EFFECT OF SORREL (Hibiscus sabdariffa), HIBISCUS FLOWER (Hibiscus rosa sinesis) AND SORGHUM STEM (Sorghum bicolor) EXTRACTS ON CHOLINERGIC, MONOAMINERGIC AND PURINERGIC ENZYMES RELEVANT TO NEURODEGENERATION

Abstract

This study sought to assess the antioxidant activities and effects of phenolic extracts from sorrel (Hibiscus sabdariffa), hibiscus flower (Hibiscus rosa sinenis) and sorghum stem (Sorghum bicolor) on some enzymes of the cholinergic (acetylcholinesterase (AChE) and butyrylchlinesterase (BChE)), monoaminergic (monoamine oxidase (MAO)) and purinergic (Na+/ K+-ATPase, Ecto-5'-nucleotidase and ATPDase) systems relevant to the management of neurodegenerative conditions. Phenolic-rich extracts were prepared using methanol: 1N HCL (1:1, v/v) mixture; and the ability of the extracts to inhibit Fe2+, Sodium nitropusside (SNP) and quinolinic acid-induced malondialdehyde (MDA) production in rat’s brain homogenates were assessed. Furthermore, the antioxidant activities of the extracts as typified by the Fe2+-chelation and radicals (DPPH* and OH*) scavenging abilities were investigated. The total phenolic and flavonoid contents were determined and identified by high performance liquid chromatography coupled with a diode array detector (HPLC-DAD). The results revealed that Sorghum had the highest Na+/K+-ATPase (IC50 = 19.49μg/ml) stimulatory activity as well as AChE (IC50 = 24.88μg/ml) and Ecto-5'-nucleotidase (IC50 = 375.49 μg/ml) inhibitory activities; while hibiscus had the highest BChE (IC50 = 40.38μg/ml) and ATPDase (IC50 = 82.46μg/ml) inhibitory activities. Also, sorghum had the highest OH* (IC50 = 54.27μg/ml) scavenging and Fe chelating (18.47μg/ml)] abilities. Sorrel had the strongest inhibition of MAO activity and pro-oxidants (Fe2+, SNP, quinolinic acid) induced MDA production in rat brain. HPLC analysis revealed the presence of quercetrin and caffeic acid as the most abundant flavonoid and phenolic acid. Consequently, the modulation of cholinergic, monoaminergic and purinergic enzymes and their antioxidant properties could be linked to their phenolic contents and could underline the possible mechanisms of their neuroprotective effect.