Uleine Disrupts Key Enzymatic and Non-Enzymatic Biomarkers that Leads to Alzheimer's Disease.

Alzheimer´s disease, a progressive and degenerative disorder of the brain, is the most common cause of dementia among the elderly. To face its multifactorial nature, the use of single compounds that can simultaneously modulate different targets involved in the neurodegenerative cascade has emerged as an interesting therapeutic approach. This work investigated the ability of uleine, the major indole alkaloid purified from stem barks of the Brazilian medicinal plant Himatanthus lancifolius, to interact with crucial Alzheimer´s disease disruptive targets associated with two of its major neurodegenerative pathways: acetylcholinesterase and butyrylcholinesterase (cholinergic pathway) and β-secretase and β-amyloid peptide (amyloidogenic pathway). Uleine's capacity to inhibit human acetylcholinesterase and butyrylcholinesterase enzymes was determined measuring the difference between reaction rates with and without uleine monitored at 412 nm using 5,5'- dithiobis-(2- nitrobenzoic acid) as colorimetric agent. FRET based assay was used to evaluate β-secretase inhibition using DABCYL- Ser-Glu-Val-Asn-Leu-Asp-Ala-Glu-Phe-EDANS as substrate and β-amyloid peptide spontaneous aggregation assay was performed using the thioflavin T spectroscopy assay. Cell viability and toxicity experiments with PC12 and SH-SY5Y cell lines were performed using the MTT colorimetric assay. Uleine demonstrated strong inhibitory activities for both cholinesterases (IC50 279.0±4.5 and 24.0±1.5 μM, respectively) and β-secretase (IC50 180±22 nM). Above all, uleine significantly inhibited the self-aggregation of amyloid- β peptide and was not toxic for PC12 or SH-SY5Y neuronal cells. These data show for the first time that the natural compound uleine has a novel, multieffective ability to decelerate or even inhibit the development of Alzheimer´s disease.