Anti-oxidant and Monoamine Oxidase Inhibition Studies on the Surface Exudates of Gardenia Ternifolia

Abstract

Numerous scientific studies point to oxidative stress (OS) as an important etiological factor in common diseases such as artherosclerosis, rheumatoid arthritis, tumors, cancer, diabetes, hypertension, cardiovascular and neurological diseases. Enzymes in the brain such as Monoamine Oxidases A and B work synergistically with Reactive Oxygen Species in the oxidative deamination of neurotransmitters enhancing the occurrences of neurological disorders such as depression, Alzheimer and parkinsonʼs diseases. Synthetic Monoamine Oxidase Inhibitors (MAOIS) have been developed to prevent this from happening towards improving and maintaining brain cell effective communication but the problem has persisted.The usage of these synthetic MAOIs has been reported to have many side effects associated with them just like the synthetic anti-oxidants. Butylated hydroxyanisole (BHA), Butylated hydroxytoluene (BHT) and tert-Butylhydroquinone (TBHQ). These include: blood pressure changes, headache, drowsiness and insomnia among others. Scientific evidences point to natural anti-oxidant molecules in plants as effective tools for the control of oxidative stress, and flavonoids are one of the major groups of anti-oxidants in plants most of which occur in their surface exudates. Gardenia ternifolia leaves are used to manage mental illness connected with neurotransmission in some countries like Uganda, Congo Brazaville among others. This study therefore, sought to investigate the anti-oxidant and MAO-Inhibition activities of the compounds found on the surface exudates of Gardenia ternifolia so as to improve the knowledge base and also in finding dietary supplements for MAO inhibition that could improve neurological conditions. Surface exudates of Gardenia ternifolia fresh leaves from Kagundo, Machakos County were extracted through consecutive dipping in fresh amounts of acetone for 15 seconds to get the crude extract. Chromatographic separation of the crude extract gave a total of six compounds which were successfully characterized using spectroscopic techniques and identified as 5,4ʼ-dihydroxy-7-methoxyflavanone (164), 3,5,4ʼ-trihydroxy-7-methoxyflavone (165), 5,7-dihydroxy-3,4ʼ-dimethoxyflavone (166), 3,3ʼ,5-trihydroxy-4ʼ,7-dimethoxyflavone (168), β-sitosterol(169) and stigmasterol (170). Compound 166 was transformed to 167 through acetylation. All the seven compounds were tested for their anti-oxidant and MAO Inhibition activity. The activity of the flavonoids showed that flavonols had better anti-oxidant activity as compared to 3-methoxyflavones isolated from the surface exudates of Gardenia ternifolia. The most active compound was 3, 3ʼ, 5-trihydroxy-4ʼ, 7-dimethoxyflavone (168) with IC50 of 40.3μΜ. The MAO-A and B inhibition activities revealed that 3, 4ʼ-methoxyflavones had better activity as compared to hydroxylated flavonoids in these positions. Compound 166 was the most active and more selective to MAO-A (IC50 = 0.033 μΜ), showing binding affinity of (Ki) 0.0379 μΜ compared to MAO-B (IC50 = 4.133μM). It also showed competitive reversible type of inhibition for the enzymatic active site. Acetylating the hydroxyl groups at C-5 and C-7 of compound 166 to 167 led to a decrease in MAO-A and B activities exhibiting IC50 =10.40 and 42.00 μM, respectively.The anti-oxidant and selective MAO-A inhibitory properties observed for the flavonoids isolated from the surface exudates of Gardenia ternifolia suggest their possibility in generating selective pharmacological influence that might be useful for the prevention of numerous free radical based diseases as well as in the management of depression and other related neurological disorders.