Modulation of cholinergic, monoaminergic, and purinergic enzymes of the brain functions by bitter (Vernonia amygdalina) and water bitter (Struchium sparganophora) leaves extracts: comparison of phenolic constituents versus nootropic potentials

Abstract

This study investigated the possible neuroprotective properties of two commonly consumed tropical vegetables. The modulatory effects of Vernonia amygdalina (VA) and Struchium sparganophora (SS) on the activities of Na+/K+ ATPase, ecto-5′-nucleotidase, monoamine oxidase (MAO), acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and FeSO4-induced oxidative stress in rat brain homogenate were assessed. The result revealed that both vegetables inhibited AChE, BChE, MAO, and ecto-5’nucleotidase activities, but stimulated Na+/K+ ATPase activity in a concentration-dependent manner. The SS had a significantly higher (P ˂ 0.05) inhibitory effect on AChE (IC50 = 4.83 μg/mL), BChE (IC50 = 5.61 μg/mL), MAO (IC50 = 26.11 μg/mL), ecto-5′ nucleotidase (IC50 = 23.04 μg/mL) than VA [AChE (IC50 = 7.53 μg/mL), BChE (IC50 = 7.32 μg/mL), MAO (IC50 = 26.11 μg/mL), and ecto-5′ nucleotidase (IC50 = 42.35 μg/mL)]. Furthermore, SS (IC50 = 28.30 μg/mL) had a significantly higher (P < 0.05) stimulatory effect on Na+/K+ ATPase activity than VA (IC50 = 34.87 μg/mL). Both extracts exhibited a strong antioxidant properties as typified by their radicals (OH and DPPH) scavenging and Fe2+ chelating abilities, as well as inhibition of Fe2+-induced lipid peroxidation in rat brain homogenate. The HPLC fingerprint of VA and SS extracts revealed the presence of catechin, chlorogenic acid, caffeic acid, p-coumaric acid, rutin, orientin, quercitrin quercetin, and luteolin. The stimulation of Na+/K+ ATPase activity, inhibition of 5′-nucleotidase, AChE, BChE, and MAO activities as well as Fe2+-induced oxidative stress could be a possible mechanism through which VA and SS exerts neuroprotective properties.