Salt Stress Enhanced Bioactivity of Quinoa Leaf Extracts: An In Vitro and In Silico Study of Acetylcholinesterase and Tyrosinase Inhibition for Sustainable Drug Development

Background: Quinoa is recognized for its nutritional and pharmacological properties. This study aims to investigate the impact of salt stress induced by varying concentrations of sodium chloride (NaCl) on the production of phenolic compounds and their biological activities in different quinoa accessions. Method: Leaves from three quinoa accessions (Q4, Q24, and Q45) cultivated under increasing NaCl treatments were subjected to chemical analysis using ethanol and water extract. The concentrations of various phenolic compounds, including polyphenols, tannins, anthocyanins, and flavonoids, were quantified. HPLC-DAD-ESI-MS/MS was employed to identify the major compounds in the water extract. Additionally, antioxidants (ABTS and FRAP), anti-tyrosinase, and anti-acetylcholinesterase effects were assessed using in vitro and in silico approaches. Results: NaCl treatment significantly increased the levels of phenolic compounds across all quinoa accessions. The Q45 accession exhibited the highest accumulation of these compounds, particularly in the aqueous extracts at the 200 mM NaCl concentration. Increases were observed in flavonoids (144%), anthocyanins (125%), tannins (89%), and total polyphenols (65%) relative to controls. HPLC-DAD-ESI-MS/MS analysis corroborated these findings, showing that the main compounds also increased with higher NaCl concentrations. Furthermore, the biological efficacy tests revealed that the IC₅₀ values for both tyrosinase and acetylcholinesterase activities decreased with greater salt stress, indicating enhanced enzyme inhibition. The antioxidant activity of these extracts also showed a significant increase as the salt stress levels rose. Conclusions: Salt stress not only promotes the production of bioactive phenolic compounds in quinoa leaves but also enhances their inhibitory effects on key enzymes associated with neurodegenerative and pigmentary disorders. These findings suggest that quinoa may serve as a valuable resource for therapeutic applications, particularly under increased salinity conditions.