novel theorized mechanism for AD supports an increasingly-accepted vascular pathologicalhypothesis for the disease.

Keywords: Aspartic Acid Endopeptidases - genetics, Amyloid beta-Peptides - metabolism, Amyloid Precursor Protein Secretases, Alzheimer Disease - prevention & control, Endopeptidases - genetics, Gene Expression Regulation, Enzymologic - physiology, Morphine - pharmacology, Nitric Oxide - physiology, RNA, Messenger - genetics, Reverse Transcriptase Polymerase Chain Reaction