Neurobiological evaluation of thirty-one medicinal plant extracts using microtiter enzyme assays

Abstract

Background: Inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) related to Alzheimer's disease as well as tyrosinase (TYR) relevant to Parkinson's disease is an important approach to find novel drug candidates for these diseases. Methods: The extracts from fourteen plant species in various polarities were subjected to high-throughput screening against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and tyrosinase (TYR), the key enzymes related to Alzheimer's and Parkinson's diseases. The extracts were subjected to the microtiter enzyme inhibition assays at 100 µg mL-1. Antioxidant effect of the extracts was tested for their scavenging activity against DPPH, DMPD, and NO radicals as well as their ferric- (FRAP) and phosphomolibdenum-reducing power (PRAP) and metalchelation capacity. Total phenol and flavonoid quantities in the extracts were determined spectrophotometrically. HPLC analysis was performed on Atriplex lasiantha, Conringia grandiflora, and Vaccaria hispanica. Results: The active extracts inhibiting AChE over 50% were Centaurium erythraea subsp. rhodense (51.33±3.35%) and Posidonia oceanica (61.88±2.23%), while BChE was inhibited most effectively by the root extract of P. oceanica (82.55±2.14%), followed by Origanum haussknechtii (66.88±0.17%), which also had the highest inhibition toward TYR (35.28±1.90%). The extracts from Zostera noltii, P. oceanica, and Ricotia carnosula possessed the best DPPH scavenging activity, whereas Z. noltii caused the highest NO scavenging activity (70.19±0.43%) and FRAP (1.326±0.065). Atriplex lasiantha and Ecballium elaterium had the strongest effect in PRAP and metal-chelation assays, respectively. Besides, A. lasiantha was found to be a rich source of rutin. Conclusion: Among the screened plants, Centaurium erythraea subsp. rhodense and Origanum haussknechtii, and the roots of Posidonia oceanica seems to deserve further investigation for their neuroprotective potential.