Prospecção das propriedades farmacobotânicas do óleo essencial in natura e nanoencapsulado de Siparuna guianensis Aubl. em modelo experimental para doença de Alzheimer

Abstract

The increase in life expectancy of the population of countries developed and in development, has been the main cause of the increase in the number of diagnoses of Alzheimer's disease (AD) whose evolution causes the progressive and irreversible loss of neurons that form the hippocampus. The main treatment of AD involves the use of inhibitors of the enzyme acetylcholinesterase (AChE) to maintain optimal concentrations of the neurotransmitter acetylcholine in the synaptic cleft and thus reestablish synapses between neurons. The plant popularly known as "negramina", belonging to the Siparunaceae family, produces an essential oil that has several biological activities, including the ability to inhibit AChE. One way to increase the effectiveness of AChE inhibitors and carry out their transport to target cells overcoming brain barriers is the use of nanotechnological techniques. Finally, the in vivo model using the nematode Caenorhabditis elegans is an effective tool to evaluate mechanisms of action and perform the screening of neuroprotective substances for the treatment of neurodegenerative diseases. Therefore, the objective of this work was to carry out an interaction study between the essential oil of the plant Siparuna guianensis Aubl. (OESG) and AChE as well as producing chitosan-coated PLGA nanocapsules (NCSG) in order to potentiate their inhibitory action in addition to evaluating their protective activity in Alzheimer models using the nematode C. elegans. The essential oil was extracted from fresh leaves collected in the state of Roraima, in the extreme north of the Amazon. The chemical composition of the essential oil was characterized by means of gas chromatography coupled to mass spectrometry (GC-MS) and flame ionization detector (CG-FID). The interaction between the essential oil and the enzyme was investigated using spectroscopic techniques such as 1H NMR and fluorescence suppression titration at 25, 30 and 35 °C, in addition to colorimetric methods and molecular docking. The nanocapsules were produced by means of nanoprecipitation and characterized using a ZetaSizer particle analyzer. The stability of the nanosystem was evaluated during 30 days of storage at 25ºC. The sesquiterpenoid shyobunone and its derivatives were identified as the major components, corresponding to more than 40% of the essential oil concentration. Regarding fluorescence suppression, the values obtained for the Stern-Volmer constants for temperatures of 25, 30 and 35 °C were 7.06 106 M-1, 1.1 106 M-1 and 0.06 106 M-1, respectively. The reaction was characterized as static suppression. The spectra obtained with the 1H NMR titration suggest a shielding of shyobunone hydrogens during contact with AChE, indicating a possible interaction between the enzyme and shyobunone. Spectrophotometric results revealed that shyobunone and its derivatives bind very strongly to AChE in a competitive inhibitory mechanism and interaction studies support the findings of enzyme inhibition. The in silico molecular docking experiment showed that most molecules bind slightly stronger at the A site, with persistent hydrophobic interactions with Trp108 and Tyr355. The PLGA nanocapsules containing the OESG exhibited a particle diameter of 255 ± 1.44 nm, with a polydispersity index of 0.192 ± 0.35 and Zeta potential -10.5 ± 0.44 mV, being stable during 30 days of analysis. PLGA nanocapsules containing OESG coated with chitosan exhibited a particle diameter of 112.8 ± 0.51 nm, with a polydispersity index of 0.342 ± 0.036 and a Zeta potential of 26.5 ± 0.95 mV. The results of this research suggests that OESG showed antioxidant and anticholinesterase activity in vitro and in vivo, with NCSG being more effective, but no effect against proteotoxic stress was observed. Certainly, the effective nanoencapsulation of OESG suggests that natural products such as essential oils can have their therapeutic effect potentiated, providing new insights to develop treatment strategies for neurodegenerative diseases such as AD.