Exogenous nitric oxide induces production of phenolic compounds, enzyme inhibitory properties and antioxidant capacity through activating the phenylpropanoid pathway in sage (Salvia officinalis) leaves

Phenolic substances are crucial for the diverse biological activities of Salvia L. species, highlighting their importance for potential therapeutic applications. In the current study, the effects of nitric oxide (0, 100, and 1000 µM NO; donor diethylenetriamine NONOate) on the levels of phenolic compounds, total polyphenols, antioxidant capacity, and enzyme inhibitory features of the methanolic leaf extracts of sage (S. officinalis L.) were determined. Also, the impact of NO on the transcript level of some essential genes associated with the phenylpropanoid pathway was assessed. Rosmarinic acid (RA) was identified as the predominant phenolic compound, with its concentration rising from 4639.7 µg/g in the control to 5693.4 µg/g at 100 µM NO. The highest values of total phenolic (TPC, 117.81 mg GAE/g) and flavonoid contents (TFC, 39.86 mg QE/g) were observed in S. officinalis plants treated with 100 µM NO. Higher levels of antiradical scavenging activity (ABTS and DPPH), metal reducing potential (CUPRAC and FRAP), metal chelating ability (MCA), and total antioxidant capacity (TAC) correlated with these enhancements. Enzyme inhibition assays showed that NO-elicited extracts exhibited stronger acetylcholinesterase (AChE), butyrylcholinesterase (BChE), tyrosinase, and α-glucosidase inhibition, suggesting multiple health-promoting properties. Gene expression analysis revealed upregulation of phenylalanine ammonia-lyase (PAL), tyrosine aminotransferase (TAT), and rosmarinic acid synthase (RAS) genes in NO-treated samples, aligning with the elevated RA content and biological activities. Molecular docking studies unveiled that RA has strong interactions with AChE, BChE, α-amylase, and α˗glucosidase inhibition. Pearson's correlation analysis underscored strong positive relationships among phenolic content, antioxidant capacity, enzyme inhibition, and gene expression. Collectively, these findings suggest that NO elicitation can significantly boost the bioactive and therapeutic potential of sage leaves.