Anticholinergic and antioxidant activities of usnic acid-an activity-structure insight

Usnic acid, as active dibenzofuran derivative, isolated and characterized from some lichen species. The aim of manuscript was to evaluate antioxidant, anticholinergic and antidiabetic potentials of usnic acid as an important natural product. Antioxidant profile of usnic acid determined by eight distinguishes bioanalytical antioxidant methods including 1,1-diphenyl-2-picrylhydrazyl (DPPH·), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS^{• +}), superoxide anion radical (O₂ ^{• -}) and N,N-dimethyl-p-phenylenediamine (DMPD^{• +}) scavenging activities, cupric ion (Cu²⁺), ferric ion (Fe³⁺) and Fe³⁺-TPTZ reducing abilities and ferrous ion (Fe³⁺) chelating activity. Usnic acid was found as potent DPPH· (IC₅₀: 49.50 μg/mL), DMPD^{• +} (IC₅₀: 33.00 μg/mL), O₂ ^{• -} (IC₅₀: 18.68 μg/mL), and ABTS^{• +} (IC₅₀: 10.41 μg/mL) scavenging effects. Also, the inhibition effects of usnic acid were tested against some metabolic enzymes including acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) linked to neurodegenerative diseases. Both enzymes play important roles in cholinergic transmission by hydrolyzing the neurotransmitter acetylcholine in cholinergic synapses, central nervous system, neuromuscular junctions and autonomic ganglia. Their inhibitors were used for clinical treatment of some neurodegenerative conditions including myasthenia gravis, Alzheimer's disease, apathy, glaucoma, postural tachycardia syndrome and dementia. Furthermore, usnic acid showed the potent inhibition profiles against AChE (IC₅₀: 1.273 nM) and BChE (IC₅₀: 0.239 nM) enzymes. The results clearly showed that usnic acid is an important natural product with antioxidant and anticholinergic potentials.