The monoterpene indole alkaloids (MIAs) are a group of secondary metabolites extensively investigated because of their therapeutic importance. Species of the Palicoureeae (Psychotrieae s. lat) tribe (Rubiaceae) are known to biosynthesize this class of compounds. Some of the genera belonging to the Palicoureeae tribe, as Palicourea, Psychotria and Rudgea, are chemo- and taxonomically very close. Considering the presence of psychoactive MIAs with β-carboline (βCs) nucleus in Psychotria species and its chemical closeness to Palicourea and Rudgea, in this study the alkaloid fractions (AFs) obtained from species of these three genera were evaluated for their inhibitory potential on monoamine oxidase A (MAO-A) and B (MAO-B), acetyl- (AChE) and butyrylcholinesterase (BChE). It was observed that none of the AFs was able to inhibit AChE. However, BChE and MAO-A activities were impaired by the Psychotria and Palicourea AFs, with lower IC50 of Psy. nemorosa. Rudgea AFs demonstrated a poor inhibitory profile on all targets. Taking into account that Psy. nemorosa displayed the best pharmacological results, it was chosen for further experiments. To optimize Psy. nemorosa alkaloids extraction, a pool of samples was submitted to ultrasound assisted extraction. A Fractional Factorial Design approach was used and taking as response the Euclidean distance measurements between the UPLC-DAD fingerprints and the blank injection, highly diverse samples were evidenced. Coupled with the calculation and plotting of effects per time point, it was possible to indicate thermolabile peaks. After screening, time and temperature were selected for optimization using a Central Composite Design (CCD). Finally, plant:solvent ratio was set at 1:50 (m/v), number of extractions at one, particle size at ≤ 180 µm, extraction time at 65 min and temperature at 45 °C, thus avoiding degradation. For the fractionation step, a solid phase extraction method was optimized by a Box-Behnken Design (BBD) approach. Sample concentration was consequently set at 150 mg/mL, % acetonitrile in dichloromethane at 40% as eluting solvent, and eluting volume at 30 mL. Based on the optimized method, the 43 collected samples were extracted and the AFs were analyzed by UPLC-DAD and assayed for their BChE and MAO-A inhibitory potency. In order to correlate chromatographic fingerprints and pharmacological activities, Orthogonal Projections to Latent Structure (O-PLS) modelling was employed and the regression coefficients of the model were analyzed and compared to the original fingerprints. Four peaks were indicated as multifunctional compounds, with the capacity to impair both BChE and MAO-A activities. In order to confirm these results, a semi-prepHPLC technique was used and a fraction containing the four peaks purified and evaluated in vitro. The fraction exhibited an IC50 of 2.12 µg mL-1 for BChE and 1.07 µg mL-1 for MAO-A. Summarizing, this study exploits the multifunctional potential of indole alkaloids obtained from the tribe Palicoureeae using different approaches. Strategies using the entire fingerprint to achieve the main goals were developed, based on chemometric approaches, reinforcing the importance of using multivariate data analysis in plant studies.
|Place of Publication||Brussels|
|Publication status||Published - 2016|