Browsing by Author "Munaweera, R.R.K.W."

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    Determination of Antioxidant and Antimicrobial Activities of Psidium guineense Sw. Leaf Extracts Fractioned Based on Polarity
    (19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Munaweera, R.R.K.W.; Senanayake, C.; Algama, H.; Seneviratne, K.; Jayathilaka, N.
    Psidium guineense Sw. is a guava species distributed in South America, some parts of Africa and South Asia including Sri Lanka. Our previous studies have shown that Psidium guineense Sw. leaves contain 195.25±9.56 mg g-1 phenolic substances and 70 % ethanolic extract of P. guineense Sw. Leaves (PGLE) improve the oxidative stability and microbial shelf life of vanilla cake. PGLE may contain highly polar as well as medium and low polar phenolic substances. Therefore, antioxidant activity and antimicrobial activity of the further fractionated portions by chloroform and hexane of PGLE on food spoilage bacteria were determined. For this purpose, PGLE was obtained by solvent extraction and solvents of PGLE and different fractions were evaporated and reconstituted in 10 % ethanol. The antioxidant activities of solvent fractions, BHT and PGLE measured using DPPH radical scavenging assay are given in Figure 1. Figure 1. DPPH radical scavenging activity The antimicrobial activities of PGLE, chloroform fraction of PGLE and hexane fraction of PGLE were determined using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay for four microbial strains, two gram negative; Escherichia coli and Salmonella typhimurium and two gram positive; Bacillus cereus and Staphylococcus aureus. Ethanol from the extracts was maintained at 1% in the antimicrobial assays. PGLE showed the higher antimicrobial activity towards gram positive bacteria with LD50 values of 190.4 ± 20.2 mg/L for Staphylococcus aureus and 305.4 ± 22.4 mg/L for Bacillus cereus than gram negative bacteria with LD50 of 444.9 ± 13.0 mg/L for Escherichia coli and 508.6 ± 64.7 mg/L for Salmonella typhi. Streptomycin and chloramphenicol were used as positive controls. No antimicrobial activity was observed for chloroform and hexane fractions of PGLE in the four bacterial strains tested. The results of the present study suggest that phenolic compounds with medium polarity may be mainly responsible for antioxidant activity while phenolic compounds with high polarity may be responsible for antimicrobial activity.
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    Molecular Docking Analysis to Elucidate the Potential Drug Action of Phytochemicals Present in Ashwagandharishta towards Memory Related Disorders
    (19th Conference on Postgraduate Research, International Postgraduate Research Conference 2018, Faculty of Graduate Studies,University of Kelaniya, Sri Lanka, 2018) Munaweera, R.R.K.W.; Pandithavidana, D.R.
    Ashwagandharishta is an Ayurveda medicine that is used to treat psychiatric conditions, dullness, memory related diseases, sluggishness, epilepsy, depression, anxiety, schizophrenia. The main plant ingredient used to prepare this is Withaniasomnifera. It contains various classes of secondary metabolites such as steroidal lactones, phytosterols, sitoindosides and alkaloids. Memory-related disorders are closely associated with the defects in cholinergic neurotransmission. Repairing mechanisms for theses defects provide promising treatment strategies for these kinds of disorders. The most abundant receptor found in cholinergic neurotransmission is nicotinic acetylcholine receptor. Alpha-7 nicotinic acetylcholine receptor is a sub type of nicotinic acetylcholine receptor and has been identified as one of the most useful drug target for the treatment of nervous system related disorders. Potential agonists of alpha-7 nicotinic acetylcholine receptor have shown to be enhancers of cognitive performance when memory related disorders are treated. Molecular docking analyses have been carried out to identify any possible secondary metabolites present in Ashwagandharishta that could act as agonists of alpha-7 nicotinic acetylcholine receptor using AutoDock4 software package. Four possible phytochemicals have been selected based on drug likeness, blood brain barrier penetrability and agonistic binding ability with the receptor. Their docked conformations, binding at correct binding site, binding energies and dissociation constants (kI) have been further investigated computationally Based on the molecular docking studies it was revealed that anaferine and anahygrine possessed lower binding energies with compared to the binding energy of nicotine while cuscohygrine showed relatively higher energy in binding. When kI (dissociation constant) values were compared, anaferine and anahygrine possessed relatively higher values than that of nicotine. According to computational studies, cuscohygrine and palletierine showed some tendency to bind nonspecifically at other sites of the receptor. However, nonspecific bindings for anaferine and anahygrine were not energetically favorable. According this computational investigation, it has been found that two phytochemicals (anaferine and anahygrine) show promising agonistic activity towards the receptor. Thus anaferine and anahygrine have high possibility to serve as alpha-7nAChR agonists which show potential drug action towards memory related disorders.